research on atomic bombs

The Atomic Bomb and the End of World War II

A Collection of Primary Sources

Updated National Security Archive Posting Marks 75th Anniversary of the Atomic Bombings of Japan and the End of World War II

Extensive Compilation of Primary Source Documents Explores Manhattan Project, Eisenhower’s Early Misgivings about First Nuclear Use, Curtis LeMay and the Firebombing of Tokyo, Debates over Japanese Surrender Terms, Atomic Targeting Decisions, and Lagging Awareness of Radiation Effects

Washington, D.C., August 4, 2020 –  To mark the 75th anniversary of the atomic bombings of Hiroshima and Nagasaki in August 1945, the National Security Archive is updating and reposting one of its most popular e-books of the past 25 years. 

While U.S. leaders hailed the bombings at the time and for many years afterwards for bringing the Pacific war to an end and saving untold thousands of American lives, that interpretation has since been seriously challenged.  Moreover, ethical questions have shrouded the bombings which caused terrible human losses and in succeeding decades fed a nuclear arms race with the Soviet Union and now Russia and others.

Three-quarters of a century on, Hiroshima and Nagasaki remain emblematic of the dangers and human costs of warfare, specifically the use of nuclear weapons.  Since these issues will be subjects of hot debate for many more years, the Archive has once again refreshed its compilation of declassified U.S. government documents and translated Japanese records that first appeared on these pages in 2005.

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Introduction

By William Burr

The 75th anniversary of the atomic bombings of Hiroshima and Nagasaki in August 1945 is an occasion for sober reflection. In Japan and elsewhere around the world, each anniversary is observed with great solemnity. The bombings were the first time that nuclear weapons had been detonated in combat operations.  They caused terrible human losses and destruction at the time and more deaths and sickness in the years ahead from the radiation effects. And the U.S. bombings hastened the Soviet Union’s atomic bomb project and have fed a big-power nuclear arms race to this day. Thankfully, nuclear weapons have not been exploded in war since 1945, perhaps owing to the taboo against their use shaped by the dropping of the bombs on Japan. 

Along with the ethical issues involved in the use of atomic and other mass casualty weapons, why the bombs were dropped in the first place has been the subject of sometimes heated debate. As with all events in human history, interpretations vary and readings of primary sources can lead to different conclusions.  Thus, the extent to which the bombings contributed to the end of World War II or the beginning of the Cold War remain live issues.  A significant contested question is whether, under the weight of a U.S. blockade and massive conventional bombing, the Japanese were ready to surrender before the bombs were dropped.  Also still debated is the impact of the Soviet declaration of war and invasion of Manchuria, compared to the atomic bombings, on the Japanese decision to surrender. Counterfactual issues are also disputed, for example whether there were alternatives to the atomic bombings, or would the Japanese have surrendered had a demonstration of the bomb been used to produced shock and awe. Moreover, the role of an invasion of Japan in U.S. planning remains a matter of debate, with some arguing that the bombings spared many thousands of American lives that otherwise would have been lost in an invasion.

Those and other questions will be subjects of discussion well into the indefinite future. Interested readers will continue to absorb the fascinating historical literature on the subject.  Some will want to read declassified primary sources so they can further develop their own thinking about the issues. Toward that end, in 2005, at the time of the 60th anniversary of the bombings, staff at the National Security Archive compiled and scanned a significant number of declassified U.S. government documents to make them more widely available. The documents cover multiple aspects of the bombings and their context.  Also included, to give a wider perspective, were translations of Japanese documents not widely available before.  Since 2005, the collection has been updated. This latest iteration of the collection includes corrections, a few minor revisions, and updated footnotes to take into account recently published secondary literature.

2015 Update

August 4, 2015 – A few months after the atomic bombings of Hiroshima and Nagasaki, General Dwight D.  Eisenhower commented during a social occasion “how he had hoped that the war might have ended without our having to use the atomic bomb.” This virtually unknown evidence from the diary of Robert P. Meiklejohn, an assistant to Ambassador W. Averell Harriman, published for the first time today by the National Security Archive, confirms that the future President Eisenhower had early misgivings about the first use of atomic weapons by the United States. General George C. Marshall is the only high-level official whose contemporaneous (pre-Hiroshima) doubts about using the weapons against cities are on record.

On the 70th anniversary of the bombing of Hiroshima on August 6, 1945, the National Security Archive updates its 2005 publication of the most comprehensive on-line collection of declassified U.S. government documents on the first use of the atomic bomb and the end of the war in the Pacific. This update presents previously unpublished material and translations of difficult-to-find records. Included are documents on the early stages of the U.S. atomic bomb project, Army Air Force General  Curtis LeMay’s report  on the firebombing of Tokyo (March 1945), Secretary of War Henry  Stimson’s requests  for modification of unconditional surrender terms,  Soviet documents  relating to the events, excerpts from the Robert P. Meiklejohn diaries mentioned above, and selections from the diaries of Walter J. Brown, special assistant to Secretary of State James Byrnes.

The original 2005 posting included a wide range of material, including formerly top secret "Magic" summaries of intercepted Japanese communications and the first-ever full translations from the Japanese of accounts of high level meetings and discussions in Tokyo leading to the Emperor’s decision to surrender. Also documented are U.S. decisions to target Japanese cities, pre-Hiroshima petitions by scientists questioning the military use of the A-bomb, proposals for demonstrating the effects of the bomb, debates over whether to modify unconditional surrender terms, reports from the bombing missions of Hiroshima and Nagasaki, and belated top-level awareness of the radiation effects of atomic weapons.

The documents can help readers to make up their own minds about long-standing controversies such as whether the first use of atomic weapons was justified, whether President Harry S. Truman had alternatives to atomic attacks for ending the war, and what the impact of the Soviet declaration of war on Japan was. Since the 1960s, when the declassification of important sources began, historians have engaged in vigorous debate over the bomb and the end of World War II. Drawing on sources at the National Archives and the Library of Congress as well as Japanese materials, this electronic briefing book includes key documents that historians of the events have relied upon to present their findings and advance their interpretations.

The Atomic Bomb and the End of World War II: A Collection of Primary Sources

Seventy years ago this month, the United States dropped atomic bombs on Hiroshima and Nagasaki, the Soviet Union declared war on Japan, and the Japanese government surrendered to the United States and its allies. The nuclear age had truly begun with the first military use of atomic weapons. With the material that follows, the National Security Archive publishes the most comprehensive on-line collection to date of declassified U.S. government documents on the atomic bomb and the end of the war in the Pacific. Besides material from the files of the Manhattan Project, this collection includes formerly “Top Secret Ultra” summaries and translations of Japanese diplomatic cable traffic intercepted under the “Magic” program. Moreover, the collection includes for the first time translations from Japanese sources of high level meetings and discussions in Tokyo, including the conferences when Emperor Hirohito authorized the final decision to surrender. [1]

Ever since the atomic bombs were exploded over Japanese cities, historians, social scientists, journalists, World War II veterans, and ordinary citizens have engaged in intense controversy about the events of August 1945. John Hersey’s  Hiroshima , first published in the New Yorker  in 1946 encouraged unsettled readers to question the bombings while church groups and some commentators, most prominently Norman Cousins, explicitly criticized them. Former Secretary of War Henry Stimson found the criticisms troubling and published an influential justification for the attacks in  Harper’s . [2] During the 1960s the availability of primary sources made historical research and writing possible and the debate became more vigorous. Historians Herbert Feis and Gar Alperovitz raised searching questions about the first use of nuclear weapons and their broader political and diplomatic implications. The controversy, especially the arguments made by Alperovitz and others about “atomic diplomacy” quickly became caught up in heated debates over Cold War “revisionism.” The controversy simmered over the years with major contributions by Martin Sherwin and Barton J. Bernstein but it became explosive during the mid-1990s when curators at the National Air and Space Museum met the wrath of the Air Force Association over a proposed historical exhibit on the Enola Gay. [3] The NASM exhibit was drastically scaled-down but historians and journalist continued to engage in the debate. Alperovitz, Bernstein, and Sherwin made new contributions as did other historians, social scientists, and journalists including Richard B. Frank, Herbert Bix, Sadao Asada, Kai Bird, Robert James Maddox, Sean Malloy, Robert P. Newman, Robert S. Norris, Tsuyoshi Hagesawa, and J. Samuel Walker. [4]

The continued controversy has revolved around the following, among other, questions:

• were the atomic strikes necessary primarily to avert an invasion of Japan in November 1945?
• Did Truman authorize the use of atomic bombs for diplomatic-political reasons-- to intimidate the Soviets--or was his major goal to force Japan to surrender and bring the war to an early end?
• If ending the war quickly was the most important motivation of Truman and his advisers to what extent did they see an “atomic diplomacy” capability as a “bonus”?
• To what extent did subsequent justification for the atomic bomb exaggerate or misuse wartime estimates for U.S. casualties stemming from an invasion of Japan?
• Were there alternatives to the use of the weapons? If there were, what were they and how plausible are they in retrospect? Why were alternatives not pursued?
• How did the U.S. government plan to use the bombs? What concepts did war planners use to select targets? To what extent were senior officials interested in looking at alternatives to urban targets? How familiar was President Truman with the concepts that led target planners chose major cities as targets?
• What did senior officials know about the effects of atomic bombs before they were first used. How much did top officials know about the radiation effects of the weapons?
• Did President Truman make a decision, in a robust sense, to use the bomb or did he inherit a decision that had already been made?
• Were the Japanese ready to surrender before the bombs were dropped? To what extent had Emperor Hirohito prolonged the war unnecessarily by not seizing opportunities for surrender?
• If the United States had been more flexible about the demand for “unconditional surrender” by explicitly or implicitly guaranteeing a constitutional monarchy would Japan have surrendered earlier than it did?
• How decisive was the atomic bombings to the Japanese decision to surrender?
• Was the bombing of Nagasaki unnecessary? To the extent that the atomic bombing was critically important to the Japanese decision to surrender would it have been enough to destroy one city?
• Would the Soviet declaration of war have been enough to compel Tokyo to admit defeat?
• Was the dropping of the atomic bombs morally justifiable?

This compilation will not attempt to answer these questions or use primary sources to stake out positions on any of them. Nor is it an attempt to substitute for the extraordinary rich literature on the atomic bombings and the end of World War II. Nor does it include any of the interviews, documents prepared after the events, and post-World War II correspondence, etc. that participants in the debate have brought to bear in framing their arguments. Originally this collection did not include documents on the origins and development of the Manhattan Project, although this updated posting includes some significant records for context. By providing access to a broad range of U.S. and Japanese documents, mainly from the spring and summer of 1945, interested readers can see for themselves the crucial source material that scholars have used to shape narrative accounts of the historical developments and to frame their arguments about the questions that have provoked controversy over the years. To help readers who are less familiar with the debates, commentary on some of the documents will point out, although far from comprehensively, some of the ways in which they have been interpreted. With direct access to the documents, readers may develop their own answers to the questions raised above. The documents may even provoke new questions.

Contributors to the historical controversy have deployed the documents selected here to support their arguments about the first use of nuclear weapons and the end of World War II. The editor has closely reviewed the footnotes and endnotes in a variety of articles and books and selected documents cited by participants on the various sides of the controversy. [5] While the editor has a point of view on the issues, to the greatest extent possible he has tried to not let that influence document selection, e.g., by selectively withholding or including documents that may buttress one point of view or the other. The task of compilation involved consultation of primary sources at the National Archives, mainly in Manhattan Project files held in the records of the Army Corps of Engineers, Record Group 77, but also in the archival records of the National Security Agency. Private collections were also important, such as the Henry L. Stimson Papers held at Yale University (although available on microfilm, for example, at the Library of Congress) and the papers of W. Averell Harriman at the Library of Congress. To a great extent the documents selected for this compilation have been declassified for years, even decades; the most recent declassifications were in the 1990s.

The U.S. documents cited here will be familiar to many knowledgeable readers on the Hiroshima-Nagasaki controversy and the history of the Manhattan Project. To provide a fuller picture of the transition from U.S.-Japanese antagonism to reconciliation, the editor has done what could be done within time and resource constraints to present information on the activities and points of view of Japanese policymakers and diplomats. This includes a number of formerly top secret summaries of intercepted Japanese diplomatic communications, which enable interested readers to form their own judgments about the direction of Japanese diplomacy in the weeks before the atomic bombings. Moreover, to shed light on the considerations that induced Japan’s surrender, this briefing book includes new translations of Japanese primary sources on crucial events, including accounts of the conferences on August 9 and 14, where Emperor Hirohito made decisions to accept Allied terms of surrender.

[ Editor’s Note: Originally prepared in July 2005 this posting has been updated, with new documents, changes in organization, and other editorial changes. As noted, some documents relating to the origins of the Manhattan Project have been included in addition to entries from the Robert P. Meiklejohn diaries and translations of a few Soviet documents, among other items. Moreover, recent significant contributions to the scholarly literature have been taken into account.]

I. Background on the U.S. Atomic Project

Documents 1A-C: Report of the Uranium Committee

1A . Arthur H. Compton, National Academy of Sciences Committee on Atomic Fission, to Frank Jewett, President, National Academy of Sciences, 17 May 1941, Secret

1B . Report to the President of the National Academy of Sciences by the Academy Committee on Uranium, 6 November 1941, Secret

1C . Vannevar Bush, Director, Office of Scientific Research and Development, to President Roosevelt, 27 November 1941, Secret

Source: National Archives, Records of the Office of Scientific Research and Development, Record Group 227 (hereinafter RG 227), Bush-Conant papers microfilm collection, Roll 1, Target 2, Folder 1, "S-1 Historical File, Section A (1940-1941)."

This set of documents concerns the work of the Uranium Committee of the National Academy of Sciences, an exploratory project that was the lead-up to the actual production effort undertaken by the Manhattan Project. The initial report, May 1941, showed how leading American scientists grappled with the potential of nuclear energy for military purposes. At the outset, three possibilities were envisioned: radiological warfare, a power source for submarines and ships, and explosives. To produce material for any of those purposes required a capability to separate uranium isotopes in order to produce fissionable U-235. Also necessary for those capabilities was the production of a nuclear chain reaction. At the time of the first report, various methods for producing a chain reaction were envisioned and money was being budgeted to try them out.

Later that year, the Uranium Committee completed its report and OSRD Chairman Vannevar Bush reported the findings to President Roosevelt: As Bush emphasized, the U.S. findings were more conservative than those in the British MAUD report: the bomb would be somewhat “less effective,” would take longer to produce, and at a higher cost. One of the report’s key findings was that a fission bomb of superlatively destructive power will result from bringing quickly together a sufficient mass of element U235.” That was a certainty, “as sure as any untried prediction based upon theory and experiment can be.” The critically important task was to develop ways and means to separate highly enriched uranium from uranium-238. To get production going, Bush wanted to establish a “carefully chosen engineering group to study plans for possible production.” This was the basis of the Top Policy Group, or the S-1 Committee, which Bush and James B. Conant quickly established. [6]

In its discussion of the effects of an atomic weapon, the committee considered both blast and radiological damage. With respect to the latter, “It is possible that the destructive effects on life caused by the intense radioactivity of the products of the explosion may be as important as those of the explosion itself.” This insight was overlooked when top officials of the Manhattan Project considered the targeting of Japan during 1945. [7]

Documents 2A-B: Going Ahead with the Bomb

2A : Vannevar Bush to President Roosevelt, 9 March 1942, with memo from Roosevelt attached, 11 March 1942, Secret

2B : Vannevar Bush to President Roosevelt, 16 December 1942, Secret (report not attached)

Sources: 2A: RG 227, Bush-Conant papers microfilm collection, Roll 1, Target 2, Folder 1, "S-1 Historical File, Section II (1941-1942): 2B: Bush-Conant papers, S-1 Historical File, Reports to and Conferences with the President (1942-1944)

The Manhattan Project never had an official charter establishing it and defining its mission, but these two documents are the functional equivalent of a charter, in terms of presidential approvals for the mission, not to mention for a huge budget. In a progress report, Bush told President Roosevelt that the bomb project was on a pilot plant basis, but not yet at the production stage. By the summer, once “production plants” would be at work, he proposed that the War Department take over the project. In reply, Roosevelt wrote a short memo endorsing Bush’s ideas as long as absolute secrecy could be maintained. According to Robert S. Norris, this was “the fateful decision” to turn over the atomic project to military control. [8]

Some months later, with the Manhattan Project already underway and under the direction of General Leslie Grove, Bush outlined to Roosevelt the effort necessary to produce six fission bombs. With the goal of having enough fissile material by the first half of 1945 to produce the bombs, Bush was worried that the Germans might get there first. Thus, he wanted Roosevelt’s instructions as to whether the project should be “vigorously pushed throughout.” Unlike the pilot plant proposal described above, Bush described a real production order for the bomb, at an estimated cost of a “serious figure”: $400 million, which was an optimistic projection given the eventual cost of $1.9 billion. To keep the secret, Bush wanted to avoid a “ruinous” appropriations request to Congress and asked Roosevelt to ask Congress for the necessary discretionary funds. Initialed by President Roosevelt (“VB OK FDR”), this may have been the closest that he came to a formal approval of the Manhattan Project.

Document 3 : Memorandum by Leslie R. Grove, “Policy Meeting, 5/5/43,” Top Secret

Source:  National Archives, Record Group 77, Records of the Army Corps of Engineers (hereinafter RG 77), Manhattan Engineering District (MED), Minutes of the Military Policy Meeting (5 May 1943), Correspondence (“Top Secret”) of the Manhattan Engineer District, 1942-1946, microfilm publication M1109 (Washington, D.C.: National Archives and Records Administration, 1980), Roll 3, Target 6, Folder 23, “Military Policy Committee, Minutes of Meetings”

Before the Manhattan Project had produced any weapons, senior U.S. government officials had Japanese targets in mind. Besides discussing programmatic matters (e.g., status of gaseous diffusion plants, heavy water production for reactors, and staffing at Las Alamos), the participants agreed that the first use could be Japanese naval forces concentrated at Truk Harbor, an atoll in the Caroline Islands. If there was a misfire the weapon would be difficult for the Japanese to recover, which would not be the case if Tokyo was targeted. Targeting Germany was rejected because the Germans were considered more likely to “secure knowledge” from a defective weapon than the Japanese. That is, the United States could possibly be in danger if the Nazis acquired more knowledge about how to build a bomb. [9]

Document 4 :   Memo from General Groves to the Chief of Staff [Marshall], “Atomic Fission Bombs – Present Status and Expected Progress,” 7 August 1944, Top Secret, excised copy

Source: RG 77, Correspondence ("Top Secret") of the Manhattan Engineer District, 1942-1946, file 25M

This memorandum from General Groves to General Marshall captured how far the Manhattan Project had come in less than two years since Bush’s December 1942 report to President Roosevelt .  Groves did not mention this but around the time he wrote this the Manhattan Project had working at its far-flung installations over  125,000 people  ; taking into account high labor turnover some 485,000 people worked on the project (1 out of every 250 people in the country at that time). What these people were laboring to construct, directly or indirectly, were two types of weapons—a gun-type weapon using U-235 and an implosion weapon using plutonium (although the possibility of U-235 was also under consideration). As the scientists had learned, a gun-type weapon based on plutonium was “impossible” because that element had an “unexpected property”: spontaneous neutron emissions would cause the weapon to “fizzle.” [10]  For both the gun-type and the implosion weapons, a production schedule had been established and both would be available during 1945. The discussion of weapons effects centered on blast damage models; radiation and other effects were overlooked.

Document 5 : Memorandum from Vannevar Bush and James B. Conant, Office of Scientific Research and Development, to Secretary of War, September 30, 1944, Top Secret

Source: RG 77, Harrison-Bundy Files (H-B Files), folder 69 (copy from microfilm)

While Groves worried about the engineering and production problems, key War Department advisers were becoming troubled over the diplomatic and political implications of these enormously powerful weapons and the dangers of a global nuclear arms race. Concerned that President Roosevelt had an overly “cavalier” belief about the possibility of maintaining a post-war Anglo-American atomic monopoly, Bush and Conant recognized the limits of secrecy and wanted to disabuse senior officials of the notion that an atomic monopoly was possible. To suggest alternatives, they drafted this memorandum about the importance of the international exchange of information and international inspection to stem dangerous nuclear competition. [11]

Documents 6A-D: President Truman Learns the Secret:

6A : Memorandum for the Secretary of War from General L. R. Groves, “Atomic Fission Bombs,” April 23, 1945

6B : Memorandum discussed with the President, April 25, 1945

6C : [Untitled memorandum by General L.R. Groves, April 25, 1945

6D : Diary Entry, April 25, 1945

Sources: A: RG 77, Commanding General’s file no. 24, tab D; B: Henry Stimson Diary, Sterling Library, Yale University (microfilm at Library of Congress); C: Source: Record Group 200, Papers of General Leslie R. Groves, Correspondence 1941-1970, box 3, “F”; D: Henry Stimson Diary, Sterling Library, Yale University (microfilm at Library of Congress)

Soon after he was sworn in as president following President Roosevelt’s death, Harry Truman learned about the top secret Manhattan Project from a briefing from Secretary of War Stimson and Manhattan Project chief General Groves, who went through the “back door” to escape the watchful press. Stimson, who later wrote up the meeting in his diary, also prepared a discussion paper, which raised broader policy issues associated with the imminent possession of “the most terrible weapon ever known in human history.” In a background report prepared for the meeting, Groves provided a detailed overview of the bomb project from the raw materials to processing nuclear fuel to assembling the weapons to plans for using them, which were starting to crystallize.

With respect to the point about assembling the weapons, the first gun-type weapon “should be ready about 1 August 1945” while an implosion weapon would also be available that month. “The target is and was always expected to be Japan.” The question whether Truman “inherited assumptions” from the Roosevelt administration that that the bomb would be used has been a controversial one. Alperovitz and Sherwin have argued that Truman made “a real decision” to use the bomb on Japan by choosing “between various forms of diplomacy and warfare.” In contrast, Bernstein found that Truman “never questioned [the] assumption” that the bomb would and should be used. Norris also noted that “Truman’s `decision’ was a decision not to override previous plans to use the bomb.” [12]

II. Targeting Japan

Document 7 : Commander F. L. Ashworth to Major General L.R. Groves, “The Base of Operations of the 509 th  Composite Group,” February 24, 1945, Top Secret

Source: RG 77, MED Records, Top Secret Documents, File no. 5g

The force of B-29 nuclear delivery vehicles that was being readied for first nuclear use—the Army Air Force’s 509 th  Composite Group—required an operational base in the Western Pacific. In late February 1945, months before atomic bombs were ready for use, the high command selected Tinian, an island in the Northern Marianas Islands, for that base.

Document 8 : Headquarters XXI Bomber Command, “Tactical Mission Report, Mission No. 40 Flown 10 March 1945,”n.d., Secret

Source: Library of Congress, Curtis LeMay Papers, Box B-36

As part of the war with Japan, the Army Air Force waged a campaign to destroy major industrial centers with incendiary bombs. This document is General Curtis LeMay’s report on the firebombing of Tokyo--“the most destructive air raid in history”--which burned down over 16 square miles of the city, killed up to 100,000 civilians (the official figure was 83,793), injured more than 40,000, and made over 1 million homeless.  [13]  According to the “Foreword,” the purpose of the raid, which dropped 1,665 tons of incendiary bombs, was to destroy industrial and strategic targets “ not  to bomb indiscriminately civilian populations.” Air Force planners, however, did not distinguish civilian workers from the industrial and strategic structures that they were trying to destroy.

The killing of workers in the urban-industrial sector was one of the explicit goals of the air campaign against Japanese cities. According to a Joint Chiefs of Staff report on Japanese target systems, expected results from the bombing campaign included: “The absorption of man-hours in repair and relief; the dislocation of labor by casualty; the interruption of public services necessary to production, and above all the destruction of factories engaged in war industry.” While Stimson would later raise questions about the bombing of Japanese cities, he was largely disengaged from the details (as he was with atomic targeting). [14]

Firebombing raids on other cities followed Tokyo, including Osaka, Kobe, Yokahama, and Nagoya, but with fewer casualties (many civilians had fled the cities). For some historians, the urban fire-bombing strategy facilitated atomic targeting by creating a “new moral context,” in which earlier proscriptions against intentional targeting of civilians had eroded. [15]

Document 9 : Notes on Initial Meeting of Target Committee, May 2, 1945, Top Secret

Source: RG 77, MED Records, Top Secret Documents, File no. 5d (copy from microfilm)

On 27 April, military officers and nuclear scientists met to discuss bombing techniques, criteria for target selection, and overall mission requirements. The discussion of “available targets” included Hiroshima, the “largest untouched target not on the 21 st  Bomber Command priority list.” But other targets were under consideration, including Yawata (northern Kyushu), Yokohama, and Tokyo (even though it was practically “rubble.”) The problem was that the Air Force had a policy of “laying waste” to Japan’s cities which created tension with the objective of reserving some urban targets for nuclear destruction.  [16]

Document 10 : Memorandum from J. R. Oppenheimer to Brigadier General Farrell, May 11, 1945

Source: RG 77, MED Records, Top Secret Documents, File no. 5g (copy from microfilm)

As director of Los Alamos Laboratory, Oppenheimer’s priority was producing a deliverable bomb, but not so much the effects of the weapon on the people at the target. In keeping with General Groves’ emphasis on compartmentalization, the Manhattan Project experts on the effects of radiation on human biology were at the MetLab and other offices and had no interaction with the production and targeting units. In this short memorandum to Groves’ deputy, General Farrell, Oppenheimer explained the need for precautions because of the radiological dangers of a nuclear detonation. The initial radiation from the detonation would be fatal within a radius of about 6/10ths of a mile and “injurious” within a radius of a mile. The point was to keep the bombing mission crew safe; concern about radiation effects had no impact on targeting decisions.  [17]

Document 11 : Memorandum from Major J. A. Derry and Dr. N.F. Ramsey to General L.R. Groves, “Summary of Target Committee Meetings on 10 and 11 May 1945,” May 12, 1945, Top Secret

Scientists and officers held further discussion of bombing mission requirements, including height of detonation, weather, radiation effects (Oppenheimer’s memo), plans for possible mission abort, and the various aspects of target selection, including priority cities (“a large urban area of more than three miles diameter”) and psychological dimension. As for target cities, the committee agreed that the following should be exempt from Army Air Force bombing so they would be available for nuclear targeting: Kyoto, Hiroshima, Yokohama, and Kokura Arsenal. Japan’s cultural capital, Kyoto, would not stay on the list. Pressure from Secretary of War Stimson had already taken Kyoto off the list of targets for incendiary bombings and he would successfully object to the atomic bombing of that city.  [18]

Document 12 : Stimson Diary Entries, May 14 and 15, 1945

Source: Henry Stimson Diary, Sterling Library, Yale University (microfilm at Library of Congress)

On May 14 and 15, Stimson had several conversations involving S-1 (the atomic bomb); during a talk with Assistant Secretary of War John J. McCloy, he estimated that possession of the bomb gave Washington a tremendous advantage—“held all the cards,” a “royal straight flush”-- in dealing with Moscow on post-war problems: “They can’t get along without our help and industries and we have coming into action a weapon which will be unique.” The next day a discussion of divergences with Moscow over the Far East made Stimson wonder whether the atomic bomb would be ready when Truman met with Stalin in July. If it was, he believed that the bomb would be the “master card” in U.S. diplomacy. This and other entries from the Stimson diary (as well as the entry from the Davies diary that follows) are important to arguments developed by Gar Alperovitz and Barton J. Bernstein, among others, although with significantly different emphases, that in light of controversies with the Soviet Union over Eastern Europe and other areas, top officials in the Truman administration believed that possessing the atomic bomb would provide them with significant leverage for inducing Moscow’s acquiescence in U.S. objectives. [19]

Document 13 : Davies Diary entry for May 21, 1945

Source: Joseph E. Davies Papers, Library of Congress, box 17, 21 May 1945

While officials at the Pentagon continued to look closely at the problem of atomic targets, President Truman, like Stimson, was thinking about the diplomatic implications of the bomb. During a conversation with Joseph E. Davies, a prominent Washington lawyer and former ambassador to the Soviet Union, Truman said that he wanted to delay talks with Stalin and Churchill until July when the first atomic device had been tested. Alperovitz treated this entry as evidence in support of the atomic diplomacy argument, but other historians, ranging from Robert Maddox to Gabriel Kolko, have denied that the timing of the Potsdam conference had anything to do with the goal of using the bomb to intimidate the Soviets. [20]

Document 14 : Letter, O. C. Brewster to President Truman, 24 May 1945, with note from Stimson to Marshall, 30 May 1945, attached, secret

Source: Harrison-Bundy Files relating to the Development of the Atomic Bomb, 1942-1946, microfilm publication M1108 (Washington, D.C.: National Archives and Records Administration, 1980), File 77: "Interim Committee - International Control."

In what Stimson called the “letter of an honest man,” Oswald C. Brewster sent President Truman a profound analysis of the danger and unfeasibility of a U.S. atomic monopoly.  [21]  An engineer for the Kellex Corporation, which was involved in the gas diffusion project to enrich uranium, Brewster recognized that the objective was fissile material for a weapon. That goal, he feared, raised terrifying prospects with implications for the “inevitable destruction of our present day civilization.” Once the U.S. had used the bomb in combat other great powers would not tolerate a monopoly by any nation and the sole possessor would be “be the most hated and feared nation on earth.” Even the U.S.’s closest allies would want the bomb because “how could they know where our friendship might be five, ten, or twenty years hence.” Nuclear proliferation and arms races would be certain unless the U.S. worked toward international supervision and inspection of nuclear plants.

Brewster suggested that Japan could be used as a “target” for a “demonstration” of the bomb, which he did not further define. His implicit preference, however, was for non-use; he wrote that it would be better to take U.S. casualties in “conquering Japan” than “to bring upon the world the tragedy of unrestrained competitive production of this material.”

Document 15 : Minutes of Third Target Committee Meeting – Washington, May 28, 1945, Top Secret

More updates on training missions, target selection, and conditions required for successful detonation over the target. The target would be a city--either Hiroshima, Kyoto (still on the list), or Niigata--but specific “aiming points” would not be specified at that time nor would industrial “pin point” targets because they were likely to be on the “fringes” a city. The bomb would be dropped in the city’s center. “Pumpkins” referred to bright orange, pumpkin-shaped high explosive bombs—shaped like the “Fat Man” implosion weapon--used for bombing run test missions.

Document 16 : General Lauris Norstad to Commanding General, XXI Bomber Command, “509 th  Composite Group; Special Functions,” May 29, 1945, Top Secret

The 509 th  Composite Group’s cover story for its secret mission was the preparation of “Pumpkins” for use in battle. In this memorandum, Norstad reviewed the complex requirements for preparing B-29s and their crew for successful nuclear strikes.

Document 17 : Assistant Secretary of War John J. McCloy, “Memorandum of Conversation with General Marshal May 29, 1945 – 11:45 p.m.,” Top Secret

Source: Record Group 107, Office of the Secretary of War, Formerly Top Secret Correspondence of Secretary of War Stimson (“Safe File”), July 1940-September 1945, box 12, S-1

Tacitly dissenting from the Targeting Committee’s recommendations, Army Chief of Staff George Marshall argued for initial nuclear use against a clear-cut military target such as a “large naval installation.” If that did not work, manufacturing areas could be targeted, but only after warning their inhabitants. Marshall noted the “opprobrium which might follow from an ill considered employment of such force.” This document has played a role in arguments developed by Barton J. Bernstein that figures such as Marshall and Stimson were “caught between an older morality that opposed the intentional killing of non-combatants and a newer one that stressed virtually total war.” [22]  

Document 18 : “Notes of the Interim Committee Meeting Thursday, 31 May 1945, 10:00 A.M. to 1:15 P.M. – 2:15 P.M. to 4:15 P.M., ” n.d., Top Secret

Source: RG 77, MED Records, H-B files, folder no. 100 (copy from microfilm)

With Secretary of War Stimson presiding, members of the committee heard reports on a variety of Manhattan Project issues, including the stages of development of the atomic project, problems of secrecy, the possibility of informing the Soviet Union, cooperation with “like-minded” powers, the military impact of the bomb on Japan, and the problem of “undesirable scientists.” Interested in producing the “greatest psychological effect,” the Committee members agreed that the “most desirable target would be a vital war plant employing a large number of workers and closely surrounded by workers’ houses.” Exactly how the mass deaths of civilians would persuade Japanese rulers to surrender was not discussed. Bernstein has argued that this target choice represented an uneasy endorsement of “terror bombing”--the target was not exclusively military or civilian; nevertheless, worker’s housing would include non-combatant men, women, and children. [23]  It is possible that Truman was informed of such discussions and their conclusions, although he clung to a belief that the prospective targets were strictly military.

Document 19 : General George A. Lincoln to General Hull, June 4, 1945, enclosing draft, Top Secret

Source: Record Group 165, Records of the War Department General and Special Staffs, American-British-Canadian Top Secret Correspondence, Box 504, “ABC 387 Japan (15 Feb. 45)

George A. Lincoln, chief of the Strategy and Policy Group at U.S. Army’s Operations Department, commented on a memorandum by former President Herbert Hoover that Stimson had passed on for analysis. Hoover proposed a compromise solution with Japan that would allow Tokyo to retain part of its empire in East Asia (including Korea and Japan) as a way to head off Soviet influence in the region. While Lincoln believed that the proposed peace teams were militarily acceptable he doubted that they were workable or that they could check Soviet “expansion” which he saw as an inescapable result of World War II. As to how the war with Japan would end, he saw it as “unpredictable,” but speculated that “it will take Russian entry into the war, combined with a landing, or imminent threat of a landing, on Japan proper by us, to convince them of the hopelessness of their situation.” Lincoln derided Hoover’s casualty estimate of 500,000. J. Samuel Walker has cited this document to make the point that “contrary to revisionist assertions, American policymakers in the summer of 1945 were far from certain that the Soviet invasion of Manchuria would be enough in itself to force a Japanese surrender.”  [24]

Document 20 : Memorandum from R. Gordon Arneson, Interim Committee Secretary, to Mr. Harrison, June 6, 1945, Top Secret

In a memorandum to George Harrison, Stimson’s special assistant on Manhattan Project matters, Arneson noted actions taken at the recent Interim Committee meetings, including target criterion and an attack “without prior warning.”

Document 21 : Memorandum of Conference with the President, June 6, 1945, Top Secret

Source: Henry Stimson Papers, Sterling Library, Yale University (microfilm at Library of Congress)

Stimson and Truman began this meeting by discussing how they should handle a conflict with French President DeGaulle over the movement by French forces into Italian territory. (Truman finally cut off military aid to France to compel the French to pull back).  [25]  As evident from the discussion, Stimson strongly disliked de Gaulle whom he regarded as “psychopathic.” The conversation soon turned to the atomic bomb, with some discussion about plans to inform the Soviets but only after a successful test. Both agreed that the possibility of a nuclear “partnership” with Moscow would depend on “quid pro quos”: “the settlement of the Polish, Rumanian, Yugoslavian, and Manchurian problems.”

At the end, Stimson shared his doubts about targeting cities and killing civilians through area bombing because of its impact on the U.S.’s reputation as well as on the problem of finding targets for the atomic bomb. Barton Bernstein has also pointed to this as additional evidence of the influence on Stimson of an “an older morality.” While concerned about the U.S.’s reputation, Stimson did not want the Air Force to bomb Japanese cities so thoroughly that the “new weapon would not have a fair background to show its strength,” a comment that made Truman laugh.  The discussion of “area bombing” may have reminded him that Japanese civilians remained at risk from U.S. bombing operations.

III. Debates on Alternatives to First Use and Unconditional Surrender

Document 22 : Memorandum from Arthur B. Compton to the Secretary of War, enclosing “Memorandum on `Political and Social Problems,’ from Members of the `Metallurgical Laboratory’ of the University of Chicago,” June 12, 1945, Secret

Source: RG 77, MED Records, H-B files, folder no. 76 (copy from microfilm)

Physicists Leo Szilard and James Franck, a Nobel Prize winner, were on the staff of the “Metallurgical Laboratory” at the University of Chicago, a cover for the Manhattan Project program to produce fuel for the bomb. The outspoken Szilard was not involved in operational work on the bomb and General Groves kept him under surveillance but Met Lab director Arthur Compton found Szilard useful to have around. Concerned with the long-run implications of the bomb, Franck chaired a committee, in which Szilard and Eugene Rabinowitch were major contributors, that produced a report rejecting a surprise attack on Japan and recommended instead a demonstration of the bomb on the “desert or a barren island.” Arguing that a nuclear arms race “will be on in earnest not later than the morning after our first demonstration of the existence of nuclear weapons,” the committee saw international control as the alternative. That possibility would be difficult if the United States made first military use of the weapon. Compton raised doubts about the recommendations but urged Stimson to study the report. Martin Sherwin has argued that the Franck committee shared an important assumption with Truman et al.--that an “atomic attack against Japan would `shock’ the Russians”--but drew entirely different conclusions about the import of such a shock.  [26]

Document 23 : Memorandum from Acting Secretary of State Joseph Grew to the President, “Analysis of Memorandum Presented by Mr. Hoover,” June 13, 1945

Source: Record Group 107, Office of the Secretary of War, Formerly Top Secret Correspondence of Secretary of War Stimson (“Safe File”), July 1940-September 1945, box 8, Japan (After December 7/41)

A former ambassador to Japan, Joseph Grew’s extensive knowledge of Japanese politics and culture informed his stance toward the concept of unconditional surrender. He believed it essential that the United States declare its intention to preserve the institution of the emperor. As he argued in this memorandum to President Truman, “failure on our part to clarify our intentions” on the status of the emperor “will insure prolongation of the war and cost a large number of human lives.” Documents like this have played a role in arguments developed by Alperovitz that Truman and his advisers had alternatives to using the bomb such as modifying unconditional surrender and that anti-Soviet considerations weighed most heavily in their thinking. By contrast, Herbert P. Bix has suggested that the Japanese leadership would “probably not” have surrendered if the Truman administration had spelled out the status of the emperor. [27]

Document 24 : Memorandum from Chief of Staff Marshall to the Secretary of War, 15 June 1945, enclosing “Memorandum of Comments on `Ending the Japanese War,’” prepared by George A. Lincoln, June 14, 1945, Top Secret

Commenting on another memorandum by Herbert Hoover, George A. Lincoln discussed war aims, face-saving proposals for Japan, and the nature of the proposed declaration to the Japanese government, including the problem of defining “unconditional surrender.” Lincoln argued against modifying the concept of unconditional surrender: if it is “phrased so as to invite negotiation” he saw risks of prolonging the war or a “compromise peace.” J. Samuel Walker has observed that those risks help explain why senior officials were unwilling to modify the demand for unconditional surrender. [28]

Document 25 : Memorandum by J. R. Oppenheimer, “Recommendations on the Immediate Use of Nuclear Weapons,” June 16, 1945, Top Secret

In a report to Stimson, Oppenheimer and colleagues on the scientific advisory panel--Arthur Compton, Ernest O. Lawrence, and Enrico Fermi—tacitly disagreed with the report of the “Met Lab” scientists. The panel argued for early military use but not before informing key allies about the atomic project to open a dialogue on “how we can cooperate in making this development contribute to improved international relations.”

Document 26 : “Minutes of Meeting Held at the White House on Monday, 18 June 1945 at 1530,” Top Secret

Source: Record Group 218, Records of the Joint Chiefs of Staff, Central Decimal Files, 1942-1945, box 198 334 JCS (2-2-45) Mtg 186 th -194 th

With the devastating battle for Okinawa winding up, Truman and the Joint Chiefs stepped back and considered what it would take to secure Japan’s surrender. The discussion depicted a Japan that, by 1 November, would be close to defeat, with great destruction and economic losses produced by aerial bombing and naval blockade, but not ready to capitulate. Marshall believed that the latter required Soviet entry and an invasion of Kyushu, even suggesting that Soviet entry might be the “decisive action levering them into capitulation.” Truman and the Chiefs reviewed plans to land troops on Kyushu on 1 November, which Marshall believed was essential because air power was not decisive. He believed that casualties would not be more than those produced by the battle for Luzon, some 31,000. This account hints at discussion of the atomic bomb (“certain other matters”), but no documents disclose that part of the meeting.

The record of this meeting has figured in the complex debate over the estimates of casualties stemming from a possible invasion of Japan. While post-war justifications for the bomb suggested that an invasion of Japan could have produced very high levels of casualties (dead, wounded, or missing), from hundreds of thousands to a million, historians have vigorously debated the extent to which the estimates were inflated.  [29]

According to accounts based on post-war recollections and interviews, during the meeting McCloy raised the possibility of winding up the war by guaranteeing the preservation of the emperor albeit as a constitutional monarch. If that failed to persuade Tokyo, he proposed that the United States disclose the secret of the atomic bomb to secure Japan’s unconditional surrender. While McCloy later recalled that Truman expressed interest, he said that Secretary of State Byrnes squashed the proposal because of his opposition to any “deals” with Japan. Yet, according to Forrest Pogue’s account, when Truman asked McCloy if he had any comments, the latter opened up a discussion of nuclear weapons use by asking “Why not use the bomb?” [30]

Document 27 : Memorandum from R. Gordon Arneson, Interim Committee Secretary, to Mr. Harrison, June 25, 1945, Top Secret

For Harrison’s convenience, Arneson summarized key decisions made at the 21 June meeting of the Interim Committee, including a recommendation that President Truman use the forthcoming conference of allied leaders to inform Stalin about the atomic project. The Committee also reaffirmed earlier recommendations about the use of the bomb at the “earliest opportunity” against “dual targets.” In addition, Arneson included the Committee’s recommendation for revoking part two of the 1944 Quebec agreement which stipulated that the neither the United States nor Great Britain would use the bomb “against third parties without each other’s consent.” Thus, an impulse for unilateral control of nuclear use decisions predated the first use of the bomb.

Document 28 : Memorandum from George L. Harrison to Secretary of War, June 26, 1945, Top Secret

Source: RG 77, MED, H-B files, folder no. 77 (copy from microfilm)

Reminding Stimson about the objections of some Manhattan project scientists to military use of the bomb, Harrison summarized the basic arguments of the Franck report. One recommendation shared by many of the scientists, whether they supported the report or not, was that the United States inform Stalin of the bomb before it was used. This proposal had been the subject of positive discussion by the Interim Committee on the grounds that Soviet confidence was necessary to make possible post-war cooperation on atomic energy.

Document 29 : Memorandum from George L. Harrison to Secretary of War, June 28, 1945, Top Secret, enclosing Ralph Bard’s “Memorandum on the Use of S-1 Bomb,” June 27, 1945

Under Secretary of the Navy Ralph Bard joined those scientists who sought to avoid military use of the bomb; he proposed a “preliminary warning” so that the United States would retain its position as a “great humanitarian nation.” Alperovitz cites evidence that Bard discussed his proposal with Truman who told him that he had already thoroughly examined the problem of advanced warning. This document has also figured in the argument framed by Barton Bernstein that Truman and his advisers took it for granted that the bomb was a legitimate weapon and that there was no reason to explore alternatives to military use. Bernstein, however, notes that Bard later denied that he had a meeting with Truman and that White House appointment logs support that claim. [31]

Document 30 : Memorandum for Mr. McCloy, “Comments re: Proposed Program for Japan,” June 28, 1945, Draft, Top Secret

Source: RG 107, Office of Assistant Secretary of War Formerly Classified Correspondence of John J. McCloy, 1941-1945, box 38, ASW 387 Japan

Despite the interest of some senior officials such as Joseph Grew, Henry Stimson, and John J. McCloy in modifying the concept of unconditional surrender so that the Japanese could be sure that the emperor would be preserved, it remained a highly contentious subject. For example, one of McCloy’s aides, Colonel Fahey, argued against modification of unconditional surrender (see “Appendix ‘C`”).

Document 31 : Assistant Secretary of War John J. McCloy to Colonel Stimson, June 29, 1945, Top Secret

McCloy was part of a drafting committee at work on the text of a proclamation to Japan to be signed by heads of state at the forthcoming Potsdam conference. As McCloy observed the most contentious issue was whether the proclamation should include language about the preservation of the emperor: “This may cause repercussions at home but without it those who seem to know the most about Japan feel there would be very little likelihood of acceptance.”

Document 32 : Memorandum, “Timing of Proposed Demand for Japanese Surrender,” June 29, 1945, Top Secret

Probably the work of General George A. Lincoln at Army Operations, this document was prepared a few weeks before the Potsdam conference when senior officials were starting to finalize the text of the declaration that Truman, Churchill, and Chiang would issue there. The author recommended issuing the declaration “just before the bombardment program [against Japan] reaches its peak.” Next to that suggestion, Stimson or someone in his immediate office, wrote “S1”, implying that the atomic bombing of Japanese cities was highly relevant to the timing issue. Also relevant to Japanese thinking about surrender, the author speculated, was the Soviet attack on their forces after a declaration of war.

Document 33 : Stimson memorandum to The President, “Proposed Program for Japan,” 2 July 1945, Top Secret

Source: Naval Aide to the President Files, box 4, Berlin Conference File, Volume XI - Miscellaneous papers: Japan, Harry S. Truman Presidential Library

On 2 July Stimson presented to President Truman a proposal that he had worked up with colleagues in the War Department, including McCloy, Marshall, and Grew. The proposal has been characterized as “the most comprehensive attempt by any American policymaker to leverage diplomacy” in order to shorten the Pacific War. Stimson had in mind a “carefully timed warning” delivered before the invasion of Japan. Some of the key elements of Stimson’s argument were his assumption that “Japan is susceptible to reason” and that Japanese might be even more inclined to surrender if “we do not exclude a constitutional monarchy under her present dynasty.” The possibility of a Soviet attack would be part of the “threat.” As part of the threat message, Stimson alluded to the “inevitability and completeness of the destruction” which Japan could suffer, but he did not make it clear whether unconditional surrender terms should be clarified before using the atomic bomb. Truman read Stimson’s proposal, which he said was “powerful,” but made no commitments to the details, e.g., the position of the emperor.  [32]

Document 34 : Minutes, Secretary’s Staff Committee, Saturday Morning, July 7, 1945, 133d Meeting, Top Secret

Source: Record Group 353, Records of Interdepartmental and Intradepartmental Committees, Secretary’s Staff Meetings Minutes, 1944-1947 (copy from microfilm)

The possibility of modifying the concept of unconditional surrender so that it guaranteed the continuation of the emperor remained hotly contested within the U.S. government. Here senior State Department officials, Under Secretary Joseph Grew on one side, and Assistant Secretary Dean Acheson and Archibald MacLeish on the other, engaged in hot debate.

Document 35 : Combined Chiefs of Staff, “Estimate of the Enemy Situation (as of 6 July 1945, C.C.S 643/3, July 8, 1945, Secret (Appendices Not Included)

Source: RG 218, Central Decimal Files, 1943-1945, CCS 381 (6-4-45), Sec. 2 Pt. 5

This review of Japanese capabilities and intentions portrays an economy and society under “tremendous strain”; nevertheless, “the ground component of the Japanese armed forces remains Japan’s greatest military asset.” Alperovitz sees statements in this estimate about the impact of Soviet entry into the war and the possibility of a conditional surrender involving survival of the emperor as an institution as more evidence that the policymakers saw alternatives to nuclear weapons use. By contrast, Richard Frank takes note of the estimate’s depiction of the Japanese army’s terms for peace: “for surrender to be acceptable to the Japanese army it would be necessary for the military leaders to believe that it would not entail discrediting the warrior tradition and that it would permit the ultimate resurgence of a military in Japan.” That, Frank argues, would have been “unacceptable to any Allied policy maker.” [33]

Document 36 : Cable to Secretary of State from Acting Secretary Joseph Grew, July 16, 1945, Top Secret

Source: Record Group 59, Decimal Files 1945-1949, 740.0011 PW (PE)/7-1645

On the eve of the Potsdam Conference, a State Department draft of the proclamation to Japan contained language which modified unconditional surrender by promising to retain the emperor. When former Secretary of State Cordell Hull learned about it he outlined his objections to Byrnes, arguing that it might be better to wait “the climax of allied bombing and Russia’s entry into the war.” Byrnes was already inclined to reject that part of the draft, but Hull’s argument may have reinforced his decision.

Document 37 : Letter from Stimson to Byrnes, enclosing memorandum to the President, “The Conduct of the War with Japan,” 16 July 1945, Top Secret

Source: Henry L. Stimson Papers (MS 465), Sterling Library, Yale University (reel 113) (microfilm at Library of Congress)

Still interested in trying to find ways to “warn Japan into surrender,” this represents an attempt by Stimson before the Potsdam conference, to persuade Truman and Byrnes to agree to issue warnings to Japan prior to the use of the bomb. The warning would draw on the draft State-War proclamation to Japan; presumably, the one criticized by Hull (above) which included language about the emperor .  Presumably the clarified warning would be issued prior to the use of the bomb; if the Japanese persisted in fighting then “the full force of our new weapons should be brought to bear” and a “heavier” warning would be issued backed by the “actual entrance of the Russians in the war.” Possibly, as Malloy has argued, Stimson was motivated by concerns about using the bomb against civilians and cities, but his latest proposal would meet resistance at Potsdam from Byrnes and other. [34]

Document 38 : R. E. Lapp, Leo Szilard et al., “A Petition to the President of the United States,” July 17, 1945

On the eve of the Potsdam conference, Leo Szilard circulated a petition as part of a final effort to discourage military use of the bomb. Signed by about 68 Manhattan Project scientists, mainly physicists and biologists (copies with the remaining signatures are in the archival file), the petition did not explicitly reject military use, but raised questions about an arms race that military use could instigate and requested Truman to publicize detailed terms for Japanese surrender. Truman, already on his way to Europe, never saw the petition. [35]

IV. The Japanese Search for Soviet Mediation

Documents 39A-B: Magic

39A : William F. Friedman, Consultant (Armed Forces Security Agency), “A Short History of U.S. COMINT Activities,” 19 February 1952, Top Secret

39B :“Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1204 – July 12, 1945, Top Secret Ultra

Sources: A: National Security Agency Mandatory declassification review release; B: Record Group 457, Records of the National Security Agency/Central Security Service, “Magic” Diplomatic Summaries 1942-1945, box 18

Beginning in September 1940, U.S. military intelligence began to decrypt routinely, under the “Purple” code-name, the intercepted cable traffic of the Japanese Foreign Ministry. Collectively the decoded messages were known as “Magic.” How this came about is explained in an internal history of pre-war and World War II Army and Navy code-breaking activities prepared by  William F. Friedman , a central figure in the development of U.S. government cryptology during the 20 th  century. The National Security Agency kept the ‘Magic” diplomatic and military summaries classified for many years and did not release the entire series for 1942 through August 1945 until the early 1990s. [36]

The 12 July 1945 “Magic” summary includes a report on a cable from Japanese Foreign Minister Shigenori Togo to Ambassador Naotake Sato in Moscow concerning the Emperor’s decision to seek Soviet help in ending the war. Not knowing that the Soviets had already made a commitment to their Allies to declare war on Japan, Tokyo fruitlessly pursued this option for several weeks. The “Magic” intercepts from mid-July have figured in Gar Alperovitz’s argument that Truman and his advisers recognized that the Emperor was ready to capitulate if the Allies showed more flexibility on the demand for unconditional surrender. This point is central to Alperovitz’s thesis that top U.S. officials recognized a “two-step logic”: relaxing unconditional surrender and a Soviet declaration of war would have been enough to induce Japan’s surrender without the use of the bomb. [37]

Document 40 : John Weckerling, Deputy Assistant Chief of Staff, G-2, July 12, 1945, to Deputy Chief of Staff, “Japanese Peace Offer,” 13 July 1945, Top Secret Ultra

Source: RG 165, Army Operations OPD Executive File #17, Item 13 (copy courtesy of J. Samuel Walker)

The day after the Togo message was reported, Army intelligence chief Weckerling proposed several possible explanations of the Japanese diplomatic initiative. Robert J. Maddox has cited this document to support his argument that top U.S. officials recognized that Japan was not close to surrender because Japan was trying to “stave off defeat.” In a close analysis of this document, Tsuyoshi Hasegawa, who is also skeptical of claims that the Japanese had decided to surrender, argues that each of the three possibilities proposed by Weckerling “contained an element of truth, but none was entirely correct”. For example, the “governing clique” that supported the peace moves was not trying to “stave off defeat” but was seeking Soviet help to end the war. [38]

Document 41 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1205 – July 13, 1945, Top Secret Ultra

Source: Record Group 457, Records of the National Security Agency/Central Security Service, “Magic” Diplomatic Summaries 1942-1945, box 18

The day after he told Sato about the current thinking on Soviet mediation, Togo requested the Ambassador to see Soviet Foreign Minister Vyacheslav Molotov and tell him of the Emperor’s “private intention to send Prince Konoye as a Special Envoy” to Moscow. Before he received Togo’s message, Sato had already met with Molotov on another matter.

Document 42 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1210 – July 17, 1945, Top Secret Ultra

Source: Record Group 457, Records of the National Security Agency/Central Security Service, “Magic” Diplomatic Summaries 1942-1945, box 18.

Another intercept of a cable from Togo to Sato shows that the Foreign Minister rejected unconditional surrender and that the Emperor was not “asking the Russian’s mediation in anything like unconditional surrender.” Incidentally, this “`Magic’ Diplomatic Summary” indicates the broad scope and capabilities of the program; for example, it includes translations of intercepted French messages (see pages 8-9).

Document 43 : Admiral Tagaki Diary Entry for July 20, 1945

Source: Takashi Itoh, ed.,  Sokichi Takagi: Nikki to Joho  [Sokichi Takagi: Diary and Documents] (Tokyo, Japan: Misuzu-Shobo, 2000), 916-917 [Translation by Hikaru Tajima]

In 1944 Navy minister Mitsumasa Yonai ordered rear admiral Sokichi Takagi to go on sick leave so that he could undertake a secret mission to find a way to end the war. Tagaki was soon at the center of a cabal of Japanese defense officials, civil servants, and academics, which concluded that, in the end, the emperor would have to “impose his decision on the military and the government.” Takagi kept a detailed account of his activities, part of which was in diary form, the other part of which he kept on index cards. The material reproduced here gives a sense of the state of play of Foreign Minister Togo’s attempt to secure Soviet mediation. Hasegawa cited it and other documents to make a larger point about the inability of the Japanese government to agree on “concrete” proposals to negotiate an end to the war. [39]

The last item discusses Japanese contacts with representatives of the Office of Strategic Services (OSS) in Switzerland. The reference to “our contact” may refer to Bank of International Settlements economist Pers Jacobbson who was in touch with Japanese representatives to the Bank as well as Gero von Gävernitz, then on the staff, but with non-official cover, of OSS station chief Allen Dulles. The contacts never went far and Dulles never received encouragement to pursue them. [40]

V. The Trinity Test

Document 44 : Letter from Commissar of State Security First Rank, V. Merkulov, to People’s Commissar for Internal Affairs L. P. Beria, 10 July 1945, Number 4305/m, Top Secret (translation by Anna Melyaskova)

Source:  L.D. Riabev, ed.,  Atomnyi Proekt SSSR  (Moscow: izd MFTI, 2002), Volume 1, Part 2, 335-336

This 10 July 1945 letter from NKVD director V. N. Merkulov to Beria is an example of Soviet efforts to collect inside information on the Manhattan Project, although not all the detail was accurate. Merkulov reported that the United States had scheduled the test of a nuclear device for that same day, although the actual test took place 6 days later. According to Merkulov, two fissile materials were being produced: element-49 (plutonium), and U-235; the test device was fueled by plutonium. The Soviet source reported that the weight of the device was 3 tons (which was in the ball park) and forecast an explosive yield of 5 kilotons. That figure was based on underestimates by Manhattan Project scientists: the actual yield of the test device was 20 kilotons.

As indicated by the L.D. Riabev’s notes, it is possible that Beria’s copy of this letter ended up in Stalin’s papers. That the original copy is missing from Beria’s papers suggests that he may have passed it on to Stalin before the latter left for the Potsdam conference. [41]

Document 45 : Telegram War [Department] 33556, from Harrison to Secretary of War, July 17, 1945, Top Secret

Source: RG 77, MED Records, Top Secret Documents, File 5e (copy from microfilm)

An elated message from Harrison to Stimson reported the success of the  Trinity Test  of a plutonium implosion weapon. The light from the explosion could been seen “from here [Washington, D.C.] to “high hold” [Stimson’s estate on Long Island—250 miles away]” and it was so loud that Harrison could have heard the “screams” from Washington, D.C. to “my farm” [in Upperville, VA, 50 miles away] [42]

Document 46 : Memorandum from General L. R. Groves to Secretary of War, “The Test,” July 18, 1945, Top Secret, Excised Copy

Source: RG 77, MED Records, Top Secret Documents, File no. 4 (copy from microfilm)

General Groves prepared for Stimson, then at Potsdam, a detailed account of the Trinity test. [43]

VI. The Potsdam Conference

Document 47 : Truman’s Potsdam Diary

Source: Barton J. Bernstein, “Truman at Potsdam: His Secret Diary,”  Foreign Service Journal , July/August 1980, excerpts, used with author’s permission. [44]

Some years after Truman’s death, a hand-written diary that he kept during the Potsdam conference surfaced in his personal papers. For convenience, Barton Bernstein’s rendition is provided here but linked here are the scanned versions of Truman’s handwriting on the National Archives’ website (for 15-30 July).

The diary entries cover July 16, 17, 18, 20, 25, 26, and 30 and include Truman’s thinking about a number of issues and developments, including his reactions to Churchill and Stalin, the atomic bomb and how it should be targeted, the possible impact of the bomb and a Soviet declaration of war on Japan, and his decision to tell Stalin about the bomb. Receptive to pressure from Stimson, Truman recorded his decision to take Japan’s “old capital” (Kyoto) off the atomic bomb target list. Barton Bernstein and Richard Frank, among others, have argued that Truman’s assertion that the atomic targets were “military objectives” suggested that either he did not understand the power of the new weapons or had simply deceived himself about the nature of the targets. Another statement—“Fini Japs when that [Soviet entry] comes about”—has also been the subject of controversy over whether it meant that Truman thought it possible that the war could end without an invasion of Japan. [45]

Document 48 : Stimson Diary entries for July 16 through 25, 1945

Stimson did not always have Truman’s ear, but historians have frequently cited his diary when he was at the Potsdam conference. There Stimson kept track of S-1 developments, including news of the successful first test (see entry for July 16) and the ongoing deployments for nuclear use against Japan. When Truman received a detailed account of the test, Stimson reported that the “President was tremendously pepped up by it” and that “it gave him an entirely new feeling of confidence” (see entry for July 21). Whether this meant that Truman was getting ready for a confrontation with Stalin over Eastern Europe and other matters has also been the subject of debate.

An important question that Stimson discussed with Marshall, at Truman’s request, was whether Soviet entry into the war remained necessary to secure Tokyo’s surrender. Marshall was not sure whether that was so although Stimson privately believed that the atomic bomb would provide enough to force surrender (see entry for July 23). This entry has been cited by all sides of the controversy over whether Truman was trying to keep the Soviets out of the war. [46]  During the meeting on August 24, discussed above, Stimson gave his reasons for taking Kyoto off the atomic target list: destroying that city would have caused such “bitterness” that it could have become impossible “to reconcile the Japanese to us in that area rather than to the Russians.” Stimson vainly tried to preserve language in the Potsdam Declaration designed to assure the Japanese about “the continuance of their dynasty” but received Truman’s assurance that such a consideration could be conveyed later through diplomatic channels (see entry for July 24). Hasegawa argues that Truman realized that the Japanese would refuse a demand for unconditional surrender without a proviso on a constitutional monarchy and that “he needed Japan’s refusal to justify the use of the atomic bomb.” [47]

Document 49 : Walter Brown Diaries, July 10-August 3, 1945

Source: Clemson University Libraries, Special Collections, Clemson, SC; Mss 243, Walter J. Brown Papers, box 10, folder 12, Byrnes, James F.: Potsdam, Minutes, July-August 1945

Walter Brown, who served as special assistant to Secretary of State Byrnes, kept a diary which provided considerable detail on the Potsdam conference and the growing concerns about Soviet policy among top U.S. officials. This document is a typed-up version of the hand-written original (which Brown’s family has provided to Clemson University). That there may be a difference between the two sources becomes evident from some of the entries; for example, in the entry for July 18, 1945 Brown wrote: "Although I knew about the atomic bomb when I wrote these notes, I dared not place it in writing in my book.”

The degree to which the typed-up version reflects the original is worth investigating. In any event, historians have used information from the diary to support various interpretations. For example, Bernstein cites the entries for 20 and 24 July to argue that “American leaders did not view Soviet entry as a substitute for the bomb” but that the latter “would be so powerful, and the Soviet presence in Manchuria so militarily significant, that there was no need for actual Soviet intervention in the war.” For  Brown's diary entry of 3 August 9 1945 historians have developed conflicting interpretations (See discussion of document 57). [48]

Document 50 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1214 – July 22, 1945, Top Secret Ultra

This “Magic” summary includes messages from both Togo and Sato. In a long and impassioned message, the latter argued why Japan must accept defeat: “it is meaningless to prove one’s devotion [to the Emperor] by wrecking the State.” Togo rejected Sato’s advice that Japan could accept unconditional surrender with one qualification: the “preservation of the Imperial House.” Probably unable or unwilling to take a soft position in an official cable, Togo declared that “the whole country … will pit itself against the enemy in accordance with the Imperial Will as long as the enemy demands unconditional surrender.”

Document 51 : Forrestal Diary Entry, July 24, 1945, “Japanese Peace Feelers”

Source: Naval Historical Center, Operational Archives, James Forrestal Diaries

Secretary of the Navy James Forrestal was a regular recipient of “Magic” intercept reports; this substantial entry reviews the dramatic Sato-Togo exchanges covered in the 22 July “Magic” summary (although Forrestal misdated Sato’s cable as “first of July” instead of the 21 st ). In contrast to Alperovitz’s argument that Forrestal tried to modify the terms of unconditional surrender to give the Japanese an out, Frank sees Forrestal’s account of the Sato-Togo exchange as additional evidence that senior U.S. officials understood that Tokyo was not on the “cusp of surrender.”  [49]

Document 52 : Davies Diary entry for July 29, 1945

S ource: Joseph E. Davies Papers, Library of Congress, Manuscripts Division, box 19, 29 July 1945

Having been asked by Truman to join the delegation to the Potsdam conference, former-Ambassador Davies sat at the table with the Big Three throughout the discussions. This diary entry has figured in the argument that Byrnes believed that the atomic bomb gave the United States a significant advantage in negotiations with the Soviet Union. Plainly Davies thought otherwise. [50]

VII. Debates among the Japanese – Late July/Early August 1945

Document 53 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1221- July 29, 1945, Top Secret Ultra

In the  Potsdam Declaration  the governments of China, Great Britain, and the United States) demanded the “unconditional surrender of all Japanese armed forces. “The alternative is prompt and utter destruction.” The next day, in response to questions from journalists about the government’s reaction to the ultimatum, Prime Minister Suzuki apparently said that “We can only ignore [ mokusatsu ] it. We will do our utmost to complete the war to the bitter end.” That, Bix argues, represents a “missed opportunity” to end the war and spare the Japanese from continued U.S. aerial attacks. [51]  Togo’s private position was more nuanced than Suzuki’s; he told Sato that “we are adopting a policy of careful study.” That Stalin had not signed the declaration (Truman and Churchill did not ask him to) led to questions about the Soviet attitude. Togo asked Sato to try to meet with Soviet Foreign Minister Molotov as soon as possible to “sound out the Russian attitude” on the declaration as well as Japan’s end-the-war initiative. Sato cabled Togo earlier that he saw no point in approaching the Soviets on ending the war until Tokyo had “concrete proposals.” “Any aid from the Soviets has now become extremely doubtful.”

Document 54 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1222 – July 30, 1945, Top Secret Ultra

This report included an intercept of a message from Sato reporting that it was impossible to see Molotov and that unless the Togo had a “concrete and definite plan for terminating the war” he saw no point in attempting to meet with him.

Document 55 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1225 – August 2, 1945, Top Secret Ultra

An intercepted message from Togo to Sato showed that Tokyo remained interested in securing Moscow’s good office but that it “is difficult to decide on concrete peace conditions here at home all at once.” “[W]e are exerting ourselves to collect the views of all quarters on the matter of concrete terms.” Barton Bernstein, Richard Frank, and Tsuyoshi Hasegawa, among others, have argued that the “Magic” intercepts from the end of July and early August show that the Japanese were far from ready to surrender. According to Herbert Bix, for months Hirohito had believed that the “outlook for a negotiated peace could be improved if Japan fought and won one last decisive battle,” thus, he delayed surrender, continuing to “procrastinate until the bomb was dropped and the Soviets attacked.” [52]

Document 56 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1226 - August 3, 1945, Top Secret Ultra

This summary included intercepts of Japanese diplomatic reporting on the Soviet buildup in the Far East as well as a naval intelligence report on Anglo-American discussions of U.S. plans for the invasion of Japan. Part II of the summary includes the rest of Togo’s 2 August cable which instructed Sato to do what he could to arrange an interview with Molotov.

Document 57 : Walter Brown Meeting Notes, August 3, 1945

Historians have used this item in the papers of Byrne’s aide, Walter Brown, to make a variety of points. Richard Frank sees this brief discussion of Japan’s interest in Soviet diplomatic assistance as crucial evidence that Admiral Leahy had been sharing “MAGIC” information with President Truman. He also points out that Truman and his colleagues had no idea what was behind Japanese peace moves, only that Suzuki had declared that he would “ignore” the Potsdam Declaration. Alperovitz, however, treats it as additional evidence that “strongly suggests” that Truman saw alternatives to using the bomb. [53]

Document 58 : “Magic” – Far East Summary, War Department, Office of Assistant Chief of Staff, G-2, no. 502, 4 August 1945

Source: RG 457, Summaries of Intercepted Japanese Messages (“Magic” Far East Summary, March 20, 1942 – October 2, 1945), box 7, SRS 491-547

This “Far East Summary” included reports on the Japanese Army’s plans to disperse fuel stocks to reduce vulnerability to bombing attacks, the text of a directive by the commander of naval forces on “Operation Homeland,” the preparations and planning to repel a U.S. invasion of Honshu, and the specific identification of army divisions located in, or moving into, Kyushu. Both Richard Frank and Barton Bernstein have used intelligence reporting and analysis of the major buildup of Japanese forces on southern Kyushu to argue that U.S. military planners were so concerned about this development that by early August 1945 they were reconsidering their invasion plans. [54]

Document 59 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1228 – August 5, 1945, Top Secret Ultra

This summary included several intercepted messages from Sato, who conveyed his despair and exasperation over what he saw as Tokyo’s inability to develop terms for ending the war: “[I]f the Government and the Military dilly-dally in bringing this resolution to fruition, then all Japan will be reduced to ashes.” Sato remained skeptical that the Soviets would have any interest in discussions with Tokyo: “it is absolutely unthinkable that Russia would ignore the Three Power Proclamation and then engage in conversations with our special envoy.”

VIII. The Execution Order

Documents 60a-d: Framing the Directive for Nuclear Strikes:

60A . Cable VICTORY 213 from Marshall to Handy, July 22, 1945, Top Secret

60B . Memorandum from Colonel John Stone to General Arnold, “Groves Project,” 24 July 1945, Top Secret

60C . Cable WAR 37683 from General Handy to General Marshal, enclosing directive to General Spatz, July 24, 1945, Top Secret

60D . Cable VICTORY 261 from Marshall to General Handy, July 25, 1945, 25 July 1945, Top Secret

60E . General Thomas T. Handy to General Carl Spaatz, July 26, 1945, Top Secret

Source: RG 77, MED Records, Top Secret Documents, Files no. 5b and 5e ((copies from microfilm)

Top Army Air Force commanders may not have wanted to take responsibility for the first use of nuclear weapons on urban targets and sought formal authorization from Chief of Staff Marshall who was then in Potsdam. [55]  On 22 July Marshall asked Deputy Chief of Staff Thomas Handy to prepare a draft; General Groves wrote one which went to Potsdam for Marshall’s approval. Colonel John Stone, an assistant to commanding General of the Army Air Forces Henry H. “Hap” Arnold, had just returned from Potsdam and updated his boss on the plans as they had developed. On 25 July Marshall informed Handy that Secretary of War Stimson had approved the text; that same day, Handy signed off on a directive which ordered the use of atomic weapons on Japan, with the first weapon assigned to one of four possible targets—Hiroshima, Kokura, Niigata, or Nagasaki. “Additional bombs will be delivery on the [targets] as soon as made ready by the project staff.”

Document 61 : Memorandum from Major General L. R. Groves to Chief of Staff, July 30, 1945, Top Secret, Sanitized Copy

Source: RG 77, MED Records, Top Secret Documents, File no. 5

With more information on the Alamogordo test available, Groves provided Marshall with detail on the destructive power of atomic weapons. Barton J. Bernstein has observed that Groves’ recommendation that troops could move into the “immediate explosion area” within a half hour demonstrates the prevalent lack of top-level knowledge of the dangers of nuclear weapons effects. [56]  Groves also provided the schedule for the delivery of the weapons: the components of the gun-type bomb to be used on Hiroshima had arrived on Tinian, while the parts of the second weapon to be dropped were leaving San Francisco. By the end of November over ten weapons would be available, presumably in the event the war had continued.

Documents 62A-C: Weather delays

62A . CG 313 th  Bomb Wing, Tinian cable APCOM 5112 to War Department, August 3, 1945, Top Secret

62B . CG 313 th  Bomb Wing, Tinian cable APCOM 5130 to War Department, August 4, 1945, Top Secret

62C . CG 313 th  Bomb Wing, Tinian cable APCOM 5155 to War Department, August 4, 1945, Top Secret

Source: RG 77, Tinian Files, April-December 1945, box 21 (copies courtesy of Barton Bernstein)

The Hiroshima “operation” was originally slated to begin in early August depending on local conditions. As these cables indicate, reports of unfavorable weather delayed the plan. The second cable on 4 August shows that the schedule advanced to late in the evening of 5 August. The handwritten transcriptions are on the original archival copies.

IX. The First Nuclear Strikes and their Impact

Document 63 : Memorandum from General L. R. Groves to the Chief of Staff, August 6, 1945, Top Secret

Source: RG 77, MED Records, Top Secret Documents, File no. 5b (copy from microfilm)

Two days after the bombing of Hiroshima, Groves provided Chief of Staff Marshall with a report which included messages from Captain William S. Parsons and others about the impact of the detonation which, through prompt radiation effects, fire storms, and blast effects, immediately killed at least 70,000, with many dying later from radiation sickness and other causes. [57]

How influential the atomic bombings of Hiroshima and later Nagasaki compared to the impact of the Soviet declaration of war were to the Japanese decision to surrender has been the subject of controversy among historians. Sadao Asada emphasizes the shock of the atomic bombs, while Herbert Bix has suggested that Hiroshima and the Soviet declaration of war made Hirohito and his court believe that failure to end the war could lead to the destruction of the imperial house. Frank and Hasegawa divide over the impact of the Soviet declaration of war, with Frank declaring that the Soviet intervention was “significant but not decisive” and Hasegawa arguing that the two atomic bombs “were not sufficient to change the direction of Japanese diplomacy. The Soviet invasion was.” [58]

Document 64 : Walter Brown Diary Entry, 6 August 1945

Source:  Clemson University Libraries, Special Collections, Clemson, SC; Mss 243, Walter J. Brown Papers, box 68, folder 13, “Transcript/Draft B

Returning from the Potsdam Conference, sailing on the  U.S.S. Augusta , Truman learned about the atomic bombing of Hiroshima and announced it twice, first to those in the wardroom (socializing/dining area for commissioned officers), and then to the sailors’ mess. Still unaware of radiation effects, Truman emphasized the explosive yield. Later, he met with Secretary of State Byrnes and they discussed the Manhattan Project’s secrecy and the huge expenditures. Truman, who had been chair of the Senate Special Committee to Investigate the National Defense Program, said that “only on the appeal of Secretary of War Stimson did he refrain and let the War Department continue with the experiment unmolested.”

Document 65 : Directive from the Supreme Command Headquarters to the Commander-in-Chief of the Soviet Forces in the Far East on the Start of Combat Operations, No. 11122, Signed by [Communist Party General Secretary Joseph] Stalin and [Chief of General Staff A.I.] Antonov, 7 August 1945 (translation by Anna Melyakova)

Source: V. A. Zolotarev, ed.,  Sovetsko-Iaponskaia Voina 1945 Goda: Istoriia Voenno-Politicheskogo Protivoborstva Dvukh Derzhav v 30–40e Gody ( Moscow: Terra, 1997 and 2000), Vol. 7 (1), 340-341.

To keep his pledge at Yalta to enter the war against Japan and to secure the territorial concessions promised at the conference (e.g., Soviet annexation of the Kuriles and southern Sakhalin and a Soviet naval base at Port Arthur, etc.) Stalin considered various dates to schedule an attack. By early August he decided that 9-10 August 1945 would be the best dates for striking Japanese forces in Manchuria. In light of Japan’s efforts to seek Soviet mediation, Stalin wanted to enter the war quickly lest Tokyo reach a compromise peace with the Americans and the British at Moscow’s expense. But on 7 August, Stalin changed the instructions: the attack was to begin the next day. According to David Holloway, “it seems likely that the atomic bombing of Hiroshima the day before that impelled [Stalin] to speed up Soviet entry into the war” and “secure the gains promised at Yalta.” [59]

Document 66 : Memorandum of Conversation, “Atomic Bomb,” August 7, 1945

Source: Library of Congress Manuscript Division, Papers of W. Averell Harriman, box 181, Chron File Aug 5-9, 1945.

The Soviets already knew about the U.S. atomic project from espionage sources in the United States and Britain so Molotov’s comment to Ambassador Harriman about the secrecy surrounding the U.S. atomic project can be taken with a grain of salt, although the Soviets were probably unaware of specific plans for nuclear use.

Documents 67A-B:  Early High-level Reactions to the Hiroshima Bombing

67A : Cabinet Meeting and Togo's Meeting with the Emperor, August 7-8, 1945 Source: Gaimusho (Ministry of Foreign Affairs) ed.  Shusen Shiroku  (The Historical Records of the End of the War), annotated by Jun Eto, volume 4, 57-60 [Excerpts] [Translation by Toshihiro Higuchi]

67B : Admiral Tagaki Diary Entry for Wednesday, August 8 , 1945

Source: Takashi Itoh, ed.,  Sokichi Takagi: Nikki to Joho  [Sokichi Takagi: Diary and Documents] (Tokyo, Japan: Misuzu-Shobo, 2000), 923-924 [Translation by Hikaru Tajima]

Excerpts from the Foreign Ministry's compilation about the end of the war show how news of the bombing reached Tokyo as well as how Foreign Minister's Togo initially reacted to reports about Hiroshima. When he learned of the atomic bombing from the Domei News Agency, Togo believed that it was time to give up and advised the cabinet that the atomic attack provided the occasion for Japan to surrender on the basis of the Potsdam Declaration. Togo could not persuade the cabinet, however, and the Army wanted to delay any decisions until it had learned what had happened to Hiroshima. When the Foreign Minister met with the Emperor, Hirohito agreed with him; he declared that the top priority was an early end to the war, although it would be acceptable to seek better surrender terms--probably U.S. acceptance of a figure-head emperor--if it did not interfere with that goal. In light of those instructions, Togo and Prime Minister Suzuki agreed that the Supreme War Council should meet the next day.  [59a]

An entry from Admiral Tagaki's diary for August 8 conveys more information on the mood in elite Japanese circles after Hiroshima, but before the Soviet declaration of war and the bombing of Nagasaki. Seeing the bombing of Hiroshima as a sign of a worsening situation at home, Tagaki worried about further deterioration. Nevertheless, his diary suggests that military hard-liners were very much in charge and that Prime Minister Suzuki was talking tough against surrender, by evoking last ditch moments in Japanese history and warning of the danger that subordinate commanders might not obey surrender orders. The last remark aggravated Navy Minister Yonai who saw it as irresponsible. That the Soviets had made no responses to Sato's request for a meeting was understood as a bad sign; Yonai realized that the government had to prepare for the possibility that Moscow might not help. One of the visitors mentioned at the beginning of the entry was Iwao Yamazaki who became Minister of the Interior in the next cabinet.

Document 68 : Navy Secretary James Forrestal to President Truman, August 8, 1945

General Douglas MacArthur had been slated as commander for military operations against Japan’s mainland, this letter to Truman from Forrestal shows that the latter believed that the matter was not settled. Richard Frank sees this as evidence of the uncertainty felt by senior officials about the situation in early August; Forrestal would not have been so “audacious” to take an action that could ignite a “political firestorm” if he “seriously thought the end of the war was near.”

Document 69 : Memorandum of Conversation, “Far Eastern War and General Situation,” August 8, 1945, Top Secret

Source: Library of Congress Manuscript Division, Papers of W. Averell Harriman, box 181, Chron File Aug 5-9, 1945

Shortly after the Soviets declared war on Japan, in line with commitments made at the Yalta and Potsdam conferences, Ambassador Harriman met with Stalin, with George Kennan keeping the U.S. record of the meeting. After Stalin reviewed in considerable detail, Soviet military gains in the Far East, they discussed the possible impact of the atomic bombing on Japan’s position (Nagasaki had not yet been attacked) and the dangers and difficulty of an atomic weapons program. According to Hasegawa, this was an important, even “startling,” conversation: it showed that Stalin “took the atomic bomb seriously”; moreover, he disclosed that the Soviets were working on their own atomic program. [60]

Document 70 : Entries for 8-9 August, Robert P. Meiklejohn Diary

Source: W.A. Harriman Papers, Library of Congress, box 211 , Robert Pickens Meiklejohn World War II Diary At London and Moscow March 10, 1941-February 14, 1946 , Volume II (Privately printed, 1980 [Printed from hand-written originals]) (Reproduced with permission)

Robert P. Meiklejohn, who worked as Ambassador W. A. Harriman’s administrative assistant at the U.S. Embassies in Moscow and London during and after World War II, kept a detailed diary of his experiences and observations. The entries for 8 and 9 August, prepared in light of the bombing of Hiroshima, include discussion of the British contribution to the Manhattan Project, Harriman (“his nibs’”) report on his meeting with Molotov about the Soviet declaration of war, and speculation about the impact of the bombing of Hiroshima on the Soviet decision. According to Meiklejohn, “None of us doubt that the atomic bomb speeded up the Soviets’ declaration of war.”

Document 71 : Memorandum of Conference with the President, August 8, 1945 at 10:45 AM

At their first meeting after the dropping of the bomb on Hiroshima, Stimson briefed Truman on the scale of the destruction, with Truman recognizing the “terrible responsibility” that was on his shoulders. Consistent with his earlier attempts, Stimson encouraged Truman to find ways to expedite Japan’s surrender by using “kindness and tact” and not treating them in the same way as the Germans. They also discussed postwar legislation on the atom and the pending Henry D. Smyth report on the scientific work underlying the Manhattan project and postwar domestic controls of the atom.

Documents 72A-C: The Attack on Nagasaki:

72A . Cable APCOM 5445 from General Farrell to O’Leary [Groves assistant], August 9, 1945, Top Secret

72B . COMGENAAF 8 cable CMDW 576 to COMGENUSASTAF, for General Farrell, August 9, 1945, Top secret

72C . COMGENAAF 20 Guam cable AIMCCR 5532 to COMGENUSASTAF Guam, August 10, 1945, Top Secret

Source: RG 77, Tinian Files, April-December 1945, box 20, Envelope G Tinian Files, Top Secret

The prime target for the second atomic attack was Kokura, which had a large army arsenal and ordnance works, but various problems ruled that city out; instead, the crew of the B-29 that carried “Fat Man” flew to an alternate target at Nagasaki. These cables are the earliest reports of the mission; the bombing of Nagasaki killed immediately at least 39,000 people, with more dying later. According to Frank, the “actual total of deaths due to the atomic bombs will never be known,” but the “huge number” ranges somewhere between 100,000 and 200,000 people. Barton J. Bernstein and Martin Sherwin have argued that if top Washington policymakers had kept tight control of the delivery of the bomb instead of delegating it to Groves the attack on Nagasaki could have been avoided. The combination of the first bomb and the Soviet declaration of war would have been enough to induce Tokyo’s surrender. By contrast, Maddox argues that Nagasaki was necessary so that Japanese “hardliners” could not “minimize the first explosion” or otherwise explain it away. [61]

Documents 73A-B: Ramsey Letter from Tinian Island

73A : Letter from Norman Ramsey to J. Robert Oppenheimer, undated [mid-August 1945], Secret, excerpts Source: Library of Congress, J. Robert Oppenheimer Papers, box 60, Ramsey, Norman

73B : Transcript of the letter prepared by editor.

Ramsey, a physicist, served as deputy director of the bomb delivery group, Project Alberta. This personal account, written on Tinian, reports his fears about the danger of a nuclear accident, the confusion surrounding the Nagasaki attack, and early Air Force thinking about a nuclear strike force.

X. Toward Surrender

Document 74 : “Magic” – Far East Summary, War Department, Office of Assistant Chief of Staff, G-2, no. 507, August 9, 1945

Within days after the bombing of Hiroshima, U.S. military intelligence intercepted Japanese reports on the destruction of the city. According to an “Eyewitness Account (and Estimates Heard) … In Regard to the Bombing of Hiroshima”: “Casualties have been estimated at 100,000 persons.”

Document 75 : “Hoshina Memorandum” on the Emperor’s “Sacred Decision [ go-seidan] ,” 9-10 August, 1945

Source: Zenshiro Hoshina,  Daitoa Senso Hishi: Hoshina Zenshiro Kaiso-roku  [Secret History of the Greater East Asia War: Memoir of Zenshiro Hoshina] (Tokyo, Japan: Hara-Shobo, 1975), excerpts from Section 5, “The Emperor made  go-seidan  [= the sacred decision] – the decision to terminate the war,” 139-149 [translation by Hikaru Tajima]

Despite the bombing of Hiroshima, the Soviet declaration of war, and growing worry about domestic instability, the Japanese cabinet (whose decisions required unanimity) could not form a consensus to accept the Potsdam Declaration. Members of the Supreme War Council—“the Big Six” [62] —wanted the reply to Potsdam to include at least four conditions (e.g., no occupation, voluntary disarmament); they were willing to fight to the finish. The peace party, however, deftly maneuvered to break the stalemate by persuading a reluctant emperor to intervene. According to Hasegawa, Hirohito had become convinced that the preservation of the monarchy was at stake. Late in the evening of 9 August, the emperor and his advisers met in the bomb shelter of the Imperial Palace.

Zenshiro Hoshina, a senior naval official, attended the conference and prepared a detailed account. With Prime Minister Suzuki presiding, each of the ministers had a chance to state their views directly to Hirohito. While Army Minister Anami tacitly threatened a coup (“civil war”), the emperor accepted the majority view that the reply to the Potsdam declaration should include only one condition not the four urged by “Big Six.” Nevertheless, the condition that Hirohito accepted was not the one that foreign minister Togo had brought to the conference. What was at stake was the definition of the  kokutai  (national policy). Togo’s proposal would have been generally consistent with a constitutional monarchy because it defined the  kokutai  narrowly as the emperor and the imperial household. What Hirohito accepted, however, was a proposal by the extreme nationalist Kiichiro Hiranuma which drew upon prevailing understandings of the  kokutai : the “mythical notion” that the emperor was a living god. “This was the affirmation of the emperor’s theocratic powers, unencumbered by any law, based on Shinto gods in antiquity, and totally incompatible with a constitutional monarchy.” Thus, the Japanese response to the Potsdam declaration opposed “any demand which prejudices the prerogatives of his Majesty as a sovereign ruler.” This proved to be unacceptable to the Truman administration. [63]

Document 76 :“Magic’ – Far East Summary, War Department, Office of Assistant Chief of Staff, G-2, no. 508, August 10, 1945

More intercepted messages on the bombing of Hiroshima.

Documents 77A-B: The First Japanese Offer Intercepted

77A . “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1233 – August 10, 1945, Top Secret Ultra

77B . Translation of intercepted Japanese messages, circa 10 August 10, 1945, Top Secret Ultra

The first Japanese surrender offer was intercepted shortly before Tokyo broadcast it. This issue of the diplomatic summary also includes Togo’s account of his notification of the Soviet declaration of war, reports of Soviet military operations in the Far East, and intercepts of French diplomatic traffic. A full translation of the surrender offer was circulated separately. The translations differ but they convey the sticking point that prevented U.S. acceptance: Tokyo’s condition that the allies not make any “demand which prejudices the prerogatives of His Majesty as a sovereign ruler.”

Document 78 : Diary Entry, Friday, August 10, 1945, Henry Wallace Diary

Source: Papers of Henry A. Wallace, Special Collections Department, University of Iowa Libraries, Iowa City, Iowa (copy courtesy of Special Collections Department)

Note: The second page of the diary entry includes a newspaper clipping of the Associated Press’s transmission of the Byrnes note. Unfortunately, AP would not authorize the Archive to reproduce this item without payment. Therefore, we are publishing an excised version of the entry, with a link to the  Byrnes note .

Secretary of Commerce (and former Vice President) Henry Wallace provided a detailed report on the cabinet meeting where Truman and his advisers discussed the Japanese surrender offer, Russian moves into Manchuria, and public opinion on “hard” surrender terms. With Japan close to capitulation, Truman asserted presidential control and ordered a halt to atomic bombings. Barton J. Bernstein has suggested that Truman’s comment about “all those kids” showed his belated recognition that the bomb caused mass casualties and that the target was not purely a military one. [64]

Document 79 : Entries for 10-11 August, Robert P. Meiklejohn Diary

In these entries, Meiklejohn discussed how he and others in the Moscow Embassy learned about the bombing of Nagasaki from the “OWI Bulletin.” Entries for 10 and 11 August cover discussion at the Embassy about the radio broadcast announcing that Japan would surrender as long the Emperor’s status was not affected. Harriman opined that “surrender is in the bag” because of the Potsdam Declaration’s provision that the Japanese could “choose their own form of government, which would probably include the Emperor.” Further, “the only alternative to the Emperor is Communism,” implying that an official role for the Emperor was necessary to preserve social stability and prevent social revolution.

Document 80 : Stimson Diary Entries, Friday and Saturday, August 10 and 11, 1945

Stimson’s account of the events of 10 August focused on the debate over the reply to the Japanese note, especially the question of the Emperor’s status.  The U.S. reply , drafted during the course of the day, did not explicitly reject the note but suggested that any notion about the “prerogatives” of the Emperor would be superceded by the concept that all Japanese would be “Subject to the Supreme Commander of the Allied Powers.” The language was ambiguous enough to enable Japanese readers, upon Hirohito’s urging, to believe that they could decide for themselves the Emperor’s future role. Stimson accepted the language believing that a speedy reply to the Japanese would allow the United States to “get the homeland into our hands before the Russians could put in any substantial claim to occupy and help rule it.” If the note had included specific provision for a constitutional monarchy, Hasegawa argues, it would have “taken the wind out of the sails” of the military faction and Japan might have surrendered several days earlier, on August 11 or 12 instead of August 14. [65]

Document 81 : Entries from Walter Brown Diary, 10-11 August 1945

Source:  Clemson University Libraries, Special Collections, Clemson, SC; Mss 243, Walter Brown Papers, box 68, folder 13, “Transcript/Draft B

Brown recounted Byrnes’ debriefing of the 10 August White House meeting on the Japanese peace offer, an account which differed somewhat from that in the Stimson diary .  According to what Byrnes told Brown, Truman, Stimson, and Leahy favored accepting the Japanese note, but Byrnes objected that the United States should “go [no] further than we were willing to go at Potsdam.” Stimson’s account of the meeting noted Byrnes’ concerns (“troubled and anxious”) about the Japanese note and implied that he (Stimson) favored accepting it, but did not picture the debate as starkly as Browns's did.

Document 82 : General L. R. Groves to Chief of Staff George C. Marshall,  August 10, 1945, Top Secret, with a hand-written note by General Marshall

Source: George C. Marshall Papers, George C. Marshall Library, Lexington, VA (copy courtesy of Barton J. Bernstein)

Groves informed General Marshall that he was making plans for the use of a third atomic weapon sometime after 17 August, depending on the weather. With Truman having ordered a halt to the atomic bombings [See document 78], Marshall wrote on Grove's memo that the bomb was “not to be released over Japan without express authority from the President.”

Document 83 : Memorandum of Conversation, “Japanese Surrender Negotiations,” August 10, 1945, Top Secret

Source: Library of Congress Manuscript Division, Papers of W. Averell Harriman, box 181, Chron File Aug 10-12, 1945

Japan’s prospective surrender was the subject of detailed discussion between Harriman, British Ambassador Kerr, and Soviet Foreign Minister Molotov during the evening of August 10 (with a follow-up meeting occurring at 2 a.m.). In the course of the conversation, Harriman received a message from Washington that included the proposed U.S. reply and a request for Soviet support of the reply. After considerable pressure from Harriman, the Soviets signed off on the reply but not before tensions surfaced over the control of Japan--whether Moscow would have a Supreme Commander there as well. This marked the beginning of a U.S.-Soviet “tug of war” over occupation arrangements for Japan. [66]

Document 84 : Admiral Tagaki Diary Entry for 12 August [1945] Source: Takashi Itoh, ed.,  Sokichi Takagi: Nikki to Joho  [Sokichi Takagi: Diary and Documents] (Tokyo, Japan: Misuzu-Shobo, 2000), 926-927 [Translation by Hikaru Tajima]

As various factions in the government maneuvered on how to respond to the Byrnes note, Navy Minister Yonai and Admiral Tagaki discussed the latest developments. Yonai was upset that Chief of Staff Yoshijiro Umezu and naval chief Suemu Toyada had sent the emperor a memorandum arguing that acceptance of the Brynes note would “desecrate the emperor’s dignity” and turn Japan into virtually a “slave nation.” The emperor chided Umezu and Toyoda for drawing hasty conclusions; in this he had the support of Yonai, who also dressed them down. As Yonai explained to Tagaki, he had also confronted naval vice Chief Takijiro Onishi to make sure that he obeyed any decision by the Emperor. Yonai made sure that Takagi understood his reasons for bringing the war to an end and why he believed that the atomic bomb and the Soviet declaration of war had made it easier for Japan to surrender. [67]

Document 85 : Memorandum from Major General Clayton Bissell, Assistant Chief of Staff, G-2, for the Chief of Staff, “Estimate of Japanese Situation for Next 30 Days,” August 12, 1945, Top Secret

Source: National Archives, RG 165, Army Operations OPD, Executive Files 1940-1945, box 12, Exec #2

Not altogether certain that surrender was imminent, Army intelligence did not rule out the possibility that Tokyo would try to “drag out the negotiations” or reject the Byrnes proposal and continue fighting. If the Japanese decided to keep fighting, G-2 opined that “Atomic bombs will not have a decisive effect in the next 30 days.” Richard Frank has pointed out that this and other documents indicate that high level military figures remained unsure as to how close Japan really was to surrender.

Document 86 : The Cabinet Meeting over the Reply to the Four Powers (August 13)

Source:  Gaimusho [Ministry of Foreign Affairs], ed., Shusen Shiroku [Historical Record of the End of the War] (Tokyo: Hokuyosha, 1977-1978), vol. 5, 27-35 [Translated by Toshihiro Higuchi]

The Byrnes Note did not break the stalemate at the cabinet level. An account of the cabinet debates on August 13 prepared by Information Minister Toshiro Shimamura showed the same divisions as before; Anami and a few other ministers continued to argue that the Allies threatened the  kokutai  and that setting the four conditions (no occupation, etc.) did not mean that the war would continue. Nevertheless, Anami argued, “We are still left with some power to fight.” Suzuki, who was working quietly with the peace party, declared that the Allied terms were acceptable because they gave a “dim hope in the dark” of preserving the emperor. At the end of the meeting, he announced that he would report to Hirohito and ask him to make another “Sacred Judgment”. Meanwhile, junior Army officers plotted a coup to thwart the plans for surrender. [68]

Document 87 : Telephone conversation transcript, General Hull and Colonel Seaman [sic] – 1325 – 13 Aug 45, Top Secret

Source: George C. Marshall Library, Lexington, VA, George C. Marshall Papers (copy courtesy of Barton J. Bernstein)

While Truman had rescinded the order to drop nuclear bombs, the war was not yet over and uncertainty about Japan’s next step motivated war planner General John E. Hull (assistant chief of staff for the War Department’s Operations Division), and one of Groves’ associates, Colonel L. E. Seeman, to continue thinking about further nuclear use and its relationship to a possible invasion of Japan. As Hull explained, “should we not concentrate on targets that will be of greatest assistance to an invasion rather than industry, morale, psychology, etc.” “Nearer the tactical use”, Seaman agreed and they discussed the tactics that could be used for beach landings. In 1991 articles, Barton Bernstein and Marc Gallicchio used this and other evidence to develop the argument that concepts of tactical nuclear weapons use first came to light at the close of World War II. [69]

Document 88 : “Magic” – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1236 – August 13, 1945, Top Secret Ultra

The dropping of two atomic bombs, the tremendous destruction caused by U.S. bombing, and the Soviet declaration of war notwithstanding, important elements of the Japanese Army were unwilling to yield, as was evident from intercepted messages dated 12 and 13 August. Willingness to accept even the “destruction of the Army and Navy” rather than surrender inspired the military coup that unfolded and failed during the night of 14 August.

Document 89 : “The Second  Sacred Judgment”, August 14, 1945

Source :   Hiroshi [Kaian) Shimomura, S husenki [Account of the End of the War]  (Tokyo, Kamakura Bunko, [1948], 148-152 [Translated by Toshihiro Higuchi]

Frightened by the rapid movement of Soviet forces into Manchuria and worried that the army might launch a coup, the peace party set in motion a plan to persuade Hirohito to meet with the cabinet and the “Big Six” to resolve the stalemate over the response to the Allies. Japan was already a day late in responding to the Byrnes Note and Hirohito agreed to move quickly. At 10:50 a.m., he met with the leadership at the bomb shelter in his palace. This account, prepared by Director of Information Shimomura, conveys the drama of the occasion (as well as his interest in shifting the blame for the debacle to the Army). After Suzuki gave the war party--Umeda, Toyoda, and Anami--an opportunity to present their arguments against accepting the Byrnes Note, he asked the emperor to speak. 

  Hirohito asked the leadership to accept the Note, which he believed was “well intentioned” on the matter of the “national polity” (by leaving open a possible role for the Emperor).  Arguing that continuing the war would reduce the nation “to ashes,” his words about “bearing the unbearable” and sadness over wartime losses and suffering prefigured the language that Hirohito would use in his public announcement the next day. According to Bix, “Hirohito's language helped to transform him from a war to a peace leader, from a cold, aloof monarch to a human being who cared for his people” but “what chiefly motivated him … was his desire to save a politically empowered throne with himself on it.” [70]

Hirohito said that he would make a recording of the surrender announcement so that the nation could hear it. That evening army officers tried to seize the palace and find Hirohito’s recording, but the coup failed. Early the next day, General Anami committed suicide. On the morning of August 15, Hirohito broadcast the message to the nation (although he never used the word “surrender”). A few weeks later, on September 2, 1945 Japanese representatives signed surrender documents on the USS  Missouri , in Tokyo harbor. [71]

Document 90 : “Magic” – Far East Summary, War Department, Office of Assistant Chief of Staff, G-2, no. 515, August 18, 1945

This summary includes an intercepted account of the destruction of Nagasaki.

Document 91 :Washington Embassy Telegram 5599 to Foreign Office, 14 August 1945, Top Secret [72]

Source: The British National Archives, Records of the Foreign and Commonwealth Office,  FO 800/461

With the Japanese surrender announcement not yet in, President Truman believed that another atomic bombing might become necessary. After a White House meeting on 14 August, British Minister John Balfour reported that Truman had “remarked sadly that he now had no alternative but to order an atomic bomb to be dropped on Tokyo.” This was likely emotional thinking spurred by anxiety and uncertainty. Truman was apparently not considering the fact that Tokyo was already devastated by fire bombing and that an atomic bombing would have killed the Emperor, which would have greatly complicated the process of surrender. Moreover, he may not have known that the third bomb was still in the United States and would not be available for use for nearly another week. [73]  As it turned out, a few hours later, at 4:05 p.m., the White House received the Japanese surrender announcement.

XI. Confronting the Problem of Radiation Poisoning

Document 92 : P.L. Henshaw and R.R. Coveyou to H.J. Curtis and K. Z. Morgan, “Death from Radiation Burns,” 24 August 1945, Confidential

Source: Department of Energy Open-Net

Two scientists at Oak Ridge’s Health Division, Henshaw and Coveyou, saw a United Press report in the Knoxville  News Sentinel  about radiation sickness caused by the bombings. Victims who looked healthy weakened, “for unknown reasons” and many died. Lacking direct knowledge of conditions in Hiroshima and Nagasaki, Henshaw and Coveyou had their own data on the biological effects of radiation and could make educated guesses. After reviewing the impact of various atomic bomb effects--blast, heat, flash radiation (prompt effects from gamma waves), and radiation from radioactive substances--they concluded that “it seems highly plausible that a great many persons were subjected to lethal and sub-lethal dosages of radiation in areas where direct blast effects were possibly non-lethal.” It was “probable,” therefore, that radiation “would produce increments to the death rate and “even more probable” that a “great number of cases of sub-lethal exposures to radiation have been suffered.” [74]

Document 93 : Memorandum of Telephone Conversation Between General Groves and Lt. Col. Rea, Oak Ridge Hospital, 9:00 a.m., August 28, 1945, Top Secret

Source: RG 77, MED Records, Top Secret Documents, File no. 5b

Despite the reports pouring in from Japan about radiation sickness among the victims of Hiroshima and Nagasaki, General Groves and Dr. Charles Rea, a surgeon who was head of the base hospital at Oak Ridge (and had no specialized knowledge about the biological effects of radiation) dismissed the reports as “propaganda”. Unaware of the findings of Health Division scientists, Groves and Rhea saw the injuries as nothing more than “good thermal burns.” [75]

Documents 94A-B: General Farrell Surveys the Destruction

94A . Cable CAX 51813 from  USS Teton  to Commander in Chief Army Forces Pacific Administration, From Farrell to Groves, September 10, 1945, Secret

94B . Cable CAX 51948 from Commander in Chief Army Forces Pacific Advance Yokohoma Japan to Commander in Chief Army Forces Pacific Administration, September 14, 1945, Secret

Source: RG 77, Tinian Files, April-December 1945, box 17, Envelope B

A month after the attacks Groves’ deputy, General Farrell, traveled to Japan to see for himself the destruction of Hiroshima and Nagasaki. His vivid account shows that senior military officials in the Manhattan Project were no longer dismissive of reports of radiation poisoning. As Farrell observed in his discussion of Hiroshima, “Summaries of Japanese reports previously sent are essentially correct, as to clinical effects from single gamma radiation dose.” Such findings dismayed Groves, who worried that the bomb would fall into a taboo category like chemical weapons, with all the fear and horror surrounding them. Thus, Groves and others would try to suppress findings about radioactive effects, although that was a losing proposition. [76]

XII. Eisenhower and McCloy’s Views on the Bombings and Atomic Weapons

Document 95 : Entry for 4 October 1945, Robert P. Meiklejohn Diary

In this entry written several months later, Meiklejohn shed light on what much later became an element of the controversy over the Hiroshima-Nagasaki bombings: whether any high level civilian or military officials objected to nuclear use. Meiklejohn recounted Harriman’s visit in early October 1945 to the Frankfurt-area residence of General Dwight Eisenhower, who was finishing up his service as Commanding General, U.S. Army, European Theater. It was Meiklejohn’s birthday and during the dinner party, Eisenhower and McCloy had an interesting discussion of atomic weapons, which included comments alluding to scientists’ statements about what appears to be the H-bomb project (a 20 megaton weapon), recollection of the early fear that an atomic detonation could burn up the atmosphere, and the Navy’s reluctance to use its battleships to test atomic weapons. At the beginning of the discussion, Eisenhower made a significant statement: he “mentioned how he had hoped that the war might have ended without our having to use the atomic bomb.” The general implication was that prior to Hiroshima-Nagasaki, he had wanted to avoid using the bomb.

Some may associate this statement with one that Eisenhower later recalled making to Stimson. In his 1948 memoirs (further amplified in his 1963 memoirs), Eisenhower claimed that he had “expressed the hope [to Stimson] that we would never have to use such a thing against an enemy because I disliked seeing the United States take the lead in introducing into war something as horrible and destructive as this new weapon was described to be.” That language may reflect the underlying thinking behind Eisenhower’s statement during the dinner party, but whether Eisenhower used such language when speaking with Stimson has been a matter of controversy. In later years, those who knew both thought it unlikely that the general would have expressed misgivings about using the bomb to a civilian superior. Eisenhower’s son John cast doubts about the memoir statements, although he attested that when the general first learned about the bomb he was downcast.

Stimson’s diary mentions meetings with Eisenhower twice in the weeks before Hiroshima, but without any mention of a dissenting Eisenhower statement (and Stimson’s diaries are quite detailed on atomic matters). The entry from Meiklejohn’s diary does not prove or disprove Eisenhower’s recollection, but it does confirm that he had doubts which he expressed only a few months after the bombings. Whether Eisenhower expressed such reservations prior to Hiroshima will remain a matter of controversy. [77]

Document 96:  President Harry S. Truman, Handwritten Remarks for Gridiron Dinner, circa 15 December 1945 [78]

Source: Harry S. Truman Library,  President's Secretary's Files,  Speech Files, 1945-1953,  copy on U.S. National Archives Web Site

On 15 December, President Truman spoke about the atomic bombings in his speech at the annual dinner of the Gridiron Club, organized by bureau chiefs and other leading figures of print media organizations. Besides Truman, guests included New York Governor Thomas Dewey (Republican presidential candidate in 1944 and 1948), foreign ambassadors, members of the cabinet and the Supreme Court, the military high command, and various senators and representatives. The U.S. Marine Band provided music for the dinner and for the variety show that was performed by members of the press.  [79]

In accordance with the dinner’s rules that “reporters are never present,” Truman’s remarks were off-the record. The president, however, wrote in long-hand a text that that might approximate what he said that evening. Pages 12 through 15 of those notes refer to the atomic bombing of Japan:

“You know the most terrible decision a man ever had to make was made by me at Potsdam. It had nothing to do with Russia or Britain or Germany. It was a decision to loose the most terrible of all destructive forces for the wholesale slaughter of human beings. The Secretary of War, Mr. Stimson, and I weighed that decision most prayerfully. But the President had to decide. It occurred to me that a quarter of a million of the flower of our young manhood was worth a couple of Japanese cities, and I still think that they were and are. But I couldn’t help but think of the necessity of blotting out women and children and non-combatants. We gave them fair warning and asked them to quit. We picked a couple of cities where war work was the principle industry, and dropped bombs. Russia hurried in and the war ended.”

Truman characterized the Potsdam Declaration as a “fair warning,” but it was an ultimatum. Plainly he was troubled by the devastation and suffering caused by the bombings, but he found it justifiable because it saved the lives of U.S. troops. His estimate of 250,000 U.S. soldiers spared far exceeded that made by General Marshall in June 1945, which was in the range of 31,000 (comparable to the Battle of Luzon) [See Document 26]. By citing an inflated casualty figure, the president was giving a trial run for the rationale that would become central to official and semi-official discourse about the bombings during the decades ahead. [80]  

Despite Truman’s claim that he made “the most terrible” decision at Potsdam, he assigned himself more responsibility than the historical record supports. On the basic decision, he had simply concurred with the judgments of Stimson, Groves, and others that the bomb would be used as soon as it was available for military use. As for targeting, however, he had a more significant role. At Potsdam, Stimson raised his objections to targeting Japan’s cultural capital, Kyoto, and Truman supported the secretary’s efforts to drop that city from the target list [See Documents 47 and 48].  [81]

Where he had taken significant responsibility was by making a decision to stop the atomic bombings just before the Japanese surrender, thereby asserting presidential control over nuclear weapons

The editor thanks Barton J. Bernstein, J. Samuel Walker, Gar Alperovitz, David Holloway, and Alex Wellerstein for their advice and assistance, and Tsuyoshi Hasegawa for kindly providing copies of some of the Japanese sources that were translated for this compilation. Hasegawa’s book,  Racing the Enemy: Stalin, Truman, and the Surrender of Japan  (Cambridge, Harvard University Press, 2005), includes invaluable information on Japanese sources. David Clark, an archivist at the Harry S. Truman Library, and James Cross, Manuscripts Archivist at Clemson University Library’s Special Collections, kindly provided material from their collections. The editor also thanks Kyle Hammond and Gregory Graves for research assistance and Toshihiro Higuchi and Hikaru Tajima (who then were graduate students in history at Georgetown University and the University of Tokyo respectively), for translating documents and answering questions on the Japanese sources. The editor thanks Anna Melyakova (National Security Archive) for translating Russian language material.

Read the documents

I. background on the u.s. atomic project   documents 1a-c: report of the uranium committee.

Document 1A

National Archives, Records of the Office of Scientific Research and Development, Record Group 227 (hereinafter RG 227), Bush-Conant papers microfilm collection, Roll 1, Target 2, Folder 1, "S-1 Historical File, Section A (1940-1941)."

Document 1B

See description of document 1A.

Document 1C

Document 2A

RG 227, Bush-Conant papers microfilm collection, Roll 1, Target 2, Folder 1, "S-1 Historical File, Section II (1941-1942)

Document 2B

Bush-Conant papers, S-1 Historical File, Reports to and Conferences with the President (1942-1944)

See description of document 2A.

National Archives, Record Group 77, Records of the Army Corps of Engineers (hereinafter RG 77), Manhattan Engineering District (MED), Minutes of the Military Policy Meeting (5 May 1943), Correspondence (“Top Secret”) of the Manhattan Engineer District, 1942-1946, microfilm publication M1109 (Washington, D.C.: National Archives and Records Administration, 1980), Roll 3, Target 6, Folder 23, “Military Policy Committee, Minutes of Meetings”

Before the Manhattan Project had produced any weapons, senior U.S. government officials had Japanese targets in mind. Besides discussing programmatic matters (e.g., status of gaseous diffusion plants, heavy water production for reactors, and staffing at Las Alamos), the participants agreed that the first use could be Japanese naval forces concentrated at Truk Harbor, an atoll in the Caroline Islands. If there was a misfire the weapon would be difficult for the Japanese to recover, which would not be the case if Tokyo was targeted. Targeting Germany was rejected because the Germans were considered more likely to “secure knowledge” from a defective weapon than the Japanese. That is, the United States could possibly be in danger if the Nazis acquired more knowledge about how to build a bomb. [9]

RG 77, Correspondence ("Top Secret") of the Manhattan Engineer District, 1942-1946, file 25M

This memorandum from General Groves to General Marshall captured how far the Manhattan Project had come in less than two years since Bush’s December 1942 report to President Roosevelt. Groves did not mention this but around the time he wrote this the Manhattan Project had working at its far-flung installations over 125,000 people ; taking into account high labor turnover some 485,000 people worked on the project (1 out of every 250 people in the country at that time). What these people were laboring to construct, directly or indirectly, were two types of weapons—a gun-type weapon using U-235 and an implosion weapon using plutonium (although the possibility of U-235 was also under consideration). As the scientists had learned, a gun-type weapon based on plutonium was “impossible” because that element had an “unexpected property”: spontaneous neutron emissions would cause the weapon to “fizzle.” [10] For both the gun-type and the implosion weapons, a production schedule had been established and both would be available during 1945. The discussion of weapons effects centered on blast damage models; radiation and other effects were overlooked.

RG 77, Harrison-Bundy Files (H-B Files), folder 69 (copy from microfilm)

Documents 6A-D: President Truman Learns the Secret

Document 6A

G 77, Commanding General’s file no. 24, tab D

Soon after he was sworn in as president following President Roosevelt’s death, Harry Truman learned about the top secret Manhattan Project from briefings by  Secretary of War Stimson and Manhattan Project chief General Groves (who went through the “back door” to escape the watchful press). Stimson, who later wrote up the meeting in his diary, also prepared a discussion paper, which raised broader policy issues associated with the imminent possession of “the most terrible weapon ever known in human history.”

In a background report prepared for the meeting, Groves provided a detailed overview of the bomb project from the raw materials to processing nuclear fuel to assembling the weapons to plans for using them, which were starting to crystallize. With respect to the point about assembling the weapons, Groves and Stimson informed Truman that the first gun-type weapon “should be ready about 1 August 1945” while an implosion weapon would also be available that month. “The target is and was always expected to be Japan.”  

These documents have important implications for the perennial debate over whether Truman “inherited assumptions” from the Roosevelt administration that the bomb would be used when available or that he made  the  decision to do so.  Alperovitz and Sherwin have argued that Truman made “a real decision” to use the bomb on Japan by choosing “between various forms of diplomacy and warfare.” In contrast, Bernstein found that Truman “never questioned [the] assumption” that the bomb would and should be used. Norris also noted that “Truman’s ”decision” amounted to a decision not to override previous plans to use the bomb.” [12]

Document 6B

Henry Stimson Diary, Sterling Library, Yale University (microfilm at Library of Congress)

See description of document 6A.

Document 6C

Record Group 200, Papers of General Leslie R. Groves, Correspondence 1941-1970, box 3, “F”

Document 6D

RG 77, MED Records, Top Secret Documents, File no. 5g

The force of B-29 nuclear delivery vehicles that was being readied for first nuclear use—the Army Air Force’s 509 th Composite Group—required an operational base in the Western Pacific. In late February 1945, months before atomic bombs were ready for use, the high command selected Tinian, an island in the Northern Marianas Islands, for that base.

Library of Congress, Curtis LeMay Papers, Box B-36

As part of the war with Japan, the Army Air Force waged a campaign to destroy major industrial centers with incendiary bombs. This document is General Curtis LeMay’s report on the firebombing of Tokyo--“the most destructive air raid in history”--which burned down over 16 square miles of the city, killed up to 100,000 civilians (the official figure was 83,793), injured more than 40,000, and made over 1 million homeless. [13] According to the “Foreword,” the purpose of the raid, which dropped 1,665 tons of incendiary bombs, was to destroy industrial and strategic targets “ not to bomb indiscriminately civilian populations.” Air Force planners, however, did not distinguish civilian workers from the industrial and strategic structures that they were trying to destroy.

RG 77, MED Records, Top Secret Documents, File no. 5d (copy from microfilm)

On 27 April, military officers and nuclear scientists met to discuss bombing techniques, criteria for target selection, and overall mission requirements. The discussion of “available targets” included Hiroshima, the “largest untouched target not on the 21 st Bomber Command priority list.” But other targets were under consideration, including Yawata (northern Kyushu), Yokohama, and Tokyo (even though it was practically “rubble.”) The problem was that the Air Force had a policy of “laying waste” to Japan’s cities which created tension with the objective of reserving some urban targets for nuclear destruction. [16]

Document 10

RG 77, MED Records, Top Secret Documents, File no. 5g (copy from microfilm)

As director of Los Alamos Laboratory, Oppenheimer’s priority was producing a deliverable bomb, but not so much the effects of the weapon on the people at the target. In keeping with General Groves’ emphasis on compartmentalization, the Manhattan Project experts on the effects of radiation on human biology were at the MetLab and other offices and had no interaction with the production and targeting units. In this short memorandum to Groves’ deputy, General Farrell, Oppenheimer explained the need for precautions because of the radiological dangers of a nuclear detonation. The initial radiation from the detonation would be fatal within a radius of about 6/10ths of a mile and “injurious” within a radius of a mile. The point was to keep the bombing mission crew safe; concern about radiation effects had no impact on targeting decisions. [17]

Document 11

Scientists and officers held further discussion of bombing mission requirements, including height of detonation, weather, radiation effects (Oppenheimer’s memo), plans for possible mission abort, and the various aspects of target selection, including priority cities (“a large urban area of more than three miles diameter”) and psychological dimension. As for target cities, the committee agreed that the following should be exempt from Army Air Force bombing so they would be available for nuclear targeting: Kyoto, Hiroshima, Yokohama, and Kokura Arsenal. Japan’s cultural capital, Kyoto, would not stay on the list. Pressure from Secretary of War Stimson had already taken Kyoto off the list of targets for incendiary bombings and he would successfully object to the atomic bombing of that city. [18]

Document 12

Document 13

Joseph E. Davies Papers, Library of Congress, box 17, 21 May 1945

Document 14

Harrison-Bundy Files relating to the Development of the Atomic Bomb, 1942-1946, microfilm publication M1108 (Washington, D.C.: National Archives and Records Administration, 1980), File 77: "Interim Committee - International Control."

In what Stimson called the “letter of an honest man,” Oswald C. Brewster sent President Truman a profound analysis of the danger and unfeasibility of a U.S. atomic monopoly. [21] An engineer for the Kellex Corporation, which was involved in the gas diffusion project to enrich uranium, Brewster recognized that the objective was fissile material for a weapon. That goal, he feared, raised terrifying prospects with implications for the “inevitable destruction of our present day civilization.” Once the U.S. had used the bomb in combat other great powers would not tolerate a monopoly by any nation and the sole possessor would be “be the most hated and feared nation on earth.” Even the U.S.’s closest allies would want the bomb because “how could they know where our friendship might be five, ten, or twenty years hence.” Nuclear proliferation and arms races would be certain unless the U.S. worked toward international supervision and inspection of nuclear plants.

Document 15

Document 16

At the end of May General Groves forwarded to Army Chief of Staff Marshall a “Plan of Operations” for the atomic bombings. While that plan has not surfaced, apparently its major features were incorporated in this 29 May 1945 message on the “special functions” of the 509th Composite Group sent from Chief of Staff General Lauris Norstad to General Curtis LeMay, chief of the XXI Bomber Command, headquartered in the Marianas Islands. [21A] The Norstad message reviewed the complex requirements for preparing B-29s and their crew for delivering nuclear weapons.  He detailed the mission of the specially modified B-29s that comprised the  509th Composite Group, the “tactical factors” that applied,  training and rehearsal issues, and the functions of “special personnel” and the Operational Studies Group.  The targets listed—Hiroshima, Kyoto, and Niigato—were those that had been discussed at the Target Committee meeting on 28 May, but Kyoto would be dropped when Secretary Stimson objected (although that would remain a contested matter) and Kokura would eventually be substituted.   As part of the Composite Group’s training to drop “special bombs,” it would practice with facsimiles—the conventionally-armed “Pumpkins.” The 509th Composite Group’s cover story for its secret mission was the preparation for the use of “Pumpkins” in battle.

Document 17

Record Group 107, Office of the Secretary of War, Formerly Top Secret Correspondence of Secretary of War Stimson (“Safe File”), July 1940-September 1945, box 12, S-1

Tacitly dissenting from the Targeting Committee’s recommendations, Army Chief of Staff George Marshall argued for initial nuclear use against a clear-cut military target such as a “large naval installation.” If that did not work, manufacturing areas could be targeted, but only after warning their inhabitants. Marshall noted the “opprobrium which might follow from an ill considered employment of such force.” This document has played a role in arguments developed by Barton J. Bernstein that figures such as Marshall and Stimson were “caught between an older morality that opposed the intentional killing of non-combatants and a newer one that stressed virtually total war.” [22]

Document 18

RG 77, MED Records, H-B files, folder no. 100 (copy from microfilm)

With Secretary of War Stimson presiding, members of the committee heard reports on a variety of Manhattan Project issues, including the stages of development of the atomic project,  problems of secrecy, the possibility of informing the Soviet Union, cooperation with “like-minded” powers, the military impact of the bomb on Japan, and the problem of “undesirable scientists.”  In his comments on a detonation over Japanese targets, Oppenheimer mentioned that the “neutron effect would be dangerous to life for a radius of at least two-thirds of a mile,” but did not mention that the radiation could cause prolonged sickness.

Interested in producing the “greatest psychological effect,” the Committee members agreed that the “most desirable target would be a vital war plant employing a large number of workers and closely surrounded by workers’ houses.”  Bernstein argues that this target choice represented an uneasy endorsement of “terror bombing”-the target was not exclusively military or civilian; nevertheless, worker’s housing would include non-combatant men, women, and children. [23] It is possible that Truman was informed of such discussions and their conclusions, although he clung to a belief that the prospective targets were strictly military.

Document 19

Record Group 165, Records of the War Department General and Special Staffs, American-British-Canadian Top Secret Correspondence, Box 504, “ABC 387 Japan (15 Feb. 45)

George A. Lincoln, chief of the Strategy and Policy Group at U.S. Army’s Operations Department, commented on a memorandum by former President Herbert Hoover that Stimson had passed on for analysis. Hoover proposed a compromise solution with Japan that would allow Tokyo to retain part of its empire in East Asia (including Korea and Japan) as a way to head off Soviet influence in the region. While Lincoln believed that the proposed peace teams were militarily acceptable he doubted that they were workable or that they could check Soviet “expansion” which he saw as an inescapable result of World War II. As to how the war with Japan would end, he saw it as “unpredictable,” but speculated that “it will take Russian entry into the war, combined with a landing, or imminent threat of a landing, on Japan proper by us, to convince them of the hopelessness of their situation.” Lincoln derided Hoover’s casualty estimate of 500,000. J. Samuel Walker has cited this document to make the point that “contrary to revisionist assertions, American policymakers in the summer of 1945 were far from certain that the Soviet invasion of Manchuria would be enough in itself to force a Japanese surrender.” [24]

Document 20

Document 21

Henry Stimson Papers, Sterling Library, Yale University (microfilm at Library of Congress)

Stimson and Truman began this meeting by discussing how they should handle a conflict with French President DeGaulle over the movement by French forces into Italian territory. (Truman finally cut off military aid to France to compel the French to pull back). [25] As evident from the discussion, Stimson strongly disliked de Gaulle whom he regarded as “psychopathic.” The conversation soon turned to the atomic bomb, with some discussion about plans to inform the Soviets but only after a successful test. Both agreed that the possibility of a nuclear “partnership” with Moscow would depend on “quid pro quos”: “the settlement of the Polish, Rumanian, Yugoslavian, and Manchurian problems.”

At the end, Stimson shared his doubts about targeting cities and killing civilians through area bombing because of its impact on the U.S.’s reputation as well as on the problem of finding targets for the atomic bomb. Barton Bernstein has also pointed to this as additional evidence of the influence on Stimson of an “an older morality.” While concerned about the U.S.’s reputation, Stimson did not want the Air Force to bomb Japanese cities so thoroughly that the “new weapon would not have a fair background to show its strength,” a comment that made Truman laugh. The discussion of “area bombing” may have reminded him that Japanese civilians remained at risk from U.S. bombing operations.

Document 22

RG 77, MED Records, H-B files, folder no. 76 (copy from microfilm)

Physicists Leo Szilard and James Franck, a Nobel Prize winner, were on the staff of the “Metallurgical Laboratory” at the University of Chicago, a cover for the Manhattan Project program to produce fuel for the bomb. The outspoken Szilard was not involved in operational work on the bomb and General Groves kept him under surveillance but Met Lab director Arthur Compton found Szilard useful to have around. Concerned with the long-run implications of the bomb, Franck chaired a committee, in which Szilard and Eugene Rabinowitch were major contributors, that produced a report rejecting a surprise attack on Japan and recommended instead a demonstration of the bomb on the “desert or a barren island.” Arguing that a nuclear arms race “will be on in earnest not later than the morning after our first demonstration of the existence of nuclear weapons,” the committee saw international control as the alternative. That possibility would be difficult if the United States made first military use of the weapon. Compton raised doubts about the recommendations but urged Stimson to study the report. Martin Sherwin has argued that the Franck committee shared an important assumption with Truman et al.--that an “atomic attack against Japan would `shock’ the Russians”--but drew entirely different conclusions about the import of such a shock. [26]

Document 23

Record Group 107, Office of the Secretary of War, Formerly Top Secret Correspondence of Secretary of War Stimson (“Safe File”), July 1940-September 1945, box 8, Japan (After December 7/41)

Document 24

Document 25

Document 26

Record Group 218, Records of the Joint Chiefs of Staff, Central Decimal Files, 1942-1945, box 198 334 JCS (2-2-45) Mtg 186th-194th

The record of this meeting has figured in the complex debate over the estimates of casualties stemming from a possible invasion of Japan. While post-war justifications for the bomb suggested that an invasion of Japan could have produced very high levels of casualties (dead, wounded, or missing), from hundreds of thousands to a million, historians have vigorously debated the extent to which the estimates were inflated. [29]

Document 27

Document 28

RG 77, MED, H-B files, folder no. 77 (copy from microfilm)

Document 29

Document 30

RG 107, Office of Assistant Secretary of War Formerly Classified Correspondence of John J. McCloy, 1941-1945, box 38, ASW 387 Japan

Document 31

Document 32

Document 33

Naval Aide to the President Files, box 4, Berlin Conference File, Volume XI - Miscellaneous papers: Japan, Harry S. Truman Presidential Library

On 2 July Stimson presented to President Truman a proposal that he had worked up with colleagues in the War Department, including McCloy, Marshall, and Grew. The proposal has been characterized as “the most comprehensive attempt by any American policymaker to leverage diplomacy” in order to shorten the Pacific War. Stimson had in mind a “carefully timed warning” delivered before the invasion of Japan. Some of the key elements of Stimson’s argument were his assumption that “Japan is susceptible to reason” and that Japanese might be even more inclined to surrender if “we do not exclude a constitutional monarchy under her present dynasty.” The possibility of a Soviet attack would be part of the “threat.” As part of the threat message, Stimson alluded to the “inevitability and completeness of the destruction” which Japan could suffer, but he did not make it clear whether unconditional surrender terms should be clarified before using the atomic bomb. Truman read Stimson’s proposal, which he said was “powerful,” but made no commitments to the details, e.g., the position of the emperor. [32]

Document 34

Record Group 353, Records of Interdepartmental and Intradepartmental Committees, Secretary’s Staff Meetings Minutes, 1944-1947 (copy from microfilm)

Document 35

RG 218, Central Decimal Files, 1943-1945, CCS 381 (6-4-45), Sec. 2 Pt. 5

Document 36

Record Group 59, Decimal Files 1945-1949, 740.0011 PW (PE)/7-1645

Document 37

Henry L. Stimson Papers (MS 465), Sterling Library, Yale University (reel 113) (microfilm at Library of Congress)

Still interested in trying to find ways to “warn Japan into surrender,” this represents an attempt by Stimson before the Potsdam conference, to persuade Truman and Byrnes to agree to issue warnings to Japan prior to the use of the bomb. The warning would draw on the draft State-War proclamation to Japan; presumably, the one criticized by Hull (above) which included language about the emperor. Presumably the clarified warning would be issued prior to the use of the bomb; if the Japanese persisted in fighting then “the full force of our new weapons should be brought to bear” and a “heavier” warning would be issued backed by the “actual entrance of the Russians in the war.” Possibly, as Malloy has argued, Stimson was motivated by concerns about using the bomb against civilians and cities, but his latest proposal would meet resistance at Potsdam from Byrnes and other. [34]

Document 38

IV. The Japanese Search for Soviet Mediation   Documents 39A-B: Magic

Document 39A

National Security Agency Mandatory declassification review release.

Beginning in September 1940, U.S. military intelligence began to decrypt routinely, under the “Purple” code-name, the intercepted cable traffic of the Japanese Foreign Ministry. Collectively the decoded messages were known as “Magic.” How this came about is explained in an internal history of pre-war and World War II Army and Navy code-breaking activities prepared by William F. Friedman , a central figure in the development of U.S. government cryptology during the 20 th century. The National Security Agency kept the ‘Magic” diplomatic and military summaries classified for many years and did not release the entire series for 1942 through August 1945 until the early 1990s. [36]

Document 39B

Record Group 457, Records of the National Security Agency/Central Security Service, “Magic” Diplomatic Summaries 1942-1945, box 18.

Document 40

RG 165, Army Operations OPD Executive File #17, Item 13 (copy courtesy of J. Samuel Walker)

Document 41

Record Group 457, Records of the National Security Agency/Central Security Service, “Magic” Diplomatic Summaries 1942-1945, box 18

Document 42

Document 43

Takashi Itoh, ed., Sokichi Takagi: Nikki to Joho [Sokichi Takagi: Diary and Documents] (Tokyo, Japan: Misuzu-Shobo, 2000), 916-917 [Translation by Hikaru Tajima]

Document 44

L.D. Riabev, ed., Atomnyi Proekt SSSR (Moscow: izd MFTI, 2002), Volume 1, Part 2, 335-336

This 10 July 1945 letter from NKVD director V. N. Merkulov to Beria is an example of Soviet efforts to collect inside information on the Manhattan Project, although not all the detail was accurate. Merkulov reported that the United States had scheduled the test of a nuclear device for that same day, although the actual test took place 6 days later. According to Merkulov, two fissile materials were being produced: element-49 (plutonium), and U-235; the test device was fueled by plutonium. The Soviet source reported that the weight of the device was 3 tons (which was in the ball park) and forecast an explosive yield of 5 kilotons. That figure was based on underestimates by Manhattan Project scientists: the actual yield of the test device was 20 kilotons.

Document 45

RG 77, MED Records, Top Secret Documents, File 5e (copy from microfilm)

An elated message from Harrison to Stimson reported the success of the Trinity Test of a plutonium implosion weapon. The light from the explosion could been seen “from here [Washington, D.C.] to “high hold” [Stimson’s estate on Long Island—250 miles away]” and it was so loud that Harrison could have heard the “screams” from Washington, D.C. to “my farm” [in Upperville, VA, 50 miles away] [42]

Document 46

RG 77, MED Records, Top Secret Documents, File no. 4 (copy from microfilm)

Document 47

Barton J. Bernstein, “Truman at Potsdam: His Secret Diary,” Foreign Service Journal, July/August 1980, excerpts, used with author’s permission. [44]

Some years after Truman’s death, a hand-written diary that he kept during the Potsdam conference surfaced in his personal papers. For convenience, Barton Bernstein’s rendition is provided here but linked here are the scanned versions of Truman’s handwriting on the National Archives’ website (for 15-30 July).

Document 48

An important question that Stimson discussed with Marshall, at Truman’s request, was whether Soviet entry into the war remained necessary to secure Tokyo’s surrender. Marshall was not sure whether that was so although Stimson privately believed that the atomic bomb would provide enough to force surrender (see entry for July 23). This entry has been cited by all sides of the controversy over whether Truman was trying to keep the Soviets out of the war. [46] During the meeting on August 24, discussed above, Stimson gave his reasons for taking Kyoto off the atomic target list: destroying that city would have caused such “bitterness” that it could have become impossible “to reconcile the Japanese to us in that area rather than to the Russians.” Stimson vainly tried to preserve language in the Potsdam Declaration designed to assure the Japanese about “the continuance of their dynasty” but received Truman’s assurance that such a consideration could be conveyed later through diplomatic channels (see entry for July 24). Hasegawa argues that Truman realized that the Japanese would refuse a demand for unconditional surrender without a proviso on a constitutional monarchy and that “he needed Japan’s refusal to justify the use of the atomic bomb.” [47]

Document 49

Clemson University Libraries, Special Collections, Clemson, SC; Mss 243, Walter J. Brown Papers, box 10, folder 12, Byrnes, James F.: Potsdam, Minutes, July-August 1945

The degree to which the typed-up version reflects the original is worth investigating. In any event, historians have used information from the diary to support various interpretations. For example, Bernstein cites the entries for 20 and 24 July to argue that “American leaders did not view Soviet entry as a substitute for the bomb” but that the latter “would be so powerful, and the Soviet presence in Manchuria so militarily significant, that there was no need for actual Soviet intervention in the war.” For Brown's diary entry of 3 August 9 1945 historians have developed conflicting interpretations (See discussion of document 57). [48]

Document 50

Document 51

Naval Historical Center, Operational Archives, James Forrestal Diaries

Secretary of the Navy James Forrestal was a regular recipient of “Magic” intercept reports; this substantial entry reviews the dramatic Sato-Togo exchanges covered in the 22 July “Magic” summary (although Forrestal misdated Sato’s cable as “first of July” instead of the 21 st ). In contrast to Alperovitz’s argument that Forrestal tried to modify the terms of unconditional surrender to give the Japanese an out, Frank sees Forrestal’s account of the Sato-Togo exchange as additional evidence that senior U.S. officials understood that Tokyo was not on the “cusp of surrender.” [49]

Document 52

Joseph E. Davies Papers, Library of Congress, Manuscripts Division, box 19, 29 July 1945

VII. Debates among the Japanese – Late July/Early August 1945

Document 53

In the Potsdam Declaration the governments of China, Great Britain, and the United States) demanded the “unconditional surrender of all Japanese armed forces. “The alternative is prompt and utter destruction.” The next day, in response to questions from journalists about the government’s reaction to the ultimatum, Prime Minister Suzuki apparently said that “We can only ignore [ mokusatsu ] it. We will do our utmost to complete the war to the bitter end.” That, Bix argues, represents a “missed opportunity” to end the war and spare the Japanese from continued U.S. aerial attacks. [51] Togo’s private position was more nuanced than Suzuki’s; he told Sato that “we are adopting a policy of careful study.” That Stalin had not signed the declaration (Truman and Churchill did not ask him to) led to questions about the Soviet attitude. Togo asked Sato to try to meet with Soviet Foreign Minister Molotov as soon as possible to “sound out the Russian attitude” on the declaration as well as Japan’s end-the-war initiative. Sato cabled Togo earlier that he saw no point in approaching the Soviets on ending the war until Tokyo had “concrete proposals.” “Any aid from the Soviets has now become extremely doubtful.”

Document 54

Document 55

Document 56

Document 57

Document 58

RG 457, Summaries of Intercepted Japanese Messages (“Magic” Far East Summary, March 20, 1942 – October 2, 1945), box 7, SRS 491-547

Document 59

VIII. The Execution Order   Documents 60A-D: These messages convey the process of creating and transmitting the execution order to bomb Hiroshima. Possibly not wanting to take responsibility for the first use of nuclear weapons, Army Air Force commanders sought formal authorization from Chief of Staff Marshall who was then in Potsdam

Document 60A

RG 77, MED Records, Top Secret Documents, Files no. 5b and 5e (copies from microfilm)

These messages convey the process of creating and transmitting the execution order to bomb Hiroshima.  Possibly not wanting to take responsibility for the first use of nuclear weapons, Army Air Force commanders sought formal authorization from Chief of Staff Marshall who was then in Potsdam. [55] On 22 July Marshall asked Deputy Chief of Staff Thomas Handy to prepare a draft; General Groves wrote one which went to Potsdam for Marshall’s approval. Colonel John Stone, an assistant to commanding General of the Army Air Forces Henry H. “Hap” Arnold, had just returned from Potsdam and updated his boss on the plans as they had developed. On 25 July Marshall informed Handy that Secretary of War Stimson had approved the text; that same day, Handy signed off on a directive which ordered the use of atomic weapons on Japan, with the first weapon assigned to one of four possible targets—Hiroshima, Kokura, Niigata, or Nagasaki. “Additional bombs will be delivery on the [targets] as soon as made ready by the project staff.”

Document 60B

See description of document 60A.

Document 60C

Document 60D

Document 60E

Document 61

RG 77, MED Records, Top Secret Documents, File no. 5

With more information on the Alamogordo test available, Groves provided Marshall with detail on the destructive power of atomic weapons. Barton J. Bernstein has observed that Groves’ recommendation that troops could move into the “immediate explosion area” within a half hour demonstrates the prevalent lack of top-level knowledge of the dangers of nuclear weapons effects. [56] Groves also provided the schedule for the delivery of the weapons: the components of the gun-type bomb to be used on Hiroshima had arrived on Tinian, while the parts of the second weapon to be dropped were leaving San Francisco. By the end of November over ten weapons would be available, presumably in the event the war had continued.

Document 62A

RG 77, Tinian Files, April-December 1945, box 21 (copies courtesy of Barton Bernstein)

Document 62B

See description of document 62A.

Document 62C

Document 63

RG 77, MED Records, Top Secret Documents, File no. 5b (copy from microfilm)

Document 64

Clemson University Libraries, Special Collections, Clemson, SC; Mss 243, Walter J. Brown Papers, box 68, folder 13, “Transcript/Draft B

Returning from the Potsdam Conference, sailing on the U.S.S. Augusta , Truman learned about the atomic bombing of Hiroshima and announced it twice, first to those in the wardroom (socializing/dining area for commissioned officers), and then to the sailors’ mess. Still unaware of radiation effects, Truman emphasized the explosive yield. Later, he met with Secretary of State Byrnes and they discussed the Manhattan Project’s secrecy and the huge expenditures. Truman, who had been chair of the Senate Special Committee to Investigate the National Defense Program, said that “only on the appeal of Secretary of War Stimson did he refrain and let the War Department continue with the experiment unmolested.”

Document 65

A. Zolotarev, ed., Sovetsko-Iaponskaia Voina 1945 Goda: Istoriia Voenno-Politicheskogo Protivoborstva Dvukh Derzhav v 30–40e Gody (Moscow: Terra, 1997 and 2000), Vol. 7 (1), 340-341.

Document 66

Library of Congress Manuscript Division, Papers of W. Averell Harriman, box 181, Chron File Aug 5-9, 1945.

Documents 67A-B: Early High-level Reactions to the Hiroshima Bombing

Document 67A

Gaimusho (Ministry of Foreign Affairs) ed. Shusen Shiroku (The Historical Records of the End of the War), annotated by Jun Eto, volume 4, 57-60 [Excerpts] [Translation by Toshihiro Higuchi]

Excerpts from the Foreign Ministry's compilation about the end of the war show how news of the bombing reached Tokyo as well as how Foreign Minister's Togo initially reacted to reports about Hiroshima. When he learned of the atomic bombing from the Domei News Agency, Togo believed that it was time to give up and advised the cabinet that the atomic attack provided the occasion for Japan to surrender on the basis of the Potsdam Declaration. Togo could not persuade the cabinet, however, and the Army wanted to delay any decisions until it had learned what had happened to Hiroshima. When the Foreign Minister met with the Emperor, Hirohito agreed with him; he declared that the top priority was an early end to the war, although it would be acceptable to seek better surrender terms--probably U.S. acceptance of a figure-head emperor--if it did not interfere with that goal. In light of those instructions, Togo and Prime Minister Suzuki agreed that the Supreme War Council should meet the next day. [59a]

Document 67B

Takashi Itoh, ed., Sokichi Takagi: Nikki to Joho [Sokichi Takagi: Diary and Documents] (Tokyo, Japan: Misuzu-Shobo, 2000), 923-924 [Translation by Hikaru Tajima]

Document 68

Document 69

Library of Congress Manuscript Division, Papers of W. Averell Harriman, box 181, Chron File Aug 5-9, 1945

Document 70

W.A. Harriman Papers, Library of Congress, box 211, Robert Pickens Meiklejohn World War II Diary At London and Moscow March 10, 1941-February 14, 1946, Volume II (Privately printed, 1980 [Printed from hand-written originals]) (Reproduced with permission)

Document 71

Documents 72A-C: The Attack on Nagasaki

Document 72A

RG 77, Tinian Files, April-December 1945, box 20, Envelope G Tinian Files, Top Secret

Document 72B

See description of document 72A.

Document 72C

Document 73A

Library of Congress, J. Robert Oppenheimer Papers, box 60, Ramsey, Norman

Document 73B

See description of document 73A.

Document 74

Document 75

Zenshiro Hoshina, Daitoa Senso Hishi: Hoshina Zenshiro Kaiso-roku [Secret History of the Greater East Asia War: Memoir of Zenshiro Hoshina] (Tokyo, Japan: Hara-Shobo, 1975), excerpts from Section 5, “The Emperor made go-seidan [= the sacred decision] – the decision to terminate the war,” 139-149 [translation by Hikaru Tajima]

Zenshiro Hoshina, a senior naval official, attended the conference and prepared a detailed account. With Prime Minister Suzuki presiding, each of the ministers had a chance to state their views directly to Hirohito. While Army Minister Anami tacitly threatened a coup (“civil war”), the emperor accepted the majority view that the reply to the Potsdam declaration should include only one condition not the four urged by “Big Six.” Nevertheless, the condition that Hirohito accepted was not the one that foreign minister Togo had brought to the conference. What was at stake was the definition of the kokutai (national policy). Togo’s proposal would have been generally consistent with a constitutional monarchy because it defined the kokutai narrowly as the emperor and the imperial household. What Hirohito accepted, however, was a proposal by the extreme nationalist Kiichiro Hiranuma which drew upon prevailing understandings of the kokutai : the “mythical notion” that the emperor was a living god. “This was the affirmation of the emperor’s theocratic powers, unencumbered by any law, based on Shinto gods in antiquity, and totally incompatible with a constitutional monarchy.” Thus, the Japanese response to the Potsdam declaration opposed “any demand which prejudices the prerogatives of his Majesty as a sovereign ruler.” This proved to be unacceptable to the Truman administration. [63]

Document 76

Document 77A

The first Japanese surrender offer was intercepted shortly before Tokyo broadcast it. This issue of the diplomatic summary also includes Togo’s account of his notification of the Soviet declaration of war, reports of Soviet military operations in the Far East, and intercepts of French diplomatic traffic.

Document 77B

A full translation of the surrender offer was circulated separately. The translations differ but they convey the sticking point that prevented U.S. acceptance: Tokyo’s condition that the allies not make any “demand which prejudices the prerogatives of His Majesty as a sovereign ruler.”

Document 78

Papers of Henry A. Wallace, Special Collections Department, University of Iowa Libraries, Iowa City, Iowa (copy courtesy of Special Collections Department)

Note: The second page of the diary entry includes a newspaper clipping of the Associated Press’s transmission of the Byrnes note. Unfortunately, AP would not authorize the Archive to reproduce this item without payment. Therefore, we are publishing an excised version of the entry, with a link to the Byrnes note .

Document 79

Document 80

Stimson’s account of the events of 10 August focused on the debate over the reply to the Japanese note, especially the question of the Emperor’s status. The U.S. reply , drafted during the course of the day, did not explicitly reject the note but suggested that any notion about the “prerogatives” of the Emperor would be superceded by the concept that all Japanese would be “Subject to the Supreme Commander of the Allied Powers.” The language was ambiguous enough to enable Japanese readers, upon Hirohito’s urging, to believe that they could decide for themselves the Emperor’s future role. Stimson accepted the language believing that a speedy reply to the Japanese would allow the United States to “get the homeland into our hands before the Russians could put in any substantial claim to occupy and help rule it.” If the note had included specific provision for a constitutional monarchy, Hasegawa argues, it would have “taken the wind out of the sails” of the military faction and Japan might have surrendered several days earlier, on August 11 or 12 instead of August 14. [65]

Document 81

Clemson University Libraries, Special Collections, Clemson, SC; Mss 243, Walter Brown Papers, box 68, folder 13, “Transcript/Draft B

Brown recounted Byrnes’ debriefing of the 10 August White House meeting on the Japanese peace offer, an account which differed somewhat from that in the Stimson diary. According to what Byrnes told Brown, Truman, Stimson, and Leahy favored accepting the Japanese note, but Byrnes objected that the United States should “go [no] further than we were willing to go at Potsdam.” Stimson’s account of the meeting noted Byrnes’ concerns (“troubled and anxious”) about the Japanese note and implied that he (Stimson) favored accepting it, but did not picture the debate as starkly as Browns's did.

Document 82

George C. Marshall Papers, George C. Marshall Library, Lexington, VA (copy courtesy of Barton J. Bernstein)

Groves informed General Marshall that he was making plans for the use of a third atomic weapon sometime after 17 August, depending on the weather. With Truman having ordered a halt to the atomic bombings [See document 78], Marshall wrote on Grove's memo that the bomb was “not to be released over Japan without express authority from the President.”

Document 83

Library of Congress Manuscript Division, Papers of W. Averell Harriman, box 181, Chron File Aug 10-12, 1945

Document 84

Takashi Itoh, ed., Sokichi Takagi: Nikki to Joho [Sokichi Takagi: Diary and Documents] (Tokyo, Japan: Misuzu-Shobo, 2000), 926-927 [Translation by Hikaru Tajima]

Document 85

National Archives, RG 165, Army Operations OPD, Executive Files 1940-1945, box 12, Exec #2

Document 86

Gaimusho [Ministry of Foreign Affairs], ed., Shusen Shiroku [Historical Record of the End of the War] (Tokyo: Hokuyosha, 1977-1978), vol. 5, 27-35 [Translated by Toshihiro Higuchi]

The Byrnes Note did not break the stalemate at the cabinet level. An account of the cabinet debates on August 13 prepared by Information Minister Toshiro Shimamura showed the same divisions as before; Anami and a few other ministers continued to argue that the Allies threatened the kokutai and that setting the four conditions (no occupation, etc.) did not mean that the war would continue. Nevertheless, Anami argued, “We are still left with some power to fight.” Suzuki, who was working quietly with the peace party, declared that the Allied terms were acceptable because they gave a “dim hope in the dark” of preserving the emperor. At the end of the meeting, he announced that he would report to Hirohito and ask him to make another “Sacred Judgment”. Meanwhile, junior Army officers plotted a coup to thwart the plans for surrender. [68]

Document 87

George C. Marshall Library, Lexington, VA, George C. Marshall Papers (copy courtesy of Barton J. Bernstein)

Document 88

Document 89

Hiroshi [Kaian) Shimomura, Shusenki [Account of the End of the War] (Tokyo, Kamakura Bunko, [1948], 148-152 [Translated by Toshihiro Higuchi]

Frightened by the rapid movement of Soviet forces into Manchuria and worried that the army might launch a coup, the peace party set in motion a plan to persuade Hirohito to meet with the cabinet and the “Big Six” to resolve the stalemate over the response to the Allies. Japan was already a day late in responding to the Byrnes Note and Hirohito agreed to move quickly. At 10:50 a.m., he met with the leadership at the bomb shelter in his palace. This account, prepared by Director of Information Shimomura, conveys the drama of the occasion (as well as his interest in shifting the blame for the debacle to the Army). After Suzuki gave the war party--Umeda, Toyoda, and Anami--an opportunity to present their arguments against accepting the Byrnes Note, he asked the emperor to speak.

Hirohito asked the leadership to accept the Note, which he believed was “well intentioned” on the matter of the “national polity” (by leaving open a possible role for the Emperor). Arguing that continuing the war would reduce the nation “to ashes,” his words about “bearing the unbearable” and sadness over wartime losses and suffering prefigured the language that Hirohito would use in his public announcement the next day. According to Bix, “Hirohito's language helped to transform him from a war to a peace leader, from a cold, aloof monarch to a human being who cared for his people” but “what chiefly motivated him … was his desire to save a politically empowered throne with himself on it.” [70]

Hirohito said that he would make a recording of the surrender announcement so that the nation could hear it. That evening army officers tried to seize the palace and find Hirohito’s recording, but the coup failed. Early the next day, General Anami committed suicide. On the morning of August 15, Hirohito broadcast the message to the nation (although he never used the word “surrender”). A few weeks later, on September 2, 1945 Japanese representatives signed surrender documents on the USS Missouri , in Tokyo harbor. [71]

Document 90

Document 91

The British National Archives, Records of the Foreign and Commonwealth Office, FO 800/461

With the Japanese surrender announcement not yet in, President Truman believed that another atomic bombing might become necessary. After a White House meeting on 14 August, British Minister John Balfour reported that Truman had “remarked sadly that he now had no alternative but to order an atomic bomb to be dropped on Tokyo.” This was likely emotional thinking spurred by anxiety and uncertainty. Truman was apparently not considering the fact that Tokyo was already devastated by fire bombing and that an atomic bombing would have killed the Emperor, which would have greatly complicated the process of surrender. Moreover, he may not have known that the third bomb was still in the United States and would not be available for use for nearly another week. [73] As it turned out, a few hours later, at 4:05 p.m., the White House received the Japanese surrender announcement.

Document 92

Department of Energy Open-Net

Two scientists at Oak Ridge’s Health Division, Henshaw and Coveyou, saw a United Press report in the Knoxville News Sentinel about radiation sickness caused by the bombings. Victims who looked healthy weakened, “for unknown reasons” and many died. Lacking direct knowledge of conditions in Hiroshima and Nagasaki, Henshaw and Coveyou had their own data on the biological effects of radiation and could make educated guesses. After reviewing the impact of various atomic bomb effects--blast, heat, flash radiation (prompt effects from gamma and neutron radiation), and radiation from radioactive substances--they concluded that “it seems highly plausible that a great many persons were subjected to lethal and sub-lethal dosages of radiation in areas where direct blast effects were possibly non-lethal.” It was “probable,” therefore, that radiation “would produce increments to the death rate and “even more probable” that a “great number of cases of sub-lethal exposures to radiation have been suffered.” [74]

Document 93

RG 77, MED Records, Top Secret Documents, File no. 5b

Document 94A

RG 77, Tinian Files, April-December 1945, box 17, Envelope B

See description of document 94B

Document 94B

XII. Eisenhower and McCloy’s Views on the Bombings and Atomic Weapons

Document 95

Document 96

Harry S. Truman Library, President's Secretary's Files, Speech Files, 1945-1953, copy on U.S. National Archives Web Site

On 15 December, President Truman spoke about the atomic bombings in his speech at the annual dinner of the Gridiron Club, organized by bureau chiefs and other leading figures of print media organizations. Besides Truman, guests included New York Governor Thomas Dewey (Republican presidential candidate in 1944 and 1948), foreign ambassadors, members of the cabinet and the Supreme Court, the military high command, and various senators and representatives. The U.S. Marine Band provided music for the dinner and for the variety show that was performed by members of the press. [79]

Truman characterized the Potsdam Declaration as a “fair warning,” but it was an ultimatum. Plainly he was troubled by the devastation and suffering caused by the bombings, but he found it justifiable because it saved the lives of U.S. troops. His estimate of 250,000 U.S. soldiers spared far exceeded that made by General Marshall in June 1945, which was in the range of 31,000 (comparable to the Battle of Luzon) [See Document 26]. By citing an inflated casualty figure, the president was giving a trial run for the rationale that would become central to official and semi-official discourse about the bombings during the decades ahead. [80]

Despite Truman’s claim that he made “the most terrible” decision at Potsdam, he assigned himself more responsibility than the historical record supports. On the basic decision, he had simply concurred with the judgments of Stimson, Groves, and others that the bomb would be used as soon as it was available for military use. As for targeting, however, he had a more significant role. At Potsdam, Stimson raised his objections to targeting Japan’s cultural capital, Kyoto, and Truman supported the secretary’s efforts to drop that city from the target list [See Documents 47 and 48]. [81]

[1] . The World Wide Web includes significant documentary resources on these events. The Truman Library has published a helpful collection of archival documents , some of which are included in the present collection. A collection of transcribed documents is Gene Dannen’s “ Atomic Bomb: Decision .” For a print collection of documents, see Dennis Merrill ed.,  Documentary History of the Truman Presidency: Volume I: The Decision to Drop the Atomic Bomb on Japan  (University Publications of America, 1995). A more recent collection of documents, along with a bibliography, narrative, and chronology, is Michael Kort’s  The Columbia Guide to Hiroshima and the Bomb  (New York: Columbia University Press, 2007). An important  on-line collection focuses on the air-raids of Japanese cities and bases, providing valuable context for the atomic attacks.

[2] . For the early criticisms and their impact on Stimson and other former officials, see Barton J. Bernstein, “Seizing the Contested Terrain of Early Nuclear History: Stimson, Conant, and Their Allies Explain the Decision to Use the Atomic Bomb,”  Diplomatic History  17 (1993): 35-72, and James Hershberg,  James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age  (Stanford, Stanford University Press, 1995), 291-301.

For Stimson’s article, see “The Decision to Use the Atomic Bomb,”  Harper’s  194 (February 1947): 97-107. Social critic Dwight MacDonald published trenchant criticisms immediately after Hiroshima-Nagasaki; see  Politics Past: Essays in Political Criticism  (New York: Viking, 1972), 169-180.

[3] . The proposed script for the Smithsonian exhibition can be seen at Philipe Nobile,

Judgment at the Smithsonian  (New York: Matthews and Company, 1995), pp. 1-127. For reviews of the controversy, see Barton J. Bernstein, “The Struggle Over History: Defining the Hiroshima Narrative,” ibid., 128-256, and Charles T. O’Reilly and William A. Rooney,  The Enola Gay and The Smithsonian  (Jefferson, NC: McFarland and Company, 2005).

[4] . For the extensive literature, see the references in J. Samuel Walker , Prompt and Utter Destruction: Truman and the Use of Atomic Bombs against Japan,  Third Edition (Chapel Hill: University of North Carolina Press, 2016) at 131-136, as well as Walker’s, “Recent Literature on Truman’s Atomic Bomb Decision: A Search for Middle Ground,”  Diplomatic History  29 (April 2005): 311-334. For more recent contributions, see Sean Malloy,  Atomic Tragedy: Henry L. Stimson and the Decision to Use the Bomb Against Japan  (Ithaca: Cornell University Press, 2008), Andrew Rotter,  Hiroshima: The World's Bomb  (New York: Oxford, 2008), Campbell Craig and Sergey Radchenko,  The Atomic Bomb and the Origins of the Cold War  (New Haven, Yale University Press, 2008), Wilson D. Miscamble,  The Most Controversial Decision: Truman, the Atomic Bombs, and the Defeat of Japan  (New York: Cambridge University Press, 2011). Also important to take into account is John Dower’s extensive discussion of Hiroshima/Nagasaki in context of the U.S. fire-bombings of Japanese cities in  Cultures of War: Pearl Harbor/Hiroshima/9-11/Iraq  (New York, W. Norton, 2010), 163-285.

[5] . The editor particularly benefited from the source material cited in the following works: Robert S. Norris,  Racing for the Bomb: General Leslie S. Groves, The Manhattan Project’s Indispensable Man  (South Royalton, VT: Steerforth Press, 2002); Gar Alperovitz,  The Decision to Use the Bomb and the Architecture of an American Myth  (New York: Alfred E. Knopf, 1995); Richard B. Frank , Downfall: The End of the Imperial Japanese Empire  (New York: Random House, 1999), Martin Sherwin,  A World Destroyed: Hiroshima and the Origins of the Arm Race  (New York, Vintage Books, 1987), and as already mentioned, Hasegawa’s  Racing the Enemy: Stalin, Truman, and the Surrender of Japan  (Cambridge, Harvard University Press, 2005 ).  Barton J. Bernstein’s numerous articles in scholarly publications (many of them are listed in Walker’s assessment of the literature) constitute an invaluable guide to primary sources. An article that Bernstein published in 1995, “The Atomic Bombings Reconsidered,”  Foreign Affairs  74 (1995), 135-152, nicely summarizes his thinking on the key issues.   Noteworthy publications since 2015 include Michael D. Gordin and G. John Ikenberry, eds., The Age of Hiroshim a (Princeton: Princeton University Press, 2019); Sheldon Garon, “On the Transnational Destruction of Cities: What Japan and the United States Learned from the Bombing of Britain and Germany in the Second World War,” Past and Present 247 (2020): 235-271; Katherine E. McKinney, Scott Sagan, and Allen S. Weiner, “Why the Atomic Bombing of Hiroshima Would Be Illegal Today,” The Bulletin of the Atomic Scientist s 76 (2020); Gregg Mitchell, The Beginning or the End: How Hollywood and America Learned  to Stop Worrying and Love the Bomb (New York: The New Press, 2020); Steve Olson, The Apocalypse Factory: Plutonium and the Making of the Atomic Age (New York: W.W. Norton, 2020); Neil J. Sullivan, The Prometheus Bomb: The Manhattan Project and Government in the Dark  (Lincoln, NE: University of Nebraska Press/Potomac Books, 2016); Alex Wellerstein; Restricted Data: The History of Nuclear Secrecy in the United States,  (Chicago: University of Chicago Press, forthcoming, 2020), a memoir by a Hiroshima survivor, Taniguchi Sumitero, The Atomic  Bomb on My Back: A Life Story of Survival and Activism (Montpelier, VT: Rootstock Publishing, 2020), and a collection of interviews, Cynthia C. Kelly, ed., The Manhattan Project: The Birth of the Atomic Bomb in the Words of Its Creators, Eyewitnesses, and Historians (Black Dog & Leventhal, 2020).

[6] . Malloy (2008), 49-50. For more on the Uranium Committee, the decision to establish the S-1 Committee, and the overall context, see James G. Hershberg , James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age  (Stanford, Stanford University Press, 1995), 140-154.

[7] . Sean Malloy, “`A Very Pleasant Way to Die’: Radiation Effects and the Decision to Use the Atomic Bomb against Japan,”  Diplomatic History  36 (2012), especially 523. For an important study of how contemporary officials and scientists looked at the atomic bomb prior to first use in Japan, see Michael D. Gordin,  Five Days in August: How World War II Became a Nuclear War  (Princeton: Princeton University Press, 2007).

[8] . Norris, 169.

[9] . Malloy (2008), 57-58.

[10] . See also Norris, 362.

[11] . For discussion of the importance of this memorandum, see Sherwin, 126-127, and Hershberg , James B. Conant , 203-207.

[12] . Alperovitz, 662; Bernstein (1995), 139; Norris, 377.

[13] . Quotation and statistics from Thomas R. Searle, “`It Made a Lot of Sense to Kill Skilled Workers’: The Firebombing of Tokyo in March 1945,  The Journal of Military History  55 (2002):103. More statistics and a detailed account of the raid is in Ronald Schaffer,  Wings of Judgment: American Bombing in World War II  (New York: Oxford University Press, 1985), 130-137.

[14] . Searle, “`It Made a Lot of Sense to Kill Skilled Workers,’” 118. For detailed background on the Army Air Force’s incendiary bombing planning, see Schaffer (1985) 107-127. On Stimson, see Schaffer (1985), 179-180 and Malloy (2008), 54. For a useful discussion of the firebombing of Tokyo and the atomic bombings, see Alex Wellerstein, “Tokyo vs. Hiroshima,”  Restricted Data: The Nuclear Secrecy Blog ,  22 September 2014

[15] . See for example, Bernstein (1995), 140-141.

[16] . For useful discussion of this meeting and the other Target Committee meetings, see Norris, 382-386.

[17] . Malloy, “A Very Pleasant Way to Die,” 531-534.

[18] . Schaffer,  Wings of Judgment , 143-146.

[19] . Alperovitz argues that the possibility of atomic diplomacy was central to the thinking of Truman and his advisers, while Bernstein, who argues that Truman’s primary objective was to end the war quickly, suggests that the ability to “cow other nations, notably the Soviet Union” was a “bonus” effect. See Bernstein (1995), 142.

[20] . Alperovitz, 147; Robert James Maddox,  Weapons for Victory: The Hiroshima Decision Fifty Years Later  (Columbia: University of Missouri Press, 1995), 52; Gabiel Kolko,  The Politics of War: The World and United States Foreign Policy, 1943-1945  (New York: Pantheon Books, 1990), 421-422. As Alperovitz notes, the Davies papers include variant diary entries and it is difficult to know which are the most accurate.

[21] . Malloy (2008), 112

[21A] . Vincent Jones, Manhattan: The Army and the Atomic Bomb (Washington, D.C.: U.S. Army Center of Military History, 1985), 529.

[22] . Bernstein (1995), 146. See also Barton J. Bernstein, “Looking Back: Gen. Marshall and the Atomic Bombing of Japanese Cities,” Arms Control Today , November 2015.

[23] . Bernstein (1995), 144. See also Malloy (2008), at 116-117, including the argument that 1) Stimson was deceiving himself by accepting the notion that a “vital war plant …surrounded by workers’ houses” was a legitimate military target, and 2) that Groves was misleading Stimson by withholding the Target Committee’s conclusions that the target would be a city center.

[24] . Walker (2005), 320.

[25] . Frank Costigliola,  France and the United States: The Cold Alliance Since World War II  (New York, Twayne, 1992), 38-39.

[26] . Barton J. Bernstein, Introduction to Helen S. Hawkins et al. editors,  Toward a Livable World: Leo Szilard and the Crusade for Nuclear Arms Control  (Cambridge: MIT Press, 1987), xxx-xxv; Sherwin, 210-215.

[27] . Herbert P. Bix,  Hirohito and the Making of Modern Japan  (New York: HarperCollins Publishers, 2000), 523.

[28] . Walker (2005), 319-320.

[29] . For a review of the debate on casualty estimates, see Walker (2005), 315, 317-318, 321, 323, and 324-325.

[30] . Hasegawa, 105; Alperovitz, 67-72; Forrest Pogue,  George C. Marshall: Statesman, 1945-1959  (New York: Viking, 1987), 18. Pogue only cites the JCS transcript of the meeting; presumably, an interview with a participant was the source of the McCloy quote.

[31] . Alperovitz, 226; Bernstein, “Understanding the Atomic Bomb and the Japanese Surrender,”  Diplomatic History  19 (1995), 237, note 22.

[32] . Malloy (2008), 123-124.

[33] . Alperovitz, 242, 245; Frank, 219.

[34] . Malloy (2008), 125-127.

[35] . Bernstein, introduction,  Toward a Livable World , xxxvii-xxxviii.

[36] . “Magic” summaries for post-August 1945 remain classified at the National Security Agency. Information from the late John Taylor, National Archives. For background on Magic and the “Purple” code, see John Prados,  Combined Fleet Decoded: The Secret History of American Intelligence and the Japanese Navy in World War II (  New York: Random House, 1995), 161-172 and David Kahn,  The Codebreakers: The Story of Secret Writing  (New York: Scribner, 1996), 1-67.

[37] . Alperovitz, 232-238.

[38] . Maddox, 83-84; Hasegawa, 126-128. See also Walker (2005), 316-317.

[39] . Hasegawa, 28, 121-122.

[40] . Peter Grose,  Gentleman Spy: The Life of Allen Dulles  (Boston: Houghton Mifflin, 1994), 170-174, 248-249.

[41] . David Holloway, “Barbarossa and the Bomb: Two Cases of Soviet Intelligence in World War II,” in Jonathan Haslam and Karina Urbach, eds.,  Secret Intelligence in the European States System, 1918-1989  (Stanford: Stanford University Press, 2014), 63-64. For the inception of the Soviet nuclear program and the role of espionage in facilitating it, see Holloway,  Stalin and the Bomb  (New Haven, Yale University Press, 1994).

[42] . For the distances, see Norris, 407.

[43] . For on-line resources on the first atomic test .

[44] . Bernstein’s detailed commentary on Truman’s diary has not been reproduced here except for the opening pages where he provides context and background.

[45] . Frank, 258; Bernstein (1995), 147; Walker (2005), 322. See also Alex Wellerstein’s “ The Kyoto Misconception ”

[46] . Maddox, 102; Alperovitz, 269-270; Hasegawa, 152-153.

[47] . Hasegawa, 292.

[48] . Bernstein, “Understanding the Atomic Bomb and the Japanese Surrender,”  Diplomatic History  19 (1995), 146-147; Alperovitz, 415; Frank, 246.

[49] . Alperovitz, 392; Frank, 148.

[50] . Alperovitz, 281-282. For Davies at Potsdam, see Elizabeth Kimball MacLean,  Joseph E. Davies: Envoy to the Soviets  (Westport, CT: Praeger, 1992), 151-166

[51] . Hasegawa, 168; Bix, 518.

[52] . Bix, 490, 521.

[53] . Alperovitz, 415; Frank, 246.

[54] . Frank, 273-274; Bernstein, “The Alarming Japanese Buildup on Southern Kyushu, Growing U.S. Fears and Counterfactual Analysis: Would the Planned November 1945 Invasion of Southern Kyushu Have Occurred?”  Pacific Historical Review  68 (1999): 561-609.

[55] . Maddox, 105.

[56] . Barton J. Bernstein, "'Reconsidering the 'Atomic General': Leslie R. Groves,"  The Journal of Military History  67 (July 2003): 883-920. See also Malloy, “A Very Pleasant Way to Die,” 539-540.

[57] . For casualty figures and the experience of people on the ground, see Frank, 264-268 and 285-286, among many other sources. Drawing on contemporary documents and journals, Masuji Ibuse’s novel  Black Rain  (Tokyo, Kodansha, 1982) provides an unforgettable account of the bombing of Hiroshima and its aftermath. For early U.S. planning to detonate the weapon at a height designed to maximize destruction from mass fires and other effects, see Alex Wellerstein, “ The Height of the Bomb .”

[58] . Sadao Asada, “The Shock of the Atomic Bomb and Japan’s Decision to Surrender: A Reconsideration,”  Pacific Historical Review  67 (1998): 101-148; Bix, 523; Frank, 348; Hasegawa, 298. Bix appears to have moved toward a position close to Hasegawa’s; see Bix, “Japan's Surrender Decision and the Monarchy: Staying the Course in an Unwinnable War,”  Japan Focus  . For emphasis on the “shock” of the atomic bomb, see also Lawrence Freedman and Saki Dockrill, “Hiroshima: A Strategy of Shock,” in Saki Dockrill, ed.,  From Pearl Harbor to Hiroshima : the Second World War in Asia and the Pacific, 1941-1945  (New York, St. Martin’s Press, 1994), 191-214. For more on the debate over Japan’s surrender, see Hasegawa’s important edited book,  The End of the Pacific War: A Reappraisal  (Stanford: Stanford University Press, 2007), with major contributions by Hasegawa, Holloway, Bernstein, and Hatano.

[59] . Melvyn P. Leffler, “Adherence to Agreements: Yalta and the Experiences of the Early Cold War,”  International Security  11 (1986): 107; Holloway, “Barbarossa and the Bomb,” 65.

[59a] . For more on these developments, see Asada, "The Shock of the Atomic Bomb and Japan's Decision to Surrender: A Reconsideration," 486-488.

[60] . Hasegawa, 191-192.

[61] . Frank, 286-287; Sherwin, 233-237; Bernstein (1995), 150; Maddox, 148.

[62] . The Supreme War Council comprised the prime minister, foreign minister, army and navy ministers, and army and navy chiefs of staff; see Hasegawa, 72 .

[63] . For the maneuverings on August 9 and the role of the  kokutai , see Hasegawa, 3-4, 205-214

[64] . For Truman’s recognition of mass civilian casualties, see also his  letter to Senator Richard Russell, 9 August 1945.

[65] . Hasegawa, 295.

[66] . For “tug of war,” see Hasegawa, 226-227.

[67] . Hasegawa, 228-229, 232.

[68] . Hasegawa, 235-238.

[69] . Barton J. Bernstein, “Eclipsed by Hiroshima and Nagasaki: Early Thinking about Tactical Nuclear Weapons,”  International Security  15 (Spring 1991): 149-173; Marc Gallicchio, “After Nagasaki: General Marshall’s Plans for Tactical Nuclear Weapons in Japan,”  Prologue  23 (Winter 1991): 396-404. Letters from Robert Messer and Gar Alperovitz, with Bernstein’s response, provide insight into some of the interpretative issues. “Correspondence,”  International Security  16 (Winter 1991/1992): 214-221.

[70] . Bix, “Japan's Surrender Decision and the Monarchy: Staying the Course in an Unwinnable War,”  Japan Focus .

[71] . For Hirohito' surrender speech--the actual broadcast and a translation--see  Japan Times , August 2015.

[72] . Cited by Barton J. Bernstein, “Eclipsed by Hiroshima and Nagasaki: Early Thinking About Tactical Nuclear Weapons,”  International Security  15 (1991) at page 167. Thanks to Alex Wellerstein for the suggestion and the archival link.

[73] . For further consideration of Tokyo and more likely targets at the time, see Alex Wellerstein, “Neglected Niigata,”  Restricted Data: The Nuclear Secrecy Blog, 9 October 2015.

[74] . See Malloy, “A Very Pleasant Way to Die,” 541-542.

[75] . For Groves and the problem of radiation sickness, see Norris, 339-441, Bernstein, “Reconsidering the ‘Atomic General’: Leslie R. Groves,”  Journal of Military History  67 (2003), 907-908, and Malloy, “A Very Pleasant Way to Die,” 513-518 and 539-542

[76] . See Janet Farrell Brodie, “Radiation Secrecy and Censorship after Hiroshima and Nagasaki,”  The Journal of Social History  48 (2015): 842-864.

[77] . For Eisenhower’s statements, see  Crusade in Europe  (Garden City: Doubleday, 1948), 443, and  Mandate for Change  (Garden City: Doubleday, 1963), 312-313. Barton J. Bernstein’s 1987 article, “Ike and Hiroshima: Did He Oppose It?”  The Journal of Strategic Studies  10 (1987): 377-389, makes a case against relying on Eisenhower’s memoirs and points to relevant circumstantial evidence. For a slightly different perspective, see Malloy (2007), 138

[78] . Cited in Barton J. Bernstein, “Truman and the A-Bomb: Targeting Noncombatants, Using the Bomb, and His Defending the "Decision,”  The Journal of Military History  62 (1998), at page 559. Thanks to Alex Wellerstein for the suggestion and the archival link.

[79] . “Truman Plays Part of Himself in Skit at Gridiron Dinner,” and “List of Members and Guests at the Gridiron Show,”  The Washington Post , 16 December 1945.

[80] . For varied casualty figures cited by Truman and others after the war, see Walker,  Prompt and Utter Destruction: Truman and the Use of Atomic Bombs Against Japan , 101-102.

[81] . See also ibid., 59.

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Course: US history   >   Unit 7

• Beginning of World War II
• 1940 - Axis gains momentum in World War II
• 1941 Axis momentum accelerates in WW2
• Pearl Harbor
• FDR and World War II
• Japanese internment
• American women and World War II
• 1942 Tide turning in World War II in Europe
• World War II in the Pacific in 1942
• 1943 Axis losing in Europe
• American progress in the Pacific in 1944
• 1944 - Allies advance further in Europe
• 1945 - End of World War II

The Manhattan Project and the atomic bomb

• The United Nations
• The Second World War
• Shaping American national identity from 1890 to 1945

• The United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki in August 1945, killing 210,000 people—children, women, and men.
• President Truman authorized the use of the atom bombs in an effort to bring about Japan’s surrender in the Second World War . In the days following the bombings Japan surrendered.
• The Manhattan Project was the US government program during World War II that developed and built these first atomic bombs.
• Detonation of these first nuclear bombs signaled arrival of a frightening new Atomic Age .

The Manhattan Project

Hiroshima and nagasaki, was the bombing of hiroshima and nagasaki necessary, what do you think.

• David M. Kennedy, Freedom from Fear: The American People in Depression and War, 1929–1945 (New York: Oxford University Press, 1999), 658-668.
• See Kennedy, Freedom from Fear , 658-668.
• See Ira Katznelson, Fear Itself: The New Deal and The Origins of Our Time (New York: Liveright Publishing, 2013), 349.
• See Katznelson, Fear Itself , 350.
• Katznelson, Fear Itself , 614.

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July 21, 2023

What Was the Manhattan Project?

The top-secret Manhattan Project resulted in the atomic bombs dropped on the Japanese cities of Hiroshima and Nagasaki in 1945

By Tom Metcalfe

Sign marking the explosion of the test of the atomic bomb at the Trinity site, N.M.

Education Images/Universal Images Group via Getty Images

The Manhattan Project was a top-secret program to make the first atomic bombs during World War II. Its results had profound impacts on history: the subsequent nuclear arms race has radically changed the political world order in ways that are still evident today.

Thousands of scientists, including theoretical physicist J. Robert Oppenheimer , took part in the Manhattan Project, often while they and their families were lodged at secret military bases in remote locations. It resulted in the two atomic bombs dropped on the Japanese cities of Hiroshima and Nagasaki in August 1945, which brought World War II to its end and probably killed more than 100,000 people .

“The Manhattan Project harnessed the enormous energy in the nucleus of the atom for the first time,” explains Cynthia Kelly, founder and president of the Atomic Heritage Foundation, a nonprofit dedicated to the history of the project and the atomic age.

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One of the project’s consequences was the creation of terrifying opposing arsenals of nuclear weapons . But it also resulted in innovations from medicine to space exploration and in the science and engineering of civilian nuclear energy, Kelly says.

The U.S. Army Corps of Engineers created the Manhattan Engineer District in June 1942 to hide the development of the atomic bomb during the war—hence that effort’s name of the “Manhattan Project.”

But historian of science Alex Wellerstein explains in an online overview that the project originated in an idea from the late 1930s—that Nazi Germany might build an atomic bomb, so the U.S. should do so first. Historical records reveal that Germany didn’t get far , but the prospect of a Nazi bomb was horrifyingly real.

Several leading researchers worked for wartime Germany, including Werner Heisenberg . Even so, many scientists who favored an American atom bomb, including Hungarian-born physicist Leo Szilard , had fled the Nazis in Europe. had fled the Nazis in Europe. 

In July 1939 Szilard and others enlisted the help of the renowned physicist Albert Einstein , then on holiday on Long Island, N.Y., to support them by writing a letter to President Franklin D. Roosevelt. The Einstein-Szilard letter , as it’s known, changed history. It prompted Roosevelt to convene a committee to investigate the possibility of building an atomic bomb, and 1941 this group became a new committee to  lay the groundwork for the full project.

These early stages involved key contributions from the U.K. and Canada. But in the end, the atomic bomb was mostly an American weapon.

After 1942 the Manhattan Project was the recognized Allied effort to build an atomic bomb. It mainly used uranium ore from a mine in what is now the Democratic Republic of the Congo, which was kept secret from the Germans.

Otherwise the project was conducted in the U.S., primarily at three top-secret towns: Oak Ridge, Tenn., where uranium was enriched until it was radioactive enough for nuclear fission; Hanford, Wash., where reactors transformed uranium into plutonium, an even more powerful nuclear fuel; and Los Alamos, N.M., where Oppenheimer directed the laboratory that designed and built experimental atomic bombs.

There were also dozens of smaller sites . And officials went to extraordinary lengths to keep it all secret.

World War II historian Alexandra Levy says most of the more than 600,000 people involved—including the thousands of scientists, engineers and technicians who worked on the weapons, as well as construction workers and the people who kept the three secret towns going—were deliberately not told their purpose.

“Most of those people did not know that the goal of the project was to build a new type of bomb,” Levy says. “Today, between the Internet and social media, it’s difficult to imagine such a large-scale endeavor remaining secret for long.”

Kelly adds, “We live in a very, very different world. Aside from one or two key senators agreeing to a blank check for the Manhattan Project, Congress and the press were kept in the dark. That would be impossible today.”

The Manhattan Project culminated in the Trinity test in New Mexico on July 16, 1945—the first detonation of a nuclear weapon. By that time, the U.S. had spent around $2.2 billion —the equivalent of around $37 billion today.

But the dangers of a Nazi bomb had faded, and Japan was now the designated target. Although Japan never had an atomic bomb program, the idea of stopping its aggression with a show of awful destruction became fixed among Manhattan Project leaders, science historian Wellerstein says.

He notes that Oppenheimer, then the charismatic director of the Los Alamos laboratory, twice voted in favor of the initial atomic bomb attack on Hiroshima —which killed tens of thousands of civilians—instead of a purely military target.

Oppenheimer is seen as essential to the success of the American atomic bomb project. “He contributed to some of the early scientific breakthroughs of the project,” Levy says. “His great gift was bringing together scientists, engineers and other technicians to collaborate on and solve problems.”

But Oppenheimer was also ambivalent about its results. In recalling his experience at the Trinity test in 1965, he quoted a story from the Hindu scripture the Bhagavad Gita about a prince, reluctant to kill his enemies, who witnessed the transformation of Krishna, an incarnation of the Hindu deity Vishnu: “ Now I am become Death, the destroyer of worlds .”

Oppenheimer was the reluctant prince, not Krishna. “He didn’t want to kill people,” Wellerstein says. “But he knew that nuclear weapons were going to be built anyway, and he felt that he had a duty to do this horrible thing.”

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Hiroshima Atomic Bombing Raising New Questions 75 Years Later

David Welna

Japanese Prime Minister Shinzo Abe bows Thursday in front of a memorial to people who were killed in the 1945 atomic bombing of Hiroshima. Philip Fong/AFP via Getty Images hide caption

Japanese Prime Minister Shinzo Abe bows Thursday in front of a memorial to people who were killed in the 1945 atomic bombing of Hiroshima.

The dawn of the nuclear age began with a blinding, flesh-melting blast directly above the Japanese city of Hiroshima on Aug. 6, 1945. It was 8:16 a.m. on a Monday, the start of another workday in a city of nearly 300,000 inhabitants. An estimated two-thirds of that population — nearly all civilians — would soon be dead.

The dropping by American warplanes of that first atomic bomb, code-named Little Boy -- and another, code-named Fat Man, three days later in Nagasaki — led to Japan's surrender on Aug. 15, 1945, and the end of World War II.

At the time, the morality and legality of those nuclear attacks were hardly the subject of public debate.

"Let there be no mistake; we shall completely destroy Japan's power to make war," President Harry Truman, who ordered the attacks, declared in a speech to the nation hours after the bombing of Hiroshima.

"... If they do not now accept our terms, they may expect a rain of ruin from the air, the like of which has never been seen on this earth."

Opinion: 75 Years On, Remember Hiroshima And Nagasaki. But Remember Toyama, Too

The last surviving member of the crew that flew over Hiroshima that day died in November. Before then, he recalled what he thought while aboard a B-29 named Necessary Evil as the bomb dropped from another warplane, the Enola Gay .

"We had to go out and kill every one of them," former Army 2nd Lt. Russell Gackenbach , who flew as a navigator on both the Hiroshima and Nagasaki missions, told the Voices of the Manhattan Project in 2016.

In a 2018 NPR interview , Gackenbach expressed no second thoughts about the annihilation of most of Hiroshima's inhabitants.

"I do not regret what we did that day," he said. "All war is hell. The Japanese started the war. It was our turn to finish it."

Radio Diaries

Last surviving crew member has 'no regrets' about bombing hiroshima.

But another witness to the 900-foot-wide fireball that heated the air above Hiroshima to 500,000 degrees Fahrenheit has made it her life's mission to eliminate nuclear weapons.

"We atomic bomb survivors are greatly disturbed by the continued modernization of nuclear weapons by the United States and other countries, and your stated willingness to use these instruments of genocide," 88-year-old Setsuko Thurlow wrote to President Trump in a letter published Monday in the Daily Hampshire Gazette . "... Nuclear weapons are not a necessary evil, they are the ultimate evil. It is unacceptable for any state to possess them."

Thurlow was a 13-year-old a mile from ground zero in Hiroshima the day the bomb fell there.

"Although that happened in the morning, it was already very dark, like twilight," she told NPR's Kelly McEvers in 2016. "I could see some dark moving object approaching to me. They happened to be human beings. They just didn't look like human beings. I called them ghosts."

A Survivor's Tale: How Hiroshima Shaped A Japanese-American Family

"They were covered with blood and burned and blackened and swollen, and the flesh was hanging from the bones," the atomic blast survivor recalled. "Parts of their bodies were missing, and some were carrying their own eyeballs in their hands. And as they collapsed, their stomach burst open."

Four years ago, President Barack Obama became the first American head of state to visit the Hiroshima Peace Memorial . He offered condolences, but pointedly did not offer apologies.

"The morning of Aug. 6, 1945, must never fade," Obama told a crowd gathered near the shell of the sole building left standing where the bomb exploded. "That memory allows us to fight complacency. It fuels our moral imagination. It allows us to change."

Pope Francis took a more critical stance during a November visit to that same memorial in Hiroshima.

"Using nuclear power to wage war is today, more than ever, a crime," the pontiff declared, adding it was immoral even to possess nuclear weapons.

Some prominent experts in the law of war are also reexamining the Hiroshima attack.

"There is no question that a dropping of a large nuclear weapon amongst the civilian population is a war crime," Harvard Law School professor Gabriella Blum says. "Under the current laws of war, if you know you are going to impact civilians, you must provide warning, and you must take precautions to avoid harming civilians to the extent possible. There is no doubt none of that was considered, and none of that was seriously weighed in reference to Hiroshima and Nagasaki."

After Hiroshima Bombing, Survivors Sorted Through The Horror

In a similar critical vein, the cover story for the current issue of the Bulletin of Atomic Scientists is titled "Why the Atomic Bombing of Hiroshima Would Be Illegal Today."

"We know that one of the main objectives was to cause as much civilian harm as possible, to create a shock among the civilians," says Stanford Law School professor Allen Weiner, one of the cover story's three authors.

"The bomb in Hiroshima was dropped quite far away from the edge of town where the factories and worker housing was located," Weiner notes, "and one of the great ironies is that those factories and worker housing that were [cited by U.S. officials] in selecting Hiroshima as a target survived the atomic bombing. They were not destroyed."

But Weiner also points out that in 1945 no nations had signed a treaty barring the kind of aerial bombardment of civilians that the U.S. carried out in Hiroshima.

"I'm prepared to really give a quite hardcore hedge and say that in 1945, the atomic bombing of Hiroshima and Nagasaki was not clearly illegal," Weiner says. "Today, it would clearly be illegal."

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The Trinity Test

By: History.com Editors

Updated: July 21, 2023 | Original: April 23, 2010

At the time World War II broke out in Europe, America’s scientific community was fighting to catch up to German advances in the development of atomic power. In the early 1940s, the U.S. government authorized a top-secret program of nuclear testing and development, codenamed “The Manhattan Project.” Its goal was the development of the world’s first atomic bomb. Much of the research and development for the project occurred at a facility built in Los Alamos, New Mexico. In July 1945, Los Alamos scientists successfully exploded the first atomic bomb at the Trinity test site, located in nearby Alamogordo.

The Manhattan Project

Beginning in 1939, some American scientists–many of them refugees of fascist regimes in Europe–advocated the development of ways to use nuclear fission for military purposes. By late 1941, the federal government’s Office of Scientific Research and Development, headed by scientist Vannavar Bush, took control of the project. After the United States entered World War II , the U.S. Army Corps of Engineers was tasked with building the great quantity of necessary plants, laboratories and other research and testing facilities.

Much of the initial research had been performed at Columbia University in New York City, and the top-secret research was thereafter known by the code name Manhattan Project . More than 30 laboratories and sites and more than 130,000 people were eventually involved in different facets of nuclear research and development, with three primary locations–in Oak Ridge, Tennessee ; Richland, Washington ; and Los Alamos, New Mexico–that became virtual top-secret atomic cities.

Did you know? The residents of Los Alamos–known as site or project "Y"–lived highly restricted lives: Their mail was censored, their phone calls were monitored and even their interaction with family members was tightly controlled. All mail and official documents listed the site's location only as P.O. Box 1663, Santa Fe, New Mexico.

How Production Worked

A medium-sized reactor built at Oak Ridge produced uranium-235 and plutonium, both of which would be used as vital components in the atomic bomb. The Oak Ridge facility produced the majority of uranium used to build the “Little Boy” bomb that would be dropped over the Japanese city of Hiroshima in August 1945.

Within a year, the world’s first large-scale plutonium reactor was in service at Hanford, and by early 1945 shipments of enriched plutonium from the plant’s three reactors were being sent to Los Alamos every five days. This material would be used in the first atomic bomb testing, as well as in “Fat Man,” the atomic bomb dropped over Nagasaki.

Finally, The facility at Los Alamos served as the primary “think tank” of the Manhattan Project. Its engineers, led by J. Robert Oppenheimer , were responsible for the final construction, testing and delivery of the bombs.

At 5:30 a.m. on July 16, 1945, Los Alamos scientists detonated a plutonium bomb at a test site located on the U.S. Air Force base at Alamogordo, New Mexico , some 120 miles south of Albuquerque. Oppenheimer chose the name “Trinity” for the test site, inspired by the poetry of John Donne. The test had been scheduled for 4 a.m., but when the time came it was raining, and the appointed hour was pushed back to 5:30.

Tensions ran high at the test site, where those assembled included the scientist Enrico Fermi–who had directed the first nuclear chain reaction in December 1942–U.S. Army Brigadier General Leslie Groves, Bush, Oppenheimer and others.

When the bomb was finally detonated atop a steel tower, an intense light flash and sudden wave of heat was followed by a great burst of sound echoing in the valley. A ball of fire tore up into the sky and then was surrounded by a giant mushroom cloud stretching some 40,000 feet across. With a power equivalent to around 21,000 tons of TNT, the bomb completely obliterated the steel tower on which it rested. The nuclear age had begun.

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The Manhattan Project and the Invention of the Atomic Bomb

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During World War II, American physicists and engineers conducted a race against Nazi Germany to become the first to exploit the newly understood process of nuclear fission for military applications. Their secret endeavor, which lasted from 1942 to 1945, was known as the Manhattan Project.

The effort led to the invention of atomic bombs , including the two that were dropped on the Japanese cities of Hiroshima and Nagasaki, killing or injuring over 200,000 people. These attacks forced Japan to surrender and brought an end to World War II, but they also marked a crucial turning point in the early Atomic Age, raising enduring questions about the implications of nuclear warfare.

The Project

The Manhattan Project was named for the Manhattan, New York, home of Columbia University, one of the initial sites of atomic study in the United States. While the research took place at several secret sites across the U.S., much of it, including the first atomic tests, occurred near Los Alamos, New Mexico.

For the project, the U.S. military teamed with the best minds of the scientific community. Military operations were headed by Brig. Gen. Leslie R. Groves, and physicist  J. Robert Oppenheimer  served as the scientific director, overseeing the project from concept to reality. The Manhattan Project cost the U.S. over $2 billion in just four years.

German Competition

In 1938, German scientists had discovered fission, which occurs when the nucleus of an atom breaks into two equal parts. This reaction releases neutrons that break up more atoms, causing a chain reaction. Since significant energy is released in only millionths of a second, it was thought that fission could cause an explosive chain reaction of considerable force inside a uranium bomb.

Beginning in the late 1930s, a number of scientists, many escaping fascist regimes in Europe, immigrated to the U.S., bringing with them news of this discovery. In 1939, physicist Leo Szilard and other American and recently immigrated scientists tried to warn the U.S. government about this new danger but did not get a response. So Szilard contacted Albert Einstein , one of the best-known scientists of the day.

Einstein, a devoted pacifist, was at first reluctant to contact the government. He knew that he would be asking them to work toward creating a weapon that could potentially kill millions of people. Einstein was eventually swayed by concerns that Nazi Germany would develop the weapon first.

U.S. Government Gets Involved

On August 2, 1939, Einstein wrote a now-famous letter to  President Franklin D. Roosevelt , outlining the potential uses of an atomic bomb and ways to help support American scientists in their research. In response, Roosevelt created the Advisory Committee on Uranium the following October.

Based on recommendations of the committee, the government outlaid $6,000 to buy graphite and uranium oxide for research. Scientists believed that graphite might be able to slow a chain reaction, keeping the bomb's energy somewhat in check.

The project was underway, but progress was slow until one fateful event brought the reality of war to American shores.

Development of the Bomb

On December 7, 1941, the  Japanese military bombed Pearl Harbor , Hawaii, the headquarters of the United States Pacific Fleet. In response, the U.S. declared war on Japan the next day and officially entered World War II .

With the country at war and the realization that the United States was three years behind Nazi Germany, Roosevelt was ready to seriously support U.S. efforts to create an atomic bomb.

Costly experiments began at the University of Chicago, the University of California Berkeley, and Columbia. Reactors, devices designed to initiate and control nuclear chain reactions, were built in Hanford, Washington, and Oak Ridge, Tennessee. Oak Ridge, known as "The Secret City," was also the site of a massive uranium enrichment laboratory and plant to make the nuclear fuel.

Researchers worked simultaneously at all the sites to devise ways to produce the fuel. Physical chemist Harold Urey and his Columbia colleagues built an extraction system based on gaseous diffusion. At Berkeley, the inventor of the cyclotron , Ernest Lawrence, used his knowledge and skills to devise a process for magnetically separating the fuel:  uranium-235 and plutonium-239 isotopes .

Research kicked into high gear in 1942. On December 2, at the University of Chicago,  Enrico Fermi  created the first successful chain reaction in which atoms were split in a controlled environment, renewing hopes that an atomic bomb was possible.

Site Consolidation

Another priority for the Manhattan Project soon became clear: It was becoming too dangerous and difficult to develop nuclear weapons at these scattered universities and towns. Scientists needed an isolated laboratory away from the populace.

In 1942, Oppenheimer suggested the remote area of Los Alamos, New Mexico. Groves approved the site and construction began at the end of that year. Oppenheimer became the director of the Los Alamos Laboratory, which would be known as “Project Y."

Scientists continued to work diligently, but it took until 1945 to produce the first nuclear bomb.

Trinity Test

When Roosevelt died on April 12, 1945, Vice President  Harry S. Truman  became the 33rd president of the United States. Until then, Truman had not been told of the Manhattan Project, but he was quickly briefed on the atomic bomb development.

That summer, a test bomb code-named "The Gadget" was taken to a location in the New Mexico desert known as Jornada del Muerto, Spanish for "Journey of the Dead Man." Oppenheimer code-named the test “Trinity,” a reference to a poem by John Donne.

Everyone was anxious: Nothing of this magnitude had been tested before. No one knew what to expect. While some scientists feared a dud, others feared the end of the world.

At 5:30 a.m. on July 16, 1945, scientists, Army personnel, and technicians donned special goggles to watch the beginning of the Atomic Age. The bomb was dropped.

There was a forceful flash, a wave of heat, a stupendous shock wave, and a mushroom cloud extending 40,000 feet into the atmosphere. The tower from which the bomb was dropped disintegrated, and thousands of yards of surrounding desert sand was turned into a brilliant jade green radioactive glass.

The bomb was a success.

The bright light from the Trinity test stood out in the minds of everyone within hundreds of miles of the site that morning. Residents in faraway neighborhoods said the sun rose twice that day. A blind girl 120 miles from the site said she saw the flash.

The men who created the bomb were astonished. Physicist Isidor Rabi expressed worry that mankind had become a threat to upset the equilibrium of nature. The test brought to Oppenheimer's mind a line from the Bhagavad Gita: "Now I am become death, the destroyer of worlds." Physicist Ken Bainbridge, the test director, told Oppenheimer, "Now we're all sons of bitches."

The unease among many witnesses led some to sign petitions arguing that this terrible thing they had created could not be let loose in the world. Their protests were ignored.

2 A-Bombs End World War II

Germany surrendered on May 8, 1945, two months before the Trinity test. Japan refused to surrender, despite threats from Truman that terror would fall from the sky.

The war had lasted six years and involved most of the globe, resulting in the deaths of 61 million people and the displacement of countless others. The last thing the U.S. wanted was a ground war with Japan, so the decision was made to drop an atomic bomb .

On August 6, 1945, a bomb named “Little Boy” for its relatively small size was  dropped on Hiroshima, Japan, by the Enola Gay. Robert Lewis, co-pilot of the B-29 bomber, wrote in his journal moments later, "My God, what have we done?"

The target of Little Boy was the Aioi Bridge, which spanned the Ota River. At 8:15 that morning the bomb was dropped, and by 8:16 over 66,000 people near ground zero were dead. Some 69,000 more were injured, most burned or suffering from radiation sickness, from which many would later die.

This single atomic bomb produced absolute devastation. It left a "total vaporization" zone of one-half mile in diameter. The "total destruction" area extended to one mile, while the impact of a "severe blast" was felt for two miles. Anything flammable within two and a half miles was burned, and blazing infernos were seen up to three miles away.

On August 9, after Japan still refused to surrender, a second bomb was dropped, a plutonium bomb named “Fat Man” after its round shape. The bomb's target was the city of Nagasaki, Japan. Over 39,000 people were killed and 25,000 injured.

Japan surrendered on August 14, 1945, bringing an end to World War II.

The deadly impact of the atomic bomb was immediate, but the effects would last for decades. The fallout caused radioactive particles to rain on Japanese who had survived the blast, and more lives were lost to radiation poisoning.

Survivors of the bombs passed radiation on to their descendants. The most prominent example was an alarmingly high rate of leukemia among their children.

The bombings at Hiroshima and Nagasaki revealed the true destructive power of these weapons. Though countries throughout the world have continued to develop nuclear weapons, there have also been movements to promote nuclear disarmament , and anti-nuclear treaties have been signed by major world powers.

• " Manhattan Project ." Encyclopaedia Britannica.
• Timeline of World War II From 1939 to 1945
• Comparing the Hydrogen Bomb and the Atomic Bomb
• The Atomic Bombing of Hiroshima and Nagasaki
• Biography of J. Robert Oppenheimer, Director of the Manhattan Project
• What Is Nuclear Disarmament?
• Leo Szilard, Creator of Manhattan Project, Opposed Use of Atomic Bomb
• The Art of Atomic Diplomacy
• Hanford Nuclear Bomb Site: Triumph and Disaster
• Biography of Hans Bethe
• World War II: Potsdam Conference
• An Overview of the Key Events of World War II
• Niels Bohr and the Manhattan Project
• Ten Facts About Harry Truman
• An Overview of World War II
• When and How Did World War II End?
• The Manhattan Project Timeline

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The Manhattan Project

• Manhattan Project History

The Manhattan Project was the result of an enormous collaborative effort between the U.S. government and the industrial and scientific sectors during World War II. Here is a brief summary of the Anglo-American effort to develop an atomic bomb during its World War II and its legacies today.

Preliminary Organization

The story of the Manhattan Project began in 1938, when German scientists Otto Hahn and Fritz Strassmann inadvertently  discovered nuclear fission . A few months later, Albert Einstein and Leo Szilard sent a letter to President Roosevelt warning him that Germany might try to build an atomic bomb. In response, FDR formed the Uranium Committee, a group of top military and scientific experts to determine the feasibility of a nuclear chain reaction.

Nevertheless, initial research moved slowly until the spring of 1941, when the MAUD Committee (essentially the British equivalent to the Uranium Committee) issued a report affirming that an atomic bomb was possible and urging cooperation with the United States. The U.S. government responded by reorganizing its atomic research under the S-1 Committee , which was in turn under the jurisdiction of the newly created Office of Scientific Research and Development, led by Vannevar Bush . As the project progressed from research to development, however, Bush realized that the S-1 Committee did not have the resources for full-scale construction, eventually opting to turn to the Army for support.

Preliminary Research

Meanwhile, at Columbia University, a team of scientists, including  Enrico Fermi ,  Leo Szilard ,  Walter Zinn , and  Herbert Anderson , conducted experiments using chain-reacting nuclear “piles” to measure the neutron emission from fission. Production was moved to the Metallurgical Laboratory at the University of Chicago in February 1942. On December 2, Chicago Pile-1 went critical, creating the world’s first self-sustaining chain reaction. The experiment not only proved that nuclear energy could generate power, but also showed a viable method to produce plutonium.

Forming the Manhattan Project

The Manhattan Project was officially created on August 13, 1942. The name itself, “Manhattan Project,” is commonly thought to be a misnomer, but its first offices were actually in Manhattan, at 270 Broadway. General Leslie R. Groves , who was appointed to head the project, decided to follow the custom of naming Corps of Engineers districts for the city in which they are located. The atomic bomb project thus became known as the Manhattan Engineer District (MED), or Manhattan Project for short.

Its first major funding came in December, when President Roosevelt ordered an initial allotment of $500 million. The headquarters of the project would soon be moved to Washington, D.C., while numerous project sites were scattered across the country.

Project Sites

The Manhattan Project’s weapons research laboratory was located at Los Alamos, New Mexico . Under the direction of J. Robert Oppenheimer , the Los Alamos laboratory would conduct the bulk of the remaining research and construction of the bomb. Physicists, chemists, metallurgists, explosive experts, and military personnel converged in the secret town, which grew to be the home of thousands of project workers. Meanwhile, the Army was charged with supplying, supporting, and guarding the top-secret work being done at Los Alamos.

Another important Manhattan Project site was located at Oak Ridge, Tennessee . By this time, the Manhattan Project was pursuing both a uranium and a plutonium based atomic bomb. Oak Ridge was thus the home of the uranium enrichment plants, K-25, Y-12, and S-50, and the pilot plutonium production reactor, the X-10 Graphite Reactor. Equally important was the site at Hanford, Washington , where the full-scale plutonium production plant, the B Reactor, was constructed, and was eventually joined by other reactors.

Dozens of other sites were also involved with the Manhattan Project. In Cambridge, Massachusetts , scientists conducted further research at Harvard University and the Massachusetts Institute of Technology. In Dayton, Ohio , the Manhattan Project tasked the Monsanto Chemical Company with separating and purifying the radioactive element polonium (Po-210), which was to be used as the initiator for the atomic bombs. Even in Canada , the Manhattan Project coordinated its efforts with the Montreal Laboratory and the Chalk River Nuclear Laboratories in Ontario, the site for one of the world’s first heavy water nuclear reactors. Meanwhile, the 509 th Composite Group of the Army Air Forces, which would drop the atomic bombs on Japan, trained at Wendover Airfield in Utah and in Cuba before shipping out to the launching point for the atomic bomb attacks at Tinian Island in the Pacific.

It is estimated that more than 600,000 people worked on the project . For a list of more Manhattan Project sites, please click here .

Producing Results

On July 16, the atomic age officially began when the world’s first atomic bomb was tested at the Trinity site in the New Mexico desert. The “Gadget” plutonium bomb exploded with approximately 20 kilotons of force and produced a mushroom cloud that rose eight miles high and left a crater that was ten feet deep and over 1,000 feet wide.

On August 6, the United States dropped its first atomic bomb on Hiroshima . Known as “Little Boy,” the uranium gun-type bomb exploded with about thirteen kilotons of force. The B-29 plane that carried Little Boy from Tinian Island in the western Pacific to Hiroshima was known as the Enola Gay, after pilot Paul Tibbets’ mother. Between 90,000 and 166,000 people are believed to have died from the bomb in the four-month period following the explosion. The U.S. Department of Energy has estimated that after five years there were perhaps 200,000 or more fatalities as a result of the bombing, while the city of Hiroshima has estimated that 237,000 people were killed directly or indirectly by the bomb’s effects, including burns, radiation sickness, and cancer.

Three days later, a second atomic bomb was dropped on Nagasaki – a 21-kiloton plutonium device known as “Fat Man.” It is estimated that between 40,000 and 75,000 people died immediately following the atomic explosion, while another 60,000 people suffered severe injuries. Total deaths by the end of 1945 may have reached 80,000. Japan surrendered on August 14.

The debate  over the bomb – whether there should have been a test demonstration, whether the Nagasaki bomb was necessary, and more – continues to this day.

Finally, the Manhattan Project remains to this day a controversial subject. For example, the proposed Enola Gay Exhibition at the National Air and Space Museum (NASM) in 1995 was ultimately canceled. In 2015, however, the U.S. Congress established the Manhattan Project National Historical Park at Oak Ridge, Hanford, and Los Alamos. The new park works to interpret the Manhattan Project’s history and legacy for our world today.

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70 years after Hiroshima, opinions have shifted on use of atomic bomb

On Aug. 6, 1945, the United States dropped an atomic bomb on the Japanese city of Hiroshima, killing tens of thousands of people – many instantly, others from the effects of radiation. Death estimates range from 66,000 to 150,000 .

This first use of a nuclear weapon by any nation has long divided Americans and Japanese. Americans have consistently approved of this attack and have said it was justified. The Japanese have not. But opinions are changing: Americans are less and less supportive of their use of atomic weapons, and the Japanese are more and more opposed.

In 1945, a Gallup poll immediately after the bombing found that 85% of Americans approved of using the new atomic weapon on Japanese cities. In 1991, according to a Detroit Free Press survey conducted in both Japan and the U.S., 63% of Americans said the atomic bomb attacks on Japan were a justified means of ending the war, while only 29% thought the action was unjustified. At the same time, only 29% of Japanese said the bombing was justified, while 64% thought it was unwarranted.

But a 2015 Pew Research Center survey finds that the share of Americans who believe the use of nuclear weapons was justified is now 56%, with 34% saying it was not. In Japan, only 14% say the bombing was justified, versus 79% who say it was not.

Not surprisingly, there is a large generation gap among Americans in attitudes toward the bombings of Hiroshima. Seven-in-ten Americans ages 65 and older say the use of atomic weapons was justified, but only 47% of 18- to 29-year-olds agree. There is a similar partisan divide: 74% of Republicans but only 52% of Democrats see the use of nuclear weapons at the end of World War II as warranted.

In the years since WWII, two issues have fueled a debate over America’s use of nuclear weapons against Japan: Did Washington have an alternative to the course it pursued – the bombing of Hiroshima followed by dropping a second atomic weapon on Nagasaki on Aug. 9 – and should the U.S. now apologize for these actions?

In September 1945, the National Opinion Research Center at the University of Chicago asked Americans what they would have done if they had been the one to decide whether or not to use the atomic bomb against Japan. At the time, a plurality of Americans supported the course chosen by the Truman administration: 44% said they would have bombed one city at a time, and another 23% would have wiped out cities in general – in other words, two-thirds would have bombed some urban area. Just 26% would have dropped the bomb on locations that had no people. And only 4% would not have used the bomb.

By 1995, 50 years after Hiroshima and Nagasaki, support for an alternative to the bombing had grown. Gallup asked Americans whether, had the decision been left up to them, they would have ordered the bombs to be dropped, or tried some other way to force the Japanese to surrender. Half the respondents said they would have tried some other way, while 44% still backed using nuclear weapons.

But this decline in American support for the use of atomic bombs against Japanese cities did not mean Americans thought they had to apologize for having done so. In that same Gallup survey, 73% said the U.S. should not formally apologize to Japan for the atom bomb attacks on Hiroshima and Nagasaki. Only 20% supported an official apology.

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Beyond the bomb: Atomic research changed medicine, biology

Princeton University historian Angela Creager spent more than a decade researching early efforts to transform knowledge and technology developed for the Manhattan Project to peaceful uses. The research culminated in a new book, "Life Atomic: Radioisotopes in Science and Medicine," which details how that effort made possible important breakthroughs in medicine and biology.

Video stills from Nick Barberio, Office of Communications

Even before the end of World War II, scientists working on the Manhattan Project saw a future for their work beyond military might. 

A new book by Princeton University historian Angela Creager explains how knowledge and technology that grew out of the secret U.S.-led effort to build atomic bombs delivered on that promise — making possible important breakthroughs in medicine and biology. 

In this video , Creager discusses those breakthroughs and how they happened.

Play the "Insights With Angela Creager" video.

"Generally when both ordinary people and scholars have thought about the legacy of the Manhattan Project, we thought about the way in which physics and engineering were put to military use. We thought about a destructive legacy, the arms race, the Cold War," said Creager, the Philip and Beulah Rollins Professor of History . "Part of what I discovered was that atomic energy had just as much of a legacy in some of the fields we think of as peaceable as it did in military uses."

The book, "Life Atomic: Radioisotopes in Science and Medicine," is the culmination of more than a decade of research by Creager, who traveled across the country to study unpublished government documents and the papers of scientists involved in military and civilian research.

Creager, who joined the Princeton faculty in 1994, teaches undergraduate and graduate courses on the history of science, the history of biology, gender and science, and technology and science. In 1998, she received the President's Award for Distinguished Teaching at Princeton. Creager is also the author of "The Life of a Virus: Tobacco Mosaic Virus as an Experimental Model, 1930-1965." She is a fellow of the American Association for the Advancement of Science and president of the History of Science Society. Creager earned a Ph.D. from the University of California-Berkeley and a bachelor's degree from Rice University.

Among the breakthroughs linked to atomic research that Creager highlights in "Life Atomic":

• treatments for cancer, especially using cobalt-60;
• diagnostic tests still used widely in medicine;
• an understanding of metabolic pathways, such as that for photosynthesis;
• a clearer picture of how the human body absorbs and uses substances such as iron;
• the modern understanding of ecosystems as environments in which matter and energy flow through living and nonliving components.

These advances were made possible by the availability of radioisotopes, which are radioactive isotopes, or variants, of stable atoms. In the post-World War II era, the U.S. government produced radioisotopes in some of the same nuclear reactors that had been built to produce material for nuclear weapons. The radioisotopes were promoted by the government and sold at a discount to laboratories, hospitals and companies, Creager said.

Radioisotopes quickly gained acceptance as both medical therapies and radiotracers, she said.

"Tracer uses are when you replace one atom of a compound with a particular radiolabeled atom so that you can follow that label through the ordinary chemical or biological processes the compound goes through," Creager said. "So radiotracing was very widely applicable to study biochemistry, physiology, endocrinology and eventually ecology. Basically anything where a chemical compound is in motion, radiotracing is a way to look at change over time, and look at chemical transformations."

Creager said the study of photosynthesis offered a good example of how radiotracing was used. Researchers grew algae in a glass container exposed to bright light. They added carbon dioxide labeled with the radioisotope carbon-14 and let the algae take up some of the carbon dioxide. They then examined how the radiolabeled carbon had moved from one compound to another through the chemical reactions of photosynethsis.

"Even by the late 1940s, it was already apparent this could be used to crack open the photosynthetic pathway, which really hadn't been understood before," Creager said.

In a similar way, animals, and later humans, were fed food containing a radioisotope of iron in experiments that aided the understanding of iron uptake, Creager said.

The book also traces changes in the perceptions of scientists and the public about the risks of radiation. An investigation by a presidential panel in the 1990s detailed the ways in which research subjects — sometimes without their knowledge — were exposed to radiation during the postwar period. This included, for instance, pregnant women in experiments with radioiron. Creager said documents declassified in the wake of that investigation aided her research.

"Now we think the government should be involved at some level in protecting civilians from exploitation by a medical establishment that is eager for research subjects, but in the 1950s the thought was that physicians should be trusted to regulate themselves," Creager said. "The human research using radioisotopes wasn't atypical of other types of medical research at the time, even though we may look back and think it was a really bad idea."

Creager's research has carried over to the classroom. For example, she once taught a junior seminar titled "Atomic Legacies." As part of the class, eight students traveled with Creager to the National Archives outside Washington, D.C., for two days of research.

"The junior papers that were produced from this seminar were terrific, and it was also a great experience to go with them to the archives and, in many cases, have the students encounter unpublished sources for the first time and think about how they might go into writing a historical account," Creager said.

Creager's research for "Life Atomic" was supported by grants from the National Science Foundation, the National Institutes of Health, the National Endowment for the Humanities and Princeton University.

She has begun work on her next project, which examines changing ideas about environmental carcinogens from the 1960s through the 1980s. Many of those ideas, she said, were first shaped by research on radiation.

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Algal library lends insights into genes for photosynthesis .

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'Insights With Angela Creager' .

A new book by Princeton University historian Angela Creager explains how knowledge and technology that grew out of the Manhattan Project paved the way for important breakthroughs in medicine and biology. In this video, Creager describes the great hopes for atomic research in the 1940s and '50s and how those hopes were later tempered by  concerns about radiation exposure.

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What is a nuclear weapon?

A nuclear weapon is a device designed to release energy in an explosive manner as a result of nuclear fission, nuclear fusion, or a combination of the two processes.

Are there treaties to control the proliferation of nuclear weapons?

Concerns about the devastating effects of nuclear weapons have driven governments to negotiate arms control agreements. Some of the earliest ones include the Nuclear Test-Ban Treaty of 1963 and the Treaty on the Non-proliferation of Nuclear Weapons of 1968.

When was a nuclear weapon first tested?

The first test of a nuclear weapon occurred in the United States on July 16, 1945, at the Alamogordo Bombing Range in south-central New Mexico. The test was code-named Trinity.

The Soviet Union had the most nuclear weapons during the Cold War. The Soviet stockpile reached a peak of about 33,000 operational warheads in 1988, with an additional 10,000 previously deployed warheads that had been retired but not dismantled. The U.S. stockpile reached its peak in 1966 with more than 32,000 nuclear warheads.

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nuclear weapon , device designed to release energy in an explosive manner as a result of nuclear fission , nuclear fusion , or a combination of the two processes. Fission weapons are commonly referred to as atomic bombs . Fusion weapons are also referred to as thermonuclear bombs or, more commonly, hydrogen bombs; they are usually defined as nuclear weapons in which at least a portion of the energy is released by nuclear fusion.

Nuclear weapons produce enormous explosive energy. Their significance may best be appreciated by the coining of the words kiloton (1,000 tons) and megaton (1,000,000 tons) to describe their blast energy in equivalent weights of the conventional chemical explosive TNT . For example, the atomic bomb dropped on Hiroshima , Japan , in 1945, containing only about 64 kg (140 pounds) of highly enriched uranium , released energy equaling about 15 kilotons of chemical explosive. That blast immediately produced a strong shock wave , enormous amounts of heat, and lethal ionizing radiation . Convection currents created by the explosion drew dust and other debris into the air, creating the mushroom-shaped cloud that has since become the virtual signature of a nuclear explosion. In addition, radioactive debris was carried by winds high into the atmosphere, later to settle to Earth as radioactive fallout . The enormous toll in destruction, death, injury, and sickness produced by the explosions at Hiroshima and, three days later, at Nagasaki was on a scale never before produced by any single weapon . In the decades since 1945, even as many countries have developed nuclear weapons of far greater strength than those used against the Japanese cities, concerns about the dreadful effects of such weapons have driven governments to negotiate arms control agreements, such as the Nuclear Test-Ban Treaty of 1963 and the Treaty on the Non-proliferation of Nuclear Weapons of 1968. Among military strategists and planners, the very presence of these weapons of unparalleled destructive power has created a distinct discipline , with its own internal logic and set of doctrines, known as nuclear strategy .

The first nuclear weapons were bombs delivered by aircraft. Later, warheads were developed for strategic ballistic missiles, which have become by far the most important nuclear weapons. Smaller tactical nuclear weapons have also been developed, including ones for artillery projectiles, land mines , antisubmarine depth charges , torpedoes , and shorter-range ballistic and cruise missiles .

By far the greatest force driving the development of nuclear weapons after World War II (though not by any means the only force) was the Cold War confrontation that pitted the United States and its allies against the Soviet Union and its satellite states. During this period, which lasted roughly from 1945 to 1991, the American stockpile of nuclear weapons reached its peak in 1966, with more than 32,000 warheads of 30 different types. During the 1990s, following the dissolution of the Soviet Union and the end of the Cold War, many types of tactical and strategic weapons were retired and dismantled to comply with arms control negotiations, such as the Strategic Arms Reduction Talks , or as unilateral initiatives . By 2010 the United States had approximately 9,400 warheads of nine types, including two types of bombs, three types for intercontinental ballistic missiles (ICBMs), two types for submarine-launched ballistic missiles (SLBMs), and two types for cruise missiles . Some types existed in several modifications. Of these 9,400 warheads, an estimated 2,468 were operational (that is, mated to a delivery system such as a missile); the rest were either spares held in reserve or retired warheads scheduled to be dismantled. Of the 2,468 operational warheads, approximately 1,968 were deployed on strategic (long-range) delivery systems, and some 500 were deployed on nonstrategic (short-range) systems. Of the 500 nonstrategic warheads in the U.S. arsenal, about 200 were deployed in Europe.

The Soviet nuclear stockpile reached its peak of about 33,000 operational warheads in 1988, with an additional 10,000 previously deployed warheads that had been retired but had not been taken apart. After the disintegration of the Soviet Union, Russia accelerated its warhead dismantlement program, but the status of many of the 12,000 warheads estimated to remain in its stockpile in 2010 was unclear. Given limited Russian resources and lack of legitimate military missions, only about 4,600 of these 12,000 warheads were serviceable and maintained enough to be deployed. Of the 4,600 operational warheads, some 2,600 were deployed on strategic systems and some 2,000 on nonstrategic systems. A global security concern is the safety of Russia ’s intact warheads and the security of nuclear materials removed from dismantled warheads.

Beginning in the 1990s, the arsenals of the United Kingdom , France , and China also underwent significant change and consolidation. Britain eliminated its land-based army, tactical naval, and air nuclear missions, so that its arsenal, which contained some 350 warheads in the 1970s, had just 225 warheads in 2010. Of these, fewer than 160 were operational, all on its ballistic missile submarine fleet. Meanwhile, France reduced its arsenal from some 540 operational warheads at the end of the Cold War to about 300 in 2010, eliminating several types of nuclear weapon systems. The Chinese stockpile remained fairly steady during the 1990s and then started to grow at the beginning of the 21st century. By 2010 China had about 240 warheads in its stockpile, some 180 of them operational and the rest in reserve or retirement.

Israel maintained an undeclared nuclear stockpile of 60 to 80 warheads, but any developments were kept highly secret. India was estimated to have 60 to 80 assembled warheads and Pakistan about 70 to 90. Most of India’s and Pakistan’s warheads were thought not to be operational, though both countries—rivals in the incipient arms race on the Indian subcontinent—were thought to be increasing their stockpiles. North Korea , which joined the nuclear club in 2006, may have produced enough plutonium by 2010 for as many as 8 to 12 warheads, though it was not clear that any of these was operational.

Nuclear Weapons

By: Bastian Herre , Pablo Rosado , Max Roser and Joe Hasell

This page was first published in August 2013 and last revised in February 2024.

The world’s nuclear powers have more than 12,000 nuclear warheads. These weapons can kill millions directly and, through their impact on agriculture, likely have the potential to kill billions .

Nuclear weapons killed between 110,000 and 210,000 people when the United States used them against the Japanese cities of Hiroshima and Nagasaki in August 1945. 1 They have come close to being used again more than a dozen times since.

This is why countries have worked to limit the proliferation and number of nuclear weapons.

On this page, you can find writing, visualizations, and data on how many states have nuclear weapons, how many warheads they possess, how many oppose them, and how this has changed over time.

For an overview of the risks of nuclear weapons – and how they can be reduced – you can read the following essay:

Nuclear weapons: Why reducing the risk of nuclear war should be a key concern of our generation

The consequences of nuclear war would be devastating. Much more should – and can – be done to reduce the risk that humanity will ever fight such a war

Related topics

Biological and Chemical Weapons

Which countries have pursued, possessed, or used biological and chemical weapons? Which countries have sought to eliminate them?

War and Peace

How common are armed conflict and peace between and within countries? How is this changing over time? Explore research and data on war and peace.

Military Personnel and Spending

How large are countries’ militaries? How much do they spend on their armed forces? Explore global data on military personnel and spending.

See all interactive charts on nuclear weapons ↓

Few countries possess nuclear weapons, but some have large arsenals

Nine countries currently have nuclear weapons: Russia, the United States, China, France, the United Kingdom, Pakistan, India, Israel, and North Korea.

These nuclear powers differ a lot in how many nuclear warheads they have. The chart shows that while most have dozens or a few hundred warheads, Russia and the United States have thousands of them.

The chart also shows that the warheads differ in how — and how quickly — they can be used: some are designed for strategic use away from the battlefield, such as against arms industries or infrastructure, while others are for nonstrategic, tactical use on the battlefield.

And while some warheads are not deployed, or even retired and queued for dismantlement, a substantial share of them is deployed on ballistic missiles or bomber bases and can be used quickly.

A lof of countries have given up obtaining nuclear weapons

The number of countries that possess nuclear weapons has never been higher. Only one country — South Africa — entirely dismantled its arsenal .

But, as the chart shows, many more states considered or pursued nuclear weapons, and almost all of them stopped.

In the late 1970s, more than a dozen countries considered or worked to acquire them. Recently, only Syria has considered nuclear weapons and only Iran has pursued building them .

The number of nuclear weapons has declined substantially since the end of the Cold War

After increasing for almost half a century after their creation in the 1940s, nuclear arsenals reached over 60,000 warheads in 1986.

Since then we have seen a reversal of this trend, as the chart shows. The nuclear powers reduced their arsenals a lot in the following decades, and the number of warheads fell below 20,000 in the 2010s.

The decline has slowed since then, and the total stockpile still consists of more than 10,000 warheads. Some countries have also been expanding their arsenals.

The destructiveness of nuclear arsenals has declined

A simple count of the number of warheads, as shown in the previous chart, does not consider that these weapons differ in their explosive power. It also does not consider that not all of them can be used at once.

The data shown in the following chart attempts to take this into account. It considers the destructiveness and deployment of nuclear warheads to arrive at an estimate of the explosive power of nuclear weapons deliverable in a first strike.

We see that the United States rapidly developed much more powerful warheads in the 1950s. The Soviet Union increased the destructiveness of its weapons more slowly but ultimately reached similar levels.

The destructive potential of first-strike warheads peaked at more than 15,000 Mt in the early 1980s. This amounts to more than a million Hiroshima bombs. At this peak, first-strike weapons could destroy more than 40% of the total urban land worldwide.

However, the destructiveness of first strikes has been steadily declining for decades, for both the United States and the Soviet Union/Russia.

Yet, it has still been more than 2,500 Mt, with the potential to directly destroy almost 7% of the total urban land worldwide.

Nuclear weapons tests have almost stopped

The nuclear weapons states frequently tested their warheads in the past, but tests now have almost ended.

The chart shows that they peaked in 1962 at 178 tests, mostly conducted by the United States and the Soviet Union. These tests harmed the environment and people, especially indigenous communities.

Tests decreased later during the Cold War and have been nearly absent in the last two decades. The only country that has recently tested nuclear weapons is North Korea.

Nuclear weapons have come close to being used a dozen times since World War II

After killing between 110,000 and 210,000 people in Hiroshima and Nagasaki in 1945, nuclear weapons have come close to being used more than a dozen times again. 1

The chart below shows a timeline of such close calls. 2 We can see that some of them have been accidental, while others have been deliberate.

You can learn more in our article on the risks of nuclear weapons.

Many countries want to limit or abolish nuclear weapons

Countries have sought to reduce the threat posed by nuclear weapons through international cooperation.

Most countries have approved the Partial and Comprehensive Nuclear-Test-Ban Treaties, which seek an end to nuclear weapons tests.

The same goes for the Nuclear Non-Proliferation Treaty, whose objective is to prevent the spread of nuclear weapons.

Recently, dozens of countries have approved the Nuclear Prohibition Treaty, whose aim is to end the development and existence of nuclear weapons altogether.

Interactive charts on nuclear weapons

You can find the stories of six survivors — Masakazu Fujii, Wilhelm Kleinsorge, Hatsuyo Nakamura, Terufumi Sasaki, Toshiko Sasaki, and Kiyoshi Tanimoto — in John Hersey’s article Hiroshima .

This list is largely based on Toby Ord’s 2020 book The Precipice. His list can be found in Chapter 4 and Appendix C of his book.

Ord in turn relies mostly on a document from the US Department of Defense from 1981: Narrative Summaries of Accidents Involving US Nuclear Weapons (1950–1980).

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The Devastating Effects of Nuclear Weapons

What can nuclear weapons do? How do they achieve their destructive purpose? What would a nuclear war — and its aftermath — look like? In the article that follows, excerpted from Richard Wolfson and Ferenc Dalnoki-Veress’s book “ Nuclear Choices for the Twenty-First Century ,” the authors explore these and related questions that reveal the most horrifying realities of nuclear war.

A Bomb Explodes: Short-Term Effects

The most immediate effect of a nuclear explosion is an intense burst of nuclear radiation, primarily gamma rays and neutrons. This direct radiation is produced in the weapon’s nuclear reactions themselves, and lasts well under a second. Lethal direct radiation extends nearly a mile from a 10-kiloton explosion. With most weapons, though, direct radiation is of little significance because other lethal effects generally encompass greater distances. An important exception is the enhanced-radiation weapon, or neutron bomb, which maximizes direct radiation and minimizes other destructive effects.

An exploding nuclear weapon instantly vaporizes itself. What was cold, solid material microseconds earlier becomes a gas hotter than the Sun’s 15-million-degree core. This hot gas radiates its energy in the form of X-rays, which heat the surrounding air. A fireball of superheated air forms and grows rapidly; 10 seconds after a 1-megaton explosion, the fireball is a mile in diameter. The fireball glows visibly from its own heat — so visibly that the early stages of a 1-megaton fireball are many times brighter than the Sun even at a distance of 50 miles. Besides light, the glowing fireball radiates heat.

This thermal flash lasts many seconds and accounts for more than one-third of the weapon’s explosive energy. The intense heat can ignite fires and cause severe burns on exposed flesh as far as 20 miles from a large thermonuclear explosion. Two-thirds of injured Hiroshima survivors showed evidence of such flash burns. You can think of the incendiary effect of thermal flash as analogous to starting a fire using a magnifying glass to concentrate the Sun’s rays. The difference is that rays from a nuclear explosion are so intense that they don’t need concentration to ignite flammable materials.

The intense heat can ignite fires and cause severe burns on exposed flesh as far as 20 miles from a large thermonuclear explosion.

As the rapidly expanding fireball pushes into the surrounding air, it creates a blast wave consisting of an abrupt jump in air pressure. The blast wave moves outward initially at thousands of miles per hour but slows as it spreads. It carries about half the bomb’s explosive energy and is responsible for most of the physical destruction. Normal air pressure is about 15 pounds per square inch (psi). That means every square inch of your body or your house experiences a force of 15 pounds. You don’t usually feel that force, because air pressure is normally exerted equally in all directions, so the 15 pounds pushing a square inch of your body one way is counterbalanced by 15 pounds pushing the other way. What you do feel is overpressure , caused by a greater air pressure on one side of an object.

If you’ve ever tried to open a door against a strong wind, you’ve experienced overpressure. An overpressure of even 1/100 psi could make a door almost impossible to open. That’s because a door has lots of square inches — about 3,000 or more. So 1/100 psi adds up to a lot of pounds. The blast wave of a nuclear explosion may create overpressures of several psi many miles from the explosion site. Think about that! There are about 50,000 square inches in the front wall of a modest house — and that means 50,000 pounds or 25 tons of force even at 1 psi overpressure. Overpressures of 5 psi are enough to destroy most residential buildings. An overpressure of 10 psi collapses most factories and commercial buildings, and 20 psi will level even reinforced concrete structures.

People, remarkably, are relatively immune to overpressure itself. But they aren’t immune to collapsing buildings or to pieces of glass hurtling through the air at hundreds of miles per hour or to having themselves hurled into concrete walls — all of which are direct consequences of a blast wave’s overpressure. Blast effects therefore cause a great many fatalities. Blast effects depend in part on where a weapon is detonated. The most widespread damage to buildings occurs in an air burst , a detonation thousands of feet above the target. The blast wave from an air burst reflects off the ground, which enhances its destructive power. A ground burst , in contrast, digs a huge crater and pulverizes everything in the immediate vicinity, but its blast effects don’t extend as far. Nuclear attacks on cities would probably employ air bursts, whereas ground bursts would be used on hardened military targets such as underground missile silos. As you’ll soon see, the two types of blasts have different implications for radioactive fallout.

How far do a weapon’s destructive effects extend? That distance — the radius of destruction — depends on the explosive yield. The volume encompassing a given level of destruction depends directly on the weapon’s yield. Because volume is proportional to the radius cubed, that means the destructive radius grows approximately as the cube root of the yield. A 10-fold increase in yield then increases the radius of destruction by a factor of only a little over two. The area of destruction grows faster but still not in direct proportion to the yield. That relatively slow increase in destruction with increasing yield is one reason why multiple smaller weapons are more effective than a single larger one. Twenty 50-kiloton warheads, for example, destroy nearly three times the area leveled by a numerically equivalent 1-megaton weapon.

What constitutes the radius of destruction also depends on the level of destruction you want to achieve. Roughly speaking, though, the distance at which overpressure has fallen to about 5 psi is a good definition of destructive radius. Many of the people within this distance would be killed, although some wouldn’t. But some would be killed beyond the 5-psi distance, making the situation roughly equivalent to having everyone within the 5-psi circle killed and everyone outside surviving. The image to the left shows how the destructive zone varies with explosive yield for a hypothetical explosion. This is a simplified picture; a more careful calculation of the effects of nuclear weapons on entire populations requires detailed simulations that include many environmental and geographic variables.

The blast wave is over in a minute or so, but the immediate destruction may not be. Fires started by the thermal flash or by blast effects still rage, and under some circumstances they may coalesce into a single gigantic blaze called a firestorm that can develop its own winds and thus cause the fire to spread. Hot gases rise from the firestorm, replaced by air rushing inward along the surface at hundreds of miles per hour. Winds and fire compound the blast damage, and the fire consumes enough oxygen to suffocate any remaining survivors.

During World War II, bombing of Hamburg with incendiary chemicals resulted in a firestorm that claimed 45,000 lives. The nuclear bombing of Hiroshima resulted in a firestorm; that of Nagasaki did not, likely because of Nagasaki’s rougher terrain. The question of firestorms is important not only to the residents of a target area: Firestorms might also have significant long-term effects on the global climate, as we’ll discuss later.

Both nuclear and conventional weapons produce destructive blast effects, although of vastly different magnitudes. But radioactive fallout is unique to nuclear weapons. Fallout consists primarily of fission products, although neutron capture and other nuclear reactions contribute additional radioactive material. The term fallout generally applies to those isotopes whose half-lives exceed the time scale of the blast and other short-term effects. Although fallout contamination may linger for years and even decades, the dominant lethal effects last from days to weeks, and contemporary civil defense recommendations are for survivors to stay inside for at least 48 hours while the radiation decreases.

The fallout produced in a nuclear explosion depends greatly on the type of weapon, its explosive yield, and where it’s exploded. The neutron bomb, although it produces intense direct radiation, is primarily a fusion device and generates only slight fallout from its fission trigger. Small fission weapons like those used at Hiroshima and Nagasaki produce locally significant fallout. But the fission-fusion-fission design used in today’s thermonuclear weapons introduces the new phenomenon of global fallout . Most of this fallout comes from fission of the U-238 jacket that surrounds the fusion fuel. The global effect of these huge weapons comes partly from the sheer quantity of radioactive material and partly from the fact that the radioactive cloud rises well into the stratosphere, where it may take months or even years to reach the ground. Even though we’ve had no nuclear war since the bombings of Hiroshima and Nagasaki, fallout is one weapons effect with which we have experience. Atmospheric nuclear testing before the 1963 Partial Test Ban Treaty resulted in detectable levels of radioactive fission products across the globe, and some of that radiation is still with us.

Fallout differs greatly depending on whether a weapon is exploded at ground level or high in the atmosphere. In an air burst, the fireball never touches the ground, and radioactivity rises into the stratosphere. This reduces local fallout but enhances global fallout. In a ground burst, the explosion digs a huge crater and entrains tons of soil, rock, and other pulverized material into its rising cloud. Radioactive materials cling to these heavier particles, which drop back the ground in a relatively short time. Rain may wash down particularly large amounts of radioactive material, producing local hot spots of especially intense radioactivity. A hot spot in Albany, New York, thousands of miles from the 1953 Nevada test that produced it, exposed area residents to some 10 times their annual background radiation dose. The exact distribution of fallout depends crucially on wind speed and direction; under some conditions, lethal fallout may extend several hundred miles downwind of an explosion. However, it’s important to recognize that the lethality of fallout quickly decreases as short-lived isotopes decay.

Recommended Response to a Nuclear Explosion

The United States government has recently provided guidance on how to respond to a nuclear detonation. One recommendation is to divide the region of destruction due to blast effects into three separate damage zones. This division provides guidance for first responders in assessing the situation. Outermost is the light damage zone , characterized by “broken windows and easily managed injuries.” Next is the moderate damage zone with “significant building damage, rubble, downed utility lines and some downed poles, overturned automobiles, fires, and serious injuries.” Finally, there’s the severe damage zone , where buildings will be completely collapsed, radiation levels high, and survivors unlikely.

The recommendations also define a dangerous fallout zone spanning different structural damage zones. This is the region where dose rates exceed a whole-body external dose of about 0.1 Sv/hour. First responders must exercise special precautions as they approach the fallout zone in order to limit their own radiation exposure. The dangerous fallout zone can easily stretch 10 to 20 miles (15 to 30 kilometers) from the detonation depending on explosive yield and weather conditions.

Electromagnetic Pulse

A nuclear weapon exploded at very high altitude produces none of the blast or local fallout effects we’ve just described. But intense gamma rays knock electrons out of atoms in the surrounding air, and when the explosion takes place in the rarefied air at high altitude this effect may extend hundreds of miles. As they gyrate in Earth’s magnetic field, the electrons generate an intense pulse of radio waves known as an electromagnetic pulse (EMP).

A single large weapon exploded some 200 miles over the central United States could blanket the entire country with an electromagnetic pulse intense enough to damage computers, communication systems, and other electronic devices. It could also affect satellites used for military communications, reconnaissance, and attack warning. The EMP phenomenon thus has profound implications for a military that depends on sophisticated electronics. In 1962, the United States detonated a 1.4-megaton warhead 250 miles above Johnston Island in the Pacific Ocean. People as far as Australia and New Zealand witnessed the explosion as a red aurora appearing in the night sky. Hawaiians, only 800 miles from the island, experienced a bright flash followed by a green sky and the failure of hundreds of street lights. In total, the Soviet Union and the United States conducted 20 tests of EMP from nuclear detonations. However, it’s unclear how to extrapolate the results to today’s more sensitive and more pervasive electronic equipment.

Since the Partial Test Ban Treaty of 1963 it has been virtually impossible to study EMP effects directly, although elaborate devices have been developed to mimic the electronic impact of nuclear weapons. Increasingly, crucial electronic systems are “hardened” to minimize the impact of EMP. Nevertheless, the use of EMP in a war could wreak havoc with systems for communication and control of military forces.

Many countries are around the world are developing high-powered microwave weapons which, although not nuclear devices, are designed to produce EMPs. These directed-energy weapons , also called e-bombs , emit large pulses of microwaves to destroy electronics on missiles, to stop cars, to detonate explosives remotely, and to down swarms of drones. Despite these EMP weapons being nonlethal in the sense that there’s no bang or blast wave, an enemy may be unable to distinguish their effects from those of nuclear weapons.

Would the high-altitude detonation of a nuclear weapon to produce EMP or the use of a directed-beam EMP weapon be an act of war warranting nuclear retaliation? With its electronic warning systems in disarray, should the EMPed nation launch a nuclear strike on the chance that it was about to be attacked? How are nuclear decisions to be made in a climate of EMP-crippled communications? These are difficult questions, but military strategists need to have answers.

Nuclear War

So far we’ve examined the effects of single nuclear explosions. But a nuclear war would involve hundreds to thousands of explosions, creating a situation for which we simply have no relevant experience. Despite decades of arms reduction treaties, there are still thousands of nuclear weapons in the world’s arsenals. Detonating only a tiny fraction of these would cause mass casualties.

What would a nuclear war be like? When you think of nuclear war, you probably envision an all-out holocaust in which adversaries unleash their arsenals in an attempt to inflict the most damage. Many people — including your authors — believe that misfortune to be the likely outcome of almost any use of nuclear weapons among the superpowers. But nuclear strategists have explored many scenarios that fall short of the all-out nuclear exchange. What might these limited nuclear wars be like? Could they really remain limited ?

Limited Nuclear War

One form of limited nuclear war would be like a conventional battlefield conflict but using low-yield tactical nuclear weapons. Here’s a hypothetical scenario: After its 2014 annexation of Crimea, Russia attacks a Baltic country with tanks and ground forces while the United States is distracted by a domestic crisis. NATO responds with decisive counterforce, destroying Russian tanks with fighter jets, but this doesn’t quell Russian resolve. Russia responds with even more tanks and by bombing NATO installations, killing several hundred troops. NATO cannot tolerate such aggression and to prevent further Russian advance launches low-yield tactical nuclear weapons with their dial-a-yield positions set to the lowest settings of only 300 tons TNT equivalent. The goal is to signal Russia that it has crossed a line and to deescalate the situation. NATO’s actions are based on fear that if the Russian aggression weren’t stopped the result would be all-out war in northern Europe.

This strategy is actually being discussed in the higher echelons of the Pentagon. The catchy concept is that use of a few low-yield nuclear weapons could show resolve, with the hoped-for outcome that the other party will back down from its aggressive behavior (this concept is known as escalate to deescalate ). The assumption is that the nuclear attack would remain limited, that parties would go back to the negotiating table, and that saner voices would prevail. However, this assumes a chain of events where everything unfolds as expected. It neglects the incontrovertible fact that, as the Prussian general Carl von Clausewitz observed in the 19th century, “Three quarters of the factors on which action in war is based are wrapped in a fog of greater or lesser uncertainty.” Often coined fog of war , this describes the lack of clarity in wartime situations on which decisions must nevertheless be based. In the scenario described, sensors could have been damaged or lines of communication severed that would have reported the low-yield nature of the nuclear weapons. As a result, Russia might feel its homeland threatened and respond with an all-out attack using strategic nuclear weapons, resulting in millions of deaths.

There is every reason to believe that a limited nuclear war wouldn’t remain limited.

There is every reason to believe that a limited nuclear war wouldn’t remain limited. A 1983 war game known as Proud Prophet involved top-secret nuclear war plans and had as participants high-level decision makers including President Reagan’s Secretary of Defense Caspar Weinberger. The war game followed actual plans but unexpectedly ended in total nuclear annihilation with more than half a billion fatalities in the initial onslaught — not including subsequent deaths from starvation. The exercise revealed that a limited nuclear strike may not achieve the desired results! In this case, that was because the team playing the Soviet Union responded to a limited U.S. nuclear strike with a massive all-out nuclear attack.

What about an attack on North Korea? In 2017, some in the U.S. cabinet advocated for a “bloody nose” strategy in dealing with North Korea’s flagrant violations of international law. This is the notion that in response to a threatening action by North Korea, the U.S. would destroy a significant site to “bloody Pyongyang’s nose.” This might employ a low-yield nuclear attack or a conventional attack. The “bloody nose” strategy relies on the expectation that Pyongyang would be so overwhelmed by U.S. might that they would immediately back down and not retaliate. However, North Korea might see any type of aggression as an attack aimed at overthrowing their regime, and could retaliate with an all-or-nothing response using weapons of mass destruction (including but not necessarily limited to nuclear weapons) as well as their vast conventional force.

In September 2017, during the height of verbal exchanges between President Trump and the North Korean dictator Kim Jong-un, the U.S. flew B-1B Lancer bombers along the North Korean coast, further north of the demilitarized zone than the U.S. had ever done, while still staying over international waters. However, North Korea didn’t respond at all, making analysts wonder whether the bombers were even detected. Uncertainty in North Korea’s ability to discriminate different weapon systems might exacerbate a situation like this one and could lead the North Koreans viewing any intrusion as an “attack on their nation, their way of life and their honor.” This is exactly how the Soviet team in the Proud Prophet war game interpreted it.

What about a limited attack on the United States? Suppose a nuclear adversary decided to cripple the U.S. nuclear retaliatory forces (a virtual impossibility, given nuclear missile submarines, but a scenario considered with deadly seriousness by nuclear planners). Many of the 48 contiguous states have at least one target — a nuclear bomber base, a submarine support base, or intercontinental missile silos — that would warrant destruction in such an attack. The attack, which would require only a tiny fraction of the strategic nuclear weapons in the Russian arsenal, could kill millions of civilians. Those living near targeted bomber and submarine bases would suffer blast and local radiation effects. Intense fallout from ground-burst explosions on missile silos in the Midwest would extend all the way to the Atlantic coast. Fallout would also contaminate a significant fraction of U.S. cropland for up to year and would kill livestock. On the other hand, the U.S. industrial base would remain relatively unscathed, if no further hostilities occurred.

In contrast to attacking military targets, an adversary might seek to cripple the U.S. economy by destroying a vital industry. In one hypothetical attack considered by the congressional Office of Technology Assessment, ten Soviet SS-18 missiles, each with eight 1-megaton warheads, attack United States’ oil refineries. The result is destruction of two-thirds of the U.S. oil-refining capability. And even with some evacuation of major cities in the hypothetical crisis leading to the attack, 5 million Americans are killed.

Each of these “limited” nuclear attack scenarios kills millions of Americans — many, many times the 1.2 million killed in all the wars in our nation’s history. Do we want to entertain limited nuclear war as a realistic possibility? Do we believe nuclear war could be limited to “only” a few million casualties? Do we trust the professional strategic planners who prepare our possible nuclear responses to an adversary’s threats? What level of nuclear preparedness do we need to deter attack?

All-Out Nuclear War

Whether from escalation of a limited nuclear conflict or as an outright full-scale attack, an all-out nuclear war remains possible as long as nuclear nations have hundreds to thousands of weapons aimed at one another. What would be the consequences of all-out nuclear war?

Within individual target cities, conditions described earlier for single explosions would prevail. (Most cities, though, would likely be targeted with multiple weapons.) Government estimates suggest that over half of the United States’ population could be killed by the prompt effects of an all-out nuclear war. For those within the appropriate radii of destruction, it would make little difference whether theirs was an isolated explosion or part of a war. But for the survivors in the less damaged areas, the difference could be dramatic.

Consider the injured. Thermal flash burns extend well beyond the 5-psi radius of destruction. A single nuclear explosion might produce 10,000 cases of severe burns requiring specialized medical treatment; in an all-out war there could be several million such cases. Yet the United States has facilities to treat fewer than 2,000 burn cases — virtually all of them in urban areas that would be leveled by nuclear blasts. Burn victims who might be saved, had their injuries resulted from some isolated cause, would succumb in the aftermath of nuclear war. The same goes for fractures, lacerations, missing limbs, crushed skulls, punctured lungs, and myriad other injuries suffered as a result of nuclear blast. Where would be the doctors, the hospitals, the medicines, the equipment needed for their treatment? Most would lie in ruin, and those that remained would be inadequate to the overwhelming numbers of injured. Again, many would die whom modern medicine could normally save.

A single nuclear explosion might produce 10,000 cases of severe burns requiring specialized medical treatment; in an all-out war there could be several million such cases.

In an all-out war, lethal fallout would cover much of the United States. Survivors could avoid fatal radiation exposure only when sheltered with adequate food, water, and medical supplies. Even then, millions would be exposed to radiation high enough to cause lowered disease resistance and greater incidence of subsequent fatal cancer. Lowered disease resistance could lead to death from everyday infections in a population deprived of adequate medical facilities. And the spread of diseases from contaminated water supplies, nonexistent sanitary facilities, lack of medicines, and the millions of dead could reach epidemic proportions. Small wonder that the international group Physicians for Social Responsibility has called nuclear war “the last epidemic.”

Attempts to contain damage to cities, suburbs, and industries would suffer analogously to the treatment of injured people. Firefighting equipment, water supplies, electric power, heavy equipment, fuel supplies, and emergency communications would be gone. Transportation into and out of stricken cities would be blocked by debris. The scarcity of radiation-monitoring equipment and of personnel trained to operate it would make it difficult to know where emergency crews could safely work. Most of all, there would be no healthy neighboring cities to call on for help; all would be crippled in an all-out war.

Is Nuclear War Survivable?

We’ve noted that more than half the United States’ population might be killed outright in an all-out nuclear war. What about the survivors?

Recent studies have used detailed three-dimensional, block-by-block urban terrain models to study the effects of 10-kiloton detonations on Washington, D.C. and Los Angeles. The results settle an earlier controversy about whether survivors should evacuate or shelter in place: Staying indoors for 48 hours after a nuclear blast is now recommended. That time allows fallout levels to decay by a factor of 100. Furthermore, buildings between a survivor and the blast can block the worst of the fallout, and going deep inside an urban building can lower fallout levels still further. The same shelter-in-place arguments apply to survivors in the non-urban areas blanketed by fallout.

These new studies, however, consider only single detonations as might occur in a terrorist or rogue attack. In considering all-out nuclear war, we have to ask a further question: Then what?

Individuals might survive for a while, but what about longer term, and what about society as a whole? Extreme and cooperative efforts would be needed for long-term survival, but would the shocked and weakened survivors be up to those efforts? How would individuals react to watching their loved ones die of radiation sickness or untreated injuries? Would an “everyone for themselves” attitude prevail, preventing the cooperation necessary to rebuild society? How would residents of undamaged rural areas react to the streams of urban refugees flooding their communities? What governmental structures could function in the postwar climate? How could people know what was happening throughout the country? Would international organizations be able to cope?

Staying indoors for 48 hours after a nuclear blast is now recommended. That time allows fallout levels to decay by a factor of 100.

Some students of nuclear war see postwar society in a race against time. An all-out war would have destroyed much of the nation’s productive capacity and would have killed many of the experts who could help guide social and physical reconstruction. The war also would have destroyed stocks of food and other materials needed for survival.

On the other hand, the remaining supplies would have to support only the much smaller postwar population. The challenge to the survivors would be to establish production of food and other necessities before the supplies left from before the war were exhausted. Could the war-shocked survivors, their social and governmental structure shattered, meet that challenge? That is a very big nuclear question — so big that it’s best left unanswered, since only an all-out nuclear war could decide it definitively.

Climatic Effects

A large-scale nuclear war would pump huge quantities of chemicals and dust into the upper atmosphere. Humanity was well into the nuclear age before scientists took a good look at the possible consequences of this. What they found was not reassuring.

The upper atmosphere includes a layer enhanced in ozone gas, an unusual form of oxygen that vigorously absorbs the Sun’s ultraviolet radiation. In the absence of this ozone layer , more ultraviolet radiation would reach Earth’s surface, with a variety of harmful effects. A nuclear war would produce huge quantities of ozone-consuming chemicals, and studies suggest that even a modest nuclear exchange would result in unprecedented increases in ultraviolet exposure. Marine life might be damaged by the increased ultraviolet radiation, and humans could receive blistering sunburns. More UV radiation would also lead to a greater incidence of fatal skin cancers and to general weakening of the human immune system.

Even more alarming is the fact that soot from the fires of burning cities after a nuclear exchange would be injected high into the atmosphere. A 1983 study by Richard Turco, Carl Sagan, and others (the so-called TTAPS paper) shocked the world with the suggestion that even a modest nuclear exchange — as few as 100 warheads — could trigger drastic global cooling as airborne soot blocked incoming sunlight. In its most extreme form, this nuclear winter hypothesis raised the possibility of extinction of the human species. (This is not the first dust-induced extinction pondered by science. Current thinking holds that the dinosaurs went extinct as a result of climate change brought about by atmospheric dust from an asteroid impact; indeed, that hypothesis helped prompt the nuclear winter research.)

The original nuclear winter study used a computer model that was unsophisticated compared to present-day climate models, and it spurred vigorous controversy among atmospheric scientists. Although not the primary researcher on the publication, Sagan lent his name in order to publicize the work. Two months before Science would publish the paper, he decided to introduce the results in the popular press. This backfired, as Sagan was derided by hawkish physicists like Edward Teller who had a stake in perpetuating the myth that nuclear war could be won and the belief that a missile defense system could protect the United States from nuclear attack. Teller called Sagan an “excellent propagandist” and suggested that the concept of nuclear winter was “highly speculative.” The damage was done, and many considered the nuclear winter phenomenon discredited.

But research on nuclear winter continued. Recent studies with modern climate models show that an all-out nuclear war between the United States and Russia, even with today’s reduced arsenals, could put over 150 million tons of smoke and soot into the upper atmosphere. That’s roughly the equivalent of all the garbage the U.S. produces in a year! The result would be a drop in global temperature of some 8°C (more than the difference between today’s temperature and the depths of the last ice age), and even after a decade the temperature would have recovered only 4°C. In the world’s “breadbasket” agricultural regions, the temperature could remain below freezing for a year or more, and precipitation would drop by 90 percent. The effect on the world’s food supply would be devastating.

Even a much smaller nuclear exchange could have catastrophic climate consequences. The research cited above also suggests that a nuclear exchange between India and Pakistan, involving 100 Hiroshima-sized weapons, would shorten growing seasons and threaten annual monsoon rains, jeopardizing the food supply of a billion people. The image below shows the global picture one month after this hypothetical 100-warhead nuclear exchange.

Nuclear weapons have devastating effects. Destructive blast effects extend miles from the detonation point of a typical nuclear weapon, and lethal fallout may blanket communities hundreds of miles downwind of a single nuclear explosion. An all-out nuclear war would leave survivors with few means of recovery, and could lead to a total breakdown of society. Fallout from an all-out war would expose most of the belligerent nations’ surviving populations to radiation levels ranging from harmful to fatal. And the effects of nuclear war would extend well beyond the warring nations, possibly including climate change severe enough to threaten much of the planet’s human population.

Debate about national and global effects of nuclear war continues, and the issues are unlikely to be decided conclusively without the unfortunate experiment of an actual nuclear war. But enough is known about nuclear war’s possible effects that there is near universal agreement on the need to avoid them. As the great science communicator and astronomer Carl Sagan once said, “It’s elementary planetary hygiene to clean the world of these nuclear weapons.” But can we eliminate nuclear weapons? Should we? What risks might such elimination entail? Those are the real issues in the ongoing debates about the future of nuclear weaponry.

Richard Wolfson is Benjamin F. Wissler Professor of Physics at Middlebury College. Ferenc Dalnoki-Veress is Scientist-in-Residence at the Center for Nonproliferation Studies of the Middlebury Institute of International Studies. This article is excerpted from their book “ Nuclear Choices for the Twenty-First Century: A Citizen’s Guide. “

air burst A nuclear explosion detonated at an altitude—typically, thousands of feet—that maximizes blast damage. Because its fireball never touches the ground, an air burst produces less radioactive fallout than a ground burst.

blast wave An abrupt jump in air pressure that propagates outward from a nuclear explosion, damaging or destroying whatever it encounters.

direct radiation Nuclear radiation produced in the actual detonation of a nuclear weapon and constituting the most immediate effect on the surrounding environment.

electromagnetic pulse (EMP) An intense burst of radio waves produced by a high-altitude nuclear explosion, capable of damaging electronic equipment over thousands of miles.

fallout Radioactive material, mostly fission products, released into the environment by nuclear explosions.

fireball A mass of air surrounding a nuclear explosion and heated to luminous temperatures.

firestorm A massive fire formed by coalescence of numerous smaller fires.

ground burst A nuclear explosion detonated at ground level, producing a crater and significant fallout but less widespread damage than an air burst.

nuclear difference Phrase we use to describe the roughly million-fold difference in energy released in nuclear reactions versus chemical reactions.

nuclear winter A substantial reduction in global temperature that might result from soot injected into the atmosphere during a nuclear war.

overpressure Excess air pressure encountered in the blast wave of a nuclear explosion. Overpressure of a few pounds per square inch is sufficient to destroy typical wooden houses.

radius of destruction The distance from a nuclear blast within which destruction is near total, often taken as the zone of 5-pound-per-square-inch overpressure.

thermal flash An intense burst of heat radiation in the seconds following a nuclear explosion. The thermal flash of a large weapon can ignite fires and cause third-degree burns tens of miles from the explosion.

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National Research Council (US); National Academy of Sciences (US); Neel JV, Schull WJ, editors. The Children of Atomic Bomb Survivors: A Genetic Study. Washington (DC): National Academies Press (US); 1991.

The Children of Atomic Bomb Survivors: A Genetic Study.

• Hardcopy Version at National Academies Press

Genetic Effects of the Atomic Bombs in Hiroshima and Nagasaki

Genetics Conference, Committee on Atomic Casualties, National Research Council

The Atomic Energy Commission recently formally signified its intention of supporting long-range medical studies of the survivors of the atomic bombings in Japan, to be conducted by the Committee on Atomic Casualties of the National Research Council. One aspect of these studies will concern the much-discussed potential genetic effects of the bombs. The background of this program begins shortly after Japan's surrender, when a Joint Army-Navy Commission made extensive observations in Hiroshima and Nagasaki on the survivors of the bombings. At the conclusion of the Commission's work its chairman, Col. A.W.Oughterson, M.C., AUS, recommended to the Surgeon General of the Army that the Council be requested to undertake a long-range study of the medical and biological effects of the atomic bomb, and this recommendation was transmitted by Surgeon Gen. Norman T.Kirk to Lewis H.Weed, chairman of the Division of Medical Sciences. As a result, in June 1946 a conference group was convened by the Council, and in November, following its recommendation, a five-man commission composed of representatives of the Council, the Army, and the Navy left for Japan for the purpose of determining the current status of Japanese work on atomic bomb casualties, evaluating the feasibility of American participation in continued research on these casualties, and indicating the lines along which such studies should proceed. This commission, known as the Atomic Bomb Casualty Commission and composed of Austin Brues, Paul S.Henshaw, Lt. Melvin Block, M.C., AUS, Lt. James V.Neel, M.C., AUS, and Lt. (j.g.) Frederick Ullrich, (MC) USNR, submitted a report of its findings to the Council in January 1947.

The June 1946 conference group had recommended that appropriate action be taken to obtain a Presidential Directive authorizing the National Research Council to initiate a long range study of the atomic bomb effects. This Directive was issued at the request of the Secretary of the Navy, James T. Forrestal, in November 1946, and on its authority the Council, in January 1947, established a Committee on Atomic Casualties, composed of Thomas M.Rivers (chairman), George W. Beadle, Detlev W.Bronk, Austin Brues, George M.Lyon, C.P.Rhoads, Shields Warren, Stafford L.Warren, George H.Whipple, and Raymond E.Zirkle.

The potential genetic effects of the atomic bomb were apparent to all interested students from the day the first bomb was dropped—in fact, to some, well before that time. A consideration of genetic studies was one facet of the work of the Atomic Bomb Casualty Commission, and a section of its January 1947 report was devoted to this subject. This phase of the work was to a large extent the responsibility of Lt. James V.Neel.

On June 24, 1947, the Committee on Atomic Casualties arranged a conference on the potential genetic effects of the atomic bombs. At this meeting, which was attended by George W.Beadle (chairman), Donald R.Charles, Charles H.Danforth, Herman J.Muller, Laurence H.Snyder, and Lt. Neel, the latter submitted a report of preliminary genetic studies, based on his observations in Japan during the preceding six months. Following a thorough appraisal of the problem, the conference voted to recommend to the Committee on Atomic Casualties that a program be undertaken in Japan along the lines sketched out in the Neel report. This recommendation was accepted at a meeting of the Committee on June 26, 1947. The conference also recommended that a statement be prepared, briefly summarizing the current status of the problem. This statement follows.

WHETHER THE ATOMIC BOMBS dropped on Hiroshima and Nagasaki will have detectable genetic effects on the Japanese is a question of widespread interest. The purpose of the present note is to show briefly that (1) many difficulties beset any attempt to obtain a valid answer to this question and (2) even after a long-term study, such as that outlined below, it still may not be possible to determine just how much genetic damage was done at Hiroshima and Nagasaki.

This memorandum is essentially a partial summary of the material presented by Lt. James V.Neel at the meeting of the Conference on Genetics convened by the Committee on Atomic Casualties of the National Research Council on June 24, 1947, but with certain additional considerations which grew out of the deliberations of the Conference.

It must first be recognized that, inasmuch as the majority of mutations occurring in animals are recessive, only the relatively small proportion of mutations which are dominants may be expected to show effects in the first postbomb generation. The potential range in their effects is very wide. Dominant mutations with large, clear-cut manifestations can be expected to be much rarer than those with smaller, but possibly quite significant, effects on bodily dimensions, life span, etc. But the detection of these latter is a matter of great difficulty with present techniques. For practical considerations investigation will have to be concentrated chiefly on the class with such large effects as may lead to stillbirths, to live births with gross external abnormality, or to internal defects causing death or serious illness in infancy.

Since there is no general agreement as to what proportion of cases of abnormal fetal development is genetically determined, and what proportion is due to nongenetic factors, an increased incidence of morphologically abnormal fetuses following irradiation may not be used as an index of the frequency of genetic change until the non- genetic effects of this irradiation on the reproductive history of the mother have been determined. This point will be very difficult to evaluate.

It is obvious that in this case the approach to the problem of genetic effects is the statistical one. It is unlikely that any individual and specific pathology in a post-irradiation generation can ever be attributed with certainty to the effects of the bomb, but if there is a definite increase in the occurrence of abortions, miscarriages, stillbirths, and abnormal products of conception, one may surmise that this is related to the bombing—although some of the effects need not necessarily be genetic. Appropriate control studies in other Japanese cities are therefore of the utmost importance.

The survivors of the bombing received amounts of irradiation ranging from negligible to just short of lethal. It is impossible to say on a priori grounds whether an adequate number of people absorbed sufficient radiation to produce enough dominant mutations to result in detectable effects. However, comparison of this situation with the experimental data on infrahuman material suggests that these effects, if detectable, will be small. The median lethal dose for whole body irradiation in man is probably in the neighborhood of 500 Roentgen units (Shields Warren. Physiol. Rev., 1944, 24, 225–238). It is likely that many individuals in Hiroshima and Nagasaki who received high but sublethal doses of irradiation sustained other injuries which, in combination with the radiation damage, resulted in death. Thus, the mean radiation dose received by the surviving population will be lower than expected from a consideration of the median lethal dose alone. In terms of radiation genetics this is a small exposure, expected from data on animals to produce a frequency of dominant mutations which would increase the normal frequency of abnormal offspring by so small a proportion as to be difficult to demonstrate. Large-scale studies, utilizing all available material, plus accurate vital statistics, are thus necessary if data of value are to be obtained. In this connection it is important to bear in mind that the available children born to parents who received significant amounts of irradiation will probably not exceed 12,000 or 13,000 within the next 10 years.

The Japanese had recognized the importance of genetic studies and, under great difficulties, were organizing a program in Hiroshima when the Atomic Bomb Casualty Commission arrived. They had planned to compare the present and future frequency of abnormal births in Hiroshima with the frequencies reported in their medical literature and vital statistics during the prewar years. But it is by no means sure either that the prewar figures were sufficiently accurate or that the present reporting of vital statistics would be wholly effective in detecting rare effects of the atomic bomb radiations. It cannot be too strongly emphasized that there is at present absolutely no reliable evidence on which to base any opinion concerning the absolute or relative frequency of congenital abnormalities among children being born in Hiroshima and Nagasaki. Unfortunately, a good deal of misinformation is currently in circulation.

Two independent programs, one Japanese and one American, would involve needless duplication of effort. A joint undertaking is therefore indicated. In view of the fact that the Japanese are actively attempting to initiate genetic studies, it seems that any American efforts which may materialize should contemplate cooperation with the Japanese in an attempt to ensure an efficient and satisfactory program. The Neel report contains the following seven specific recommendations as to the organization of a program:

Organize, in Hiroshima, Nagasaki, and a control area or areas, a modified system of pregnancy registration, this to include the irradiation history of the parents.

Obtain as complete information as possible on the outcome of each registered pregnancy.

Follow up each report of an abnormal termination of pregnancy or a congenital malformation with detailed family studies.

Develop a system of checking on the completeness and accuracy of registration of births and deaths, such as requiring at intervals dual registration by both the family and the obstetrician or midwife.

Conduct these studies on a sufficiently large scale that the results will have statistical significance.

Integrate this program with a system of periodic examination of the offspring of irradiated persons and with careful death certification, so that genetic effects not apparent at birth but detected subsequently may be recorded. In particular, causes of infant mortality should be accurately recorded.

Place this program in competent Japanese hands, through the Japanese Government, with only enough American supervision and cooperation, including supplies, to facilitate a successful program.

This program must extend over a period of 10–20 years before a significant amount of data can be accumulated, and quite possibly an even longer period of study, extending to the second and subsequent generations, will be indicated.

Certain practical limitations of the program may be considered at this point. The most difficult problem will be to obtain the necessary completeness of reporting. This will require constant effort, a wide educational program, and frequent cross-checks. Congenital malformations occurring within Japanese families may sometimes not be reported. This is perhaps more likely to occur in Japan than in this country, because probably less than 10 per cent of Japanese births occur in hospitals as these are defined in the United States. To what extent stillbirths and malformations occurring outside a hospital will be recorded depends on the vigor with which the problem is pursued. It will be difficult to get evenly matched teams of investigators for bombed and control areas. Furthermore, once people living in Hiroshima and Nagasaki learn that stillbirths and malformations may possibly be attributed to the effects of the bomb, they will probably lose some of their reluctance to report such matters, whereas this will not be the case in a control area.

Japan is now a defeated and occupied country, under severe postwar stress, whose people have a very different psychology from our own. A program such as that under consideration will proceed much more slowly there than it would in this country.

In order to reduce the possibility that a negative result of the investigation on Japanese material be interpreted by the medical and lay public as meaning that important genetic effects were not produced, it is essential that a comparable effort be expended in experimentation on other mammalian material, in which genetic effects of different kinds can much more readily be brought to light. In this way it should be possible to throw light upon the proportion of the total genetic effects produced by the radiation that would have been detectable by the methods used in the investigation on the human material, and the serious danger of misinterpretation of the latter results would be minimized.

Recognizing the difficulties briefly touched upon in the foregoing paragraphs, the Conference on Genetics voted unanimously to record the following expression of its attitude toward the genetic program: “Although there is every reason to infer that genetic effects can be produced and have been produced in man by atomic radiation, nevertheless the conference wishes to make it clear that it cannot guarantee significant results from this or any other study on the Japanese material. In contrast to laboratory data, this material is too much influenced by extraneous variables and too little adapted to disclosing genetic effects. In spite of these facts, the conference feels that this unique possibility for demonstrating genetic effects caused by atomic radiation should not be lost.”

• Cite this Page National Research Council (US); National Academy of Sciences (US); Neel JV, Schull WJ, editors. The Children of Atomic Bomb Survivors: A Genetic Study. Washington (DC): National Academies Press (US); 1991. Genetic Effects of the Atomic Bombs in Hiroshima and Nagasaki.
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Hiroshima and Nagasaki hit by nuclear bombs in 1945, radiation dissipated

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The U.S. bombings that ended World War II didn’t mark the close of atomic warfare. They were just the beginning.

From 1945 to 2017, nuclear nations carried out more than 2,000 explosive tests in the atmosphere, underground and underwater, mostly in remote places.

Larger circles indicate places with many repeated tests.

Some of the atmospheric tests were magnitudes more powerful than the bombs dropped on Japan, sickening and displacing thousands.

Their descendants — who continue to endure physical, psychological, economic and cultural fallout — are living proof that nuclear weapons should never be tested again. If only today’s leaders would take heed.

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About an hour’s drive from the Las Vegas Strip, deep craters pockmark the desert sand for miles in every direction. It’s here, amid the sunbaked flats, that the United States conducted 928 nuclear tests during the Cold War above and below ground. The site is mostly quiet now, and has been since 1992, when Washington halted America’s testing program.

There are growing fears this could soon change. As tensions deepen in America’s relations with Russia and China, satellite images reveal all three nations are actively expanding their nuclear testing facilities , cutting roads and digging new tunnels at long-dormant proving grounds, including in Nevada.

None of these nations have conducted a full-scale nuclear test since the 1990s. Environmental and health concerns pushed them to move the practice underground in the middle of the last century, before abandoning testing altogether at the end of the Cold War.

Each government insists it will not be the one to reverse the freeze. Russia and China have said little about the recent flurry of construction at their testing sites, but the United States emphasizes it’s merely modernizing infrastructure for subcritical tests, or underground experiments that test components of a weapon but fall short of a nuclear chain reaction.

The possibility of resuming underground nuclear testing has long loomed over the post-Cold War world. But only now do those fears seem worryingly close to being realized amid the growing animosity among the world powers, the construction at testing grounds and the development of a new generation of nuclear weapons.

As this pressure mounts, some experts fear that the United States could act first. Ernest Moniz, a physicist who oversaw the nation’s nuclear complex as energy secretary under President Barack Obama, said there’s increasing interest from members of Congress, the military and U.S. weapons laboratories to begin full-scale explosive tests once again. “Among the major nuclear powers, if there is a resumption of testing, it will be by the United States first,” Mr. Moniz said in a recent interview.

This article is part of the Opinion series At the Brink , about the threat of nuclear weapons in an unstable world. Read the opening piece here .

The Trump administration privately discussed conducting an underground test in hopes of coercing Russia and China into arms control talks in 2020, and this week his former national security adviser offered a possible preview of Mr. Trump’s second term by publicly urging him to restart the nuclear testing program. The Biden administration is adamant that technological advances have made it unnecessary to resume full-scale testing, but in May it began the first in a series of subcritical tests to ensure America’s modern nuclear warheads would still work as designed. These experiments fall within the United States’ promise not to violate the testing taboo.

A return to that earlier era is certain to have costly consequences. The United States and the Soviet Union might have narrowly avoided mutual destruction, but there was a nuclear war: The blitz of testing left a wake of illness, displacement and destruction, often in remote locations where marginalized communities had no say over what happened on their own land. Millions of people living in those places — Semipalatinsk, Kazakhstan; Reggane, Algeria; Montebello, Australia; the Republic of Kiribati — became unwitting casualties to an arms race run by a handful of rich, powerful nations.

The United States detonated the first underwater nuclear weapon in the Bikini Atoll, Marshall Islands, in 1946.

Many nuclear experts believe that a single explosive test by any of the major nuclear powers could lead to a resumption of testing among them all. And while the world is unlikely to return to the Cold War spectacle of billowing mushroom clouds from tests in the earth’s atmosphere, even a resumption of underground testing, which still can emit hazardous radiation, could expose new generations to environmental and health risks.

It would open a volatile chapter in the new nuclear age as we’re still trying to understand the fallout from the first one.

The Republic of the Marshall Islands Embassy is a modest, red brick building in a leafy Washington, D.C., neighborhood. Inside, a room on the first floor is packed with cardboard boxes and filing cabinets, each brimming with U.S. government documents detailing America’s nuclear testing program in the islands. It seems like a generous collation of history — until you open a box, pick up a page and see the endless blocks of text blacked out mostly for what the government claims are national security reasons.

While the Nevada test site hosted more nuclear detonations than any other place on the planet, the United States tested its largest bombs at the Pacific Proving Grounds. The 67 nuclear weapons tested in the Marshalls from 1946 to 1958 involved blasts hundreds of times more powerful than the American bomb that demolished Hiroshima, Japan.

The potential health risks of testing were known from the start of the U.S. nuclear weapons program. Five days after J. Robert Oppenheimer’s team covertly detonated the first atomic bomb in New Mexico in July 1945, a U.S. government memorandum was drawn up describing “the dust outfall from the various portions of the cloud was potentially a very serious hazard” for people living downwind of the desert test site.

And so when World War II ended and the nation’s rush to fine-tune its new weapon began, Washington looked for a remote location to test the bomb. The search ultimately turned up two spots: One was a 680-square-mile stretch of desert northwest of Las Vegas, in the region where Dr. Oppenheimer made the bomb. The other was much farther from home, in the middle of the Pacific Ocean.

In February 1946, just six months after the United States dropped two atomic bombs on Japan, a Navy officer appeared in the Marshall Islands, a collection of more than 1,000 islands scattered across 750,000 square miles between Hawaii and the Philippines. The United States had taken control of the islands from Japan during the war, and the military identified Bikini Atoll, a coral reef where people had lived for thousands of years, as an ideal testing ground.

After a Sunday afternoon church service, Commodore Ben Wyatt, the American military governor of the islands, made a religious appeal to the Bikini leader King Juda and his people, asking if they were willing to sacrifice their island for the welfare of all men. In truth, they had no choice: Preparations were already underway on the order of President Harry Truman.

Not long after, 167 Bikinians were ushered aboard a relocation ship and sent over 100 miles away to an island with scant vegetation and a lagoon full of poisonous fish. As they drifted toward their new home, they could see rising flames as American soldiers burned the huts and outrigger boats they left behind. Four months later, the U.S. military detonated two atomic bombs on Bikini Atoll. Though they planned to return, the Marshallese would never be able to safely live there again.

Unlike Dr. Oppenheimer’s first highly secretive atomic test, these explosions in the Pacific served as public spectacles. The military brought along journalists, politicians and reportedly 18 tons of camera equipment and half of the world’s supply of motion picture film to record the events. The goal was to get attention — specifically, the Soviet Union’s attention — by spreading information and footage of these new wonder weapons.

The tests did more than that. They kicked off a generation of nuclear proliferation across the globe. One by one, each country with the money and the drive to compete started its own nuclear weapons program. And when they did, they took their cue from the United States and tested the devices in far-flung locations — and in many cases, their own territories. The Soviet Union tested its weapons in Kazakhstan. The French in Africa and Polynesia. China in Xinjiang. The British in Australia.

Britain conducted nuclear weapons tests and experiments in Australia from 1952 to 1963. Carcinogenic plutonium released during the program has been absorbed into the soil and food chain over decades.

Karina Lester, who lives in southern Australia, worries about the effects on the land and her children.

The nuclear powers might have been the most technologically advanced countries in the world, but in hindsight, it’s clear they had little idea of what they were doing, and the health of the local populations was an afterthought, if a thought at all.

As tests continued at a breakneck pace, American scientists grew increasingly worried about the dangers posed by the weapons’ fallout. Chief among their fears was how much radioactive isotopes like strontium-90, formed in nuclear detonations, were being swept away on winds and falling back to earth through rain far beyond the remote blast areas onto farms and dairies where they could enter the food chain. Strontium-90, which is structurally similar to calcium and attaches to bones and teeth after being ingested, is known to cause cancer.

In the early 1950s, the Atomic Energy Commission, the U.S. agency overseeing nuclear weapons at the time, stationed roughly 150 remote monitors at home and abroad to pick up signs of radiation. It also started a program to obtain “human samples” to test for strontium, according to a declassified transcript from a 1955 meeting. “If anybody knows how to do a good job of body snatching, they will really be serving their country,” said Willard F. Libby, an agency commissioner at the time. Over the next several years, the U.S. government gathered over 1,500 body parts from cadavers, many of them stillborn babies, from several countries without knowledge of the subject’s next of kin.

While the government pursued this science in the shadows, civilian studies were also underway. Teams at St. Louis University and the Washington University School of Dental Medicine collected around 320,000 baby teeth, mainly from the St. Louis area, that were donated by parents and guardians. They found that children born in 1963 had 50 times the level of strontium-90 in their teeth as children born in 1950. The initial results would later become the first major public study to raise the alarm on testing’s inherent risk to human health.

Even as this research was unfolding, the U.S. government pressed on with its testing in the Marshall Islands. On March 1, 1954, it conducted its largest test, code-named Castle Bravo. American weapon designers drastically underestimated the size of the weapon’s explosion by nearly threefold, a devastating miscalculation.

The device, which had 1,000 times the force of the bomb dropped on Hiroshima, was set off before dawn, sending a blinding flash across the sky for 250 miles or more above the Pacific. Three small islands were instantly vaporized. A mushroom cloud shot about 25 miles into the stratosphere, suctioning up 10 million tons of pulverized coral debris.

Within weeks, Marshallese living within 100 miles of the blast became weak and nauseated, developed weeping lesions and lost fistfuls of hair. The U.S. military evacuated more than 230 people to a U.S. Navy base on the nearby Kwajalein Atoll. Once they were there, men, women and children were interned at a camp and unwittingly enrolled in a secret U.S. government medical program called Project 4.1 .

The goal was to find out how radiation from weapons affects humans, something scientists couldn’t fully register inside a laboratory through animal experimentation. “While it is true that these people do not live, I would say, the way Westerners do — civilized people — it is nevertheless also true that these people are more like us than the mice,” said Merril Eisenbud, then the Atomic Energy Commission’s chief of health and safety, in a declassified transcript.

The aftermath was grim. The group suffered from widespread symptoms associated with acute radiation sickness. The rate of miscarriage and stillbirth among women exposed to the fallout was roughly twice that in unexposed women during the first four years after the Castle Bravo test. Babies were born with transparent skin and without bones — what the Marshallese midwives call jellyfish babies — and young children disproportionately developed thyroid abnormalities, including cancer, because of their size and metabolism.

Even with this kind of evidence in hand, science has reached only limited conclusions about how nuclear weapons testing affects individuals’ health. Researchers know that the last century’s atmospheric testing sent radioactive fallout across the world, affecting countless people. In the United States alone, a study by the Centers for Disease Control and Prevention found that every person in the continental United States who has been alive since 1951 has had some exposure to radioactive fallout from nuclear testing.

But startlingly little analysis or funding has gone into the long-term study of the descendants of people exposed to nuclear weapons radiation. Many descendants believe that their family’s exposure explains their own illnesses, but they are often left without the data to back up — or refute — their claims. It is difficult for medical experts to say definitively whether any individual’s cancer or illness is a direct result of radioactivity or something else, such as smoking or exposure to other harmful products throughout their lives. They can only say that radiation increases the risks. To many downwinders, as nuclear testing survivors are globally known, the dearth of information feels like further evidence of being sidelined by their respective governments.

What the existing studies do show is that where there have been nuclear tests, there have also been an unusually high number of people with health problems. In northeast Kazakhstan, where the last of 456 Soviet tests took place more than three decades ago, children near the test site have been born without limbs or developed cancer in higher numbers than normal . Studies of the exposed population show that elevated levels of serious illness persisted for two generations. Across French Polynesia — where France conducted nuclear tests over three decades — thyroid, blood and lung cancers have been prevalent.

Even today, descendants of nuclear test survivors fear passing illnesses onto future generations.

France tested nuclear weapons in French Polynesia from 1966 to 1996. Facing worldwide protests and an international trade boycott, it finally ended its testing program.

Hinamoeura Morgant-Cross, born in Tahiti, is the fourth generation in her family to develop cancer.

After Castle Bravo, the evidence was unmistakable: A single bomb blowing up on one side of the globe could touch everyone on the other. The fallout from the test did not harm only the Marshallese. It also sickened fishermen aboard a nearby Japanese fishing ship and stoked widespread fears of contamination in Japanese fish stocks, retraumatizing Japan less than a decade after American bombs killed an estimated 200,000 people in Hiroshima and Nagasaki. Within a month, traces of fallout stretched from Asia to Europe. The massive U.S. experiment became a global news story, and calls for a global testing moratorium began almost immediately.

At the time of the Castle Bravo test, all three nuclear nations — the United States, the Soviet Union and Britain — were actively testing their weapons above ground. Within 10 years, the three superpowers signed the 1963 Limited Test Ban Treaty, which officially confined them to testing underground. France continued atmospheric testing until 1974, and China continued until 1980.

In underground tests, the nuclear explosions took place inside a canister placed within a vertical hole drilled more than 1,000 feet into the earth. Miles of electrical cables connected to the canister relayed information on the blast to recording stations on the surface. While that process avoided widespread radioactive fallout, it could still contaminate groundwater and cause so-called venting incidents, in which radioactive debris leaked from below ground into the air.

As a result, in 1996, the world’s largest nuclear powers signed the Comprehensive Nuclear Test Ban Treaty, which banned all nuclear explosions above and below ground and established a global monitoring system to detect any tests that take place. India and Pakistan, which did not sign the treaty, both held underground tests in 1998, but only North Korea has conducted them since.

For years, test survivors across the world have fought for compensation for what these experiments cost them: their homes, their health, their culture and their community. Spurred by the inaction among world powers, many individuals from these communities are outspoken activists at the forefront of the global disarmament movement. They helped create the 2021 Treaty on the Prohibition of Nuclear Weapons, signed by 93 countries, which bans the possession, use and testing of nuclear weapons.

Despite this mobilization, there are only a handful of examples of nuclear weapon states compensating downwinders for exploding the world’s biggest bombs near their neighborhoods and ancestral homelands. France has acknowledged its “debt” to Polynesians over nuclear testing, and it created a commission in 2010 to evaluate nuclear testing victim compensation claims, but it has never apologized. Neither has Britain, nor has it established means of compensation.

The Marshallese have had slightly more success than others. While the United States has never issued an apology for displacing thousands of people and rendering parts of the nation uninhabitable, it paid the Marshallese $150 million in the 1980s for what the U.S. government calls “a full and final” settlement of all claims related to the testing program. Since then, it has allocated hundreds of millions of dollars for education, health care, the environment and infrastructure, according to the U.S. government .

But it’s not enough. The Marshallese government has claimed roughly $3 billion in uncompensated damages.

As part of a 1986 compact, the United States gave control of the islands back to the Marshallese, while the U.S. military kept control of a sprawling missile-test site on Kwajalein Atoll. The compact also gave all Marshallese permission to live and work in the United States indefinitely without visas.

The deal has been a welcome development for the growing number of Marshallese who have simply given up on building a life back home, where unemployment and poverty remain pervasive, and good schools and quality health care are scarce. Small Marshallese communities are now scattered across the United States, including in Hawaii, California, Washington and Oregon. But the largest population of Marshallese in the world outside the islands is in a rural area surrounding the northwest corner of Arkansas, mainly in a small city called Springdale. So many Marshallese live in this agricultural industrial heartland — about 20,000 by one count — they call it the Springdale Atoll.

It began in the 1980s when a Marshallese man named John Moody landed a job in one of the area’s sprawling poultry plants. Soon more people started to arrive from the islands as news spread about the jobs, better doctors and schools. Today, when you’re in Springdale, it doesn’t take long to spot signs of the community: the Blue Pacific Mart convenience store, the KMRW 98.9 Marshallese radio station and dozens of homespun Marshallese churches.

Off Emma Avenue, the city’s main street, in a single-story, L-shaped building, Benetick Kabua Maddison runs the Marshallese Educational Initiative. Mr. Maddison, 29, took over the nonprofit in 2022 to raise awareness about the islands’ culture and nuclear testing legacy. His team teaches community members how the tests drove so many people to leave the islands and how the testing program affected their health.

The populations of entire islands were permanently displaced when America decided to test its weapons on the Marshall Islands, which it controlled after World War II. The tests left some of the islands, including Bikini Atoll, uninhabitable.

Benetick Kabua Maddison’s family was among them. He now lives in Arkansas.

Diabetes rates among the Marshallese globally are now 400 percent as high as for the general U.S. population. When Covid-19 came to Springdale in 2020, it hit the Marshallese community — like other groups across the states with high rates of noncommunicable diseases — disproportionately hard. Estimated to represent about 2 percent of the local population in northwest Arkansas, the Marshallese accounted for 38 percent of the deaths there during the pandemic’s first four months.

It was a stark reminder of nuclear testing’s complex and far-reaching legacy. “The Marshallese are living proof that nuclear weapons must never be used or tested again,” Mr. Maddison said.

Few places on earth can still convey the raw power of nuclear weapons like the Nevada Test Site. From a wooden observation platform, you can look out over a crater 320 feet deep and a quarter-mile wide created by a 104-kiloton device detonated underground in July 1962. It’s just one of the many man-made pits dotting the 1,375-square-mile proving grounds that are roughly the size of Rhode Island.

Today a sprawling tunnel network under the site, originally excavated in the 1960s for an underground nuclear test, is being transformed into a subterranean research laboratory to host the subcritical nuclear experiments that started again in May. American scientists hope the roughly $2.5 billion investment in new diagnostic, monitoring and computing equipment will help them gain further insights into exactly what happens inside a thermonuclear explosion, beyond what was learned from the live-fire tests that ended in the 1990s.

Knowing the increased activity will raise eyebrows, the Biden administration has publicly floated a plan to Russia and China to install radiation detection equipment near one another’s subcritical experiments to ensure an atomic chain reaction does not occur. A senior administration official says the United States is even considering inviting international observers or livestreaming the experiments to head off any skepticism of their intentions.

Mistrust is already running deep. While all nuclear nations that signed the Comprehensive Nuclear Test Ban Treaty have appeared to observe it in practice, both China and the United States failed to ratify the treaty because of internal political challenges — and the desire to keep their options for future testing open without running afoul of international law.

In November, Russia rescinded its ratification, citing the United States’ failure to ratify the pact. President Vladimir Putin intimated that if Washington tested again, Moscow would follow with one of its own. He took another step in that direction on June 7, saying that Russia could test a nuclear weapon but that there was no need at the present time.

For now in Nevada, roughly 1,000 feet above the underground lab, remnants from the last nuclear era — cables, containers and equipment — sit idle in a fenced-off area atop the desert flats. They are still stored on-site and on standby, upon government mandate, to be ready for use should a president ever issue the order for explosive testing to begin once again.

The world can’t afford to restart this dangerous cycle. We are still wrestling with the damage wrought by testing nuclear weapons in our past. It shouldn’t be a part of our future.

W.J. Hennigan writes about national security issues for Opinion from Washington, D.C. He has reported from more than two dozen countries, covering war, the arms trade and the lives of U.S. service members. Additional reporting by Spencer Cohen.

Photographs by Ike Edeani. Top grid of testing survivors and descendants: Tamatoa Tepuhiarii, Aigerim Yelgeldy, Adiya Akhmer, Raygon Jacklick, Benetick Kabua Maddison, Karina Lester, Hinamoeura Morgant-Cross, Kairo Langrus, Aigerim Seitenova, Ereti Tekabaia, Matthew John and Mere Tuilau. Tamatoa Tepuhiarii, Adiya Akhmer, Raygon Jacklick, Benetick Kabua Maddison, Hinamoeura Morgant-Cross, Aigerim Yelgeldy, Aigerim Seitenova, Matthew John, Kairo Langrus, Karina Lester, Ereti Tekabaia and Mere Tuilau

Video produced by Amanda Su, Elliot deBruyn and Jonah M. Kessel. Archival videos: Établissement de communication et de production audiovisuelle de la Défense, Grinberg, Paramount, Pathe Newsreels, The Associated Press, Getty Images.

Graphics by Gus Wezerek. Testing locations for the map from Reuters and the Stockholm International Peace Research Institute.

This Times Opinion series is funded through philanthropic grants from the Carnegie Corporation of New York , Outrider Foundation and the Prospect Hill Foundation . Funders have no control over the selection or focus of articles or the editing process and do not review articles before publication. The Times retains full editorial control.

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Is there a minimum size for an atomic bomb?

19 June 2024

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Is there a minimum size for an atomic bomb? Would it be possible to make a microscopic one that results in a very small explosion?

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Nuclear explosions are different from conventional explosions. A normal explosive substance uses an external detonating trigger, and smaller quantities of explosive cause smaller explosions (from bombs akin to those used in the second world war, which destroyed buildings, to the cap in a toy pistol). A nuclear bomb doesn’t work like that – at least, not a fission bomb such as the ones set off in Hiroshima and Nagasaki.

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The 9 most powerful nuclear weapon explosions

They are all more powerful than the bombs used on Hiroshima and Nagasaki at the end of WWII.

Castle Bravo

Castle yankee, castle romeo.

The United States and Russia now have thousands of nuclear weapons each, with China , France, the United Kingdom, India, Pakistan, North Korea and Israel also having nukes. The ongoing Russian invasion of Ukraine has sparked fears that such nuclear weapons could end up being used. 

Here, Live Science takes a look at the most powerful nuclear weapons ever detonated — specifically explosions that exceeded 10 megatons. In comparison, estimates for the Hiroshima bomb are around 15 kilotons. Documents from the U.S. Department of Energy and the Russian Federation's Ministry of Defense revealed plenty of high-energy blasts. Even so, there are a number of nuclear weapon detonations whose yields are uncertain, so only those detonations whose yields are known with confidence are included here. All of these behemoth blasts are many times more powerful than those that were used on Hiroshima and Nagasaki at the end of World War II . 

On Oct. 30, 1961, the Soviet Union dropped the most powerful nuclear weapon ever exploded on the archipelago of Novaya Zemlya, north of the arctic circle. Yielding an explosion of 50 megatons the "Tsar Bomba," as it is sometimes called, was about 3,300 times more powerful than the 15 kilotons nuclear weapon dropped on Hiroshima. The hydrogen bomb, designated as the Soviet RDS-220, was also dubbed "Big Ivan" and "Vanya," though "Tsar Bomba" (translated to King of Bombs) is its most popular moniker.

Ironically, the bomb could have been much more powerful. It was designed to have an explosive yield of up to 100 megatons, but it was detonated at 50 megatons, wrote Alex Wellerstein, director of the Science and Technology Studies program at the Stevens Institute of Technology, in an article published in 2021 on the Bulletin of the Atomic Scientists website. The fireball from the explosion was nearly 6 miles (9.7 km) in diameter, which is "large enough to include the entire urban core of Washington or San Francisco, or all of midtown and downtown Manhattan," wrote Wellerstein. 

On Dec. 24, 1962, the Soviet Union dropped a rather unpleasant Christmas present over the test site on the Novaya Zemlya archipelago — which holds the second largest glacier complex in the Arctic, according to a paper published in 2021 in the journal Nature . At 24.2 megatons, this nuclear bomb was less than half as powerful as the "Tsar Bomba" bomb but was still the second most powerful nuclear weapon ever detonated. It also about 1,600 times stronger than the bomb dropped on Hiroshima. 

Because it was the second most powerful nuclear weapon, it didn't get a catchy nickname like the "Tsar Bomba" did; it is simply referred to as "test 219." Test 219 would be one of the last nuclear bombs dropped from the air by the Soviet Union, as a test ban treaty in 1963 banned aboveground testing and future tests were conducted underground. 

On Aug. 5, 1962, the Soviet Union dropped a 21.1 megaton over the Novaya Zemlya archipelago (which is part of the Russian Arctic). The third most powerful nuclear detonation in history, it is simply known as "test 147," again not acquiring a nickname like the "Tsar Bomba" did.

This bomb clocks in as being about 1,400 times as powerful as the one dropped on Hiroshima. Despite its immense power this nuclear detonation is not as well known as others on this list. 

According to the site Nukemap , a nuclear weapon like this that was airburst over Central Park, in New York City, would produce a fireball that would cover all of the park and produce an intense wave of thermal radiation that would cover all of the city and reach as far away as Stamford, New York. Nukemap was created by Alex Wellerstein.  

On Sept. 25, 1962, the Soviet Union dropped a 19.1 megaton nuke over the Novaya Zemlya archipelago. The fourth most powerful nuclear weapon ever detonated it is about 1,270 times more powerful than the Hiroshima bomb. Known simply as "test 173" this bomb never got a nickname. 

An interesting note — a few weeks after this bomb was dropped the Cuban Missile Crisis began — a crisis that brought the Soviet Union and United States to the brink of nuclear war. During the crisis the Soviet Union deployed nuclear missiles to Cuba. President Kennedy considered attacking the sites and ultimately ordered a naval blockade to prevent more nuclear weapons from reaching Cuba. The Soviet Union eventually agreed to take down the missiles in exchange for the United States removing their nuclear missiles from Turkey. 

On March 1, 1954 the United States detonated a 15 megaton nuclear weapon on the Bikini Atoll, in the Marshall Islands , in a test codenamed "Castle Bravo." It was detonated on the surface rather than being dropped by air and is the fifth most powerful nuclear weapon detonation in history. 

The yield was about two and half times greater than expected and resulted in nuclear fallout spreading for about 7,000 square miles (18,130 square kilometers) across the Pacific, leaving residents of the Marshall Islands, U.S. military personnel and the crew of a Japanese fishing trawler exposed to a high level of radiation, according to an article published in 2017 by the Atomic Heritage Foundation. Some residents had to be evacuated, and the people of the Marshall Islands suffered an elevated rate of cancer. 

The Castle Bravo test, and the harm done to the residents, triggered global protests against the testing of nuclear bombs. In future decades, the U.S. government paid compensation to island residents; retired U.S. military personnel launched a case against the government in 1984, alleging that the American government had downplayed the radiation danger. 

On May 5, 1954, another nuclear weapon was detonated on a barge beside the Bikini Atoll. The "Castle Yankee" test resulted in a yield of 13.5 megatons. It is the sixth most powerful nuclear weapon ever detonated in history, being about 900 times more powerful than the one dropped on Hiroshima. In the years that followed, global pressure would mount for a ban on nuclear tests to come into place. 

The Bikini Atoll is a coral reef that surrounds a lagoon. Prior to nuclear testing, people lived on the atoll. The population was removed before the tests and has never been able to return because the atoll is still contaminated with remains from the radioactive fallout. 

On Oct. 23, 1961, the Soviet Union dropped a 12.5 megaton bomb on the Novaya Zemlya archipelago, about 830 times as powerful as the Hiroshima bomb. It is the seventh most powerful nuclear weapon detonated in history. Known as "test 123," it was a prelude to the "Tsar Bomba," which would be dropped in the same area just a week later. 

According to an article published in 1996 in the journal Polar Geography, this archipelago had small populations of people living there prior to nuclear testing. These people engaged in hunting and trapping. 

On March 26, 1954, a nuclear weapon was detonated on a barge off the Bikini Atoll. It yielded an 11 megaton nuclear explosion that was about 730 times as powerful as the Hiroshima bomb. Codenamed "Castle Romeo," the test was carried out just a few weeks after the Castle Bravo test that had spread radioactive fallout across the Marshall Islands. 

According to Nukemap, a nuclear weapon of this intensity airburst over New York City's Central Park would produce a fireball that would cover the park and a wave of intense thermal radiation that would extend as far as Port Chester. 

On Nov. 1, 1952, "Ivy Mike" or "Mike," would become the first thermonuclear weapon (hydrogen bomb) to be fully detonated — yielding a 10.4 megaton explosion, about 690 times the size of the Hiroshima bomb. It was detonated on the surface of the Enewetak atoll on the Marshall Islands. At the time it was detonated, the Korean War was raging and a nuclear arms race had developed between the United States and Soviet Union. 

Whether to develop the hydrogen bomb was a subject of debate within the Truman administration, with some officials pushing against it and others pushing for it, an article on the Atomic Heritage Foundation website noted , with president Truman ultimately deciding to build it. 

Originally published on Live Science .

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Owen Jarus is a regular contributor to Live Science who writes about archaeology and humans' past. He has also written for The Independent (UK), The Canadian Press (CP) and The Associated Press (AP), among others. Owen has a bachelor of arts degree from the University of Toronto and a journalism degree from Ryerson University. 

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Centrus Energy expects to deliver 900 kilograms of high-assay, low-enriched uranium fuel annually from centrifuges at its Piketon, Ohio plant.

Various scenarios to getting to net zero carbon emissions from power generation by 2050 hinge on the success of some hugely ambitious initiatives in renewable energy, grid enhancements, and other areas. Perhaps none of these are more audacious than an envisioned renaissance of nuclear power , driven by advanced-technology reactors that are smaller than traditional nuclear power reactors.

What many of these reactors have in common is that they would use a kind of fuel called high-assay low-enriched uranium (HALEU). Its composition varies, but for power generation, a typical mix contains slightly less than 20 percent by mass of the highly fissionable isotope uranium-235 (U-235). That’s in contrast to traditional reactor fuels, which range from 3 percent to 5 percent U-235 by mass, and natural uranium, which is just 0.7 percent U-235.

Now, though, a paper in Science magazine has identified a significant wrinkle in this nuclear option: HALEU fuel can theoretically be used to make a fission bomb—a fact that the paper’s authors use to argue for the tightening of regulations governing access to, and transportation of, the material. Among the five authors of the paper, which is titled “The Weapons Potential of High-Assay Low-Enriched Uranium,” is IEEE Life Fellow Richard L. Garwin . Garwin was the key figure behind the design of the thermonuclear bomb, which was tested in 1952.

The Science paper is not the first to argue for a reevaluation of the nuclear proliferation risks of HALEU fuel. A report published last year by the National Academies, “Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and the Waste Aspects of Advanced Nuclear Reactors,” devoted most of a chapter to the risks of HALEU fuel. It reached similar technical conclusions to those of the Science article, but did not go as far in its recommendations regarding the need to tighten regulations.

Why is HALEU fuel concerning?

Conventional wisdom had it that U-235 concentrations below 20 percent were not usable for a bomb. But “we found this testimony in 1984 from the chief of the theoretical division of Los Alamos, who basically confirmed that, yes, indeed, it is usable down to 10 percent,” says R. Scott Kemp of MIT, another of the paper’s authors. “So you don’t even need centrifuges, and that’s what really is important here.”

Centrifuges arranged very painstakingly into cascades are the standard means of enriching uranium to bomb-grade material, and they require scarce and costly resources, expertise, and materials to operate. In fact, the difficulty of building and operating such cascades on an industrial scale has for decades served as an effective barrier to would-be builders of nuclear weapons. So any route to a nuclear weapon that bypassed enrichment would offer an undoubtedly easier alternative. The question now is, how much easier?

“It’s not a very good bomb, but it could explode and wreak all kinds of havoc.”

Adding urgency to that question is an anticipated gold rush in HALEU, after years of quiet U.S. government support. The U.S. Department of Energy is spending billions to expand production of the fuel, including US $150 million awarded in 2022 to a subsidiary of Centrus Energy Corp. , the only private company in the United States enriching uranium to HALEU concentrations . (Outside of the United States, only Russia and China are producing HALEU in substantial quantities.) Government support also extends to the companies building the reactors that will use HALEU. Two of the largest reactor startups, Terrapower ( backed in part by Bill Gates ) and X-Energy , have designed reactors that run on forms of HALEU fuel, and have received billions in funding under a DOE program called Advanced Reactor Demonstration Projects .

The difficulty of building a bomb based on HALEU is a murky subject, because many of the specific techniques and practices of nuclear weapons design are classified. But basic information about the standard type of fission weapon, known as an implosion device, has long been known publicly. (The first two implosion devices were detonated in 1945, one in the Trinity test and the other over Nagasaki, Japan.) An implosion device is based on a hollow sphere of nuclear material. In a modern weapon this material is typically plutonium-239 , but it can also be a mixture of uranium isotopes that includes a percentage of U-235 ranging from 100 percent all the way down to, apparently, around 10 percent. The sphere is surrounded by shaped chemical explosives that are exploded simultaneously, creating a shockwave that physically compresses the sphere, reducing the distance between its atoms and increasing the likelihood that neutrons emitted from their nuclei will encounter other nuclei and split them, releasing more neutrons. As the sphere shrinks it goes from a subcritical state, in which that chain reaction of neutrons splitting nuclei and creating other neutrons cannot sustain itself, to a critical state, in which it can. As the sphere continues to compress it achieves supercriticality , after which an injected flood of neutrons triggers the superfast, runaway chain reaction that is a fission explosion. All this happens in less than a millisecond.

The authors of the Science paper had to walk a fine line between not revealing too many details about weapons design while still clearly indicating the scope of the challenge of building a bomb based on HALEU. They acknowledge that the amount of HALEU material needed for a 15-kiloton bomb—roughly as powerful as the one that destroyed Hiroshima during the second World War—would be relatively large: in the hundreds of kilograms, but not more than 1,000 kg. For comparison, about 8 kg of Pu-239 is sufficient to build a fission bomb of modest sophistication. Any HALEU bomb would be commensurately larger, but still small enough to be deliverable “using an airplane, a delivery van, or a boat sailed into a city harbor,” the authors wrote.

They also acknowledged a key technical challenge for any would-be weapons makers seeking to use HALEU to make a bomb: preinitiation. The large amount of U-238 in the material would produce many neutrons, which would likely result in a nuclear chain reaction occurring too soon. That would sap energy from the subsequent triggered runaway chain reaction, limiting the explosive yield and producing what’s known in the nuclear bomb business as a “ fizzle .“ However, “although preinitiation may have a bigger impact on some designs than others, even those that are sensitive to it could still produce devastating explosive power,” the authors conclude.

In other words, “it’s not a very good bomb, but it could explode and wreak all kinds of havoc,” says John Lee , professor emeritus of nuclear engineering at the University of Michigan. Lee was a contributor to the 2023 National Academies report that also considered risks of HALEU fuel and made policy recommendations similar to those of the Science paper.

Critics of that paper argue that the challenges of building a HALEU bomb, while not insurmountable, would stymie a nonstate group. And a national weapons program, which would likely have the resources to surmount them, would not be interested in such a bomb, because of its limitations and relative unreliability.

“That’s why the IAEA [International Atomic Energy Agency], in their wisdom, said, ‘This is not a direct-use material,’” says Steven Nesbit , a nuclear-engineering consultant and past president of the American Nuclear Society , a professional organization. “It’s just not a realistic pathway to a nuclear weapon.”

The Science authors conclude their paper by recommending that the U.S. Congress direct the DOE’s National Nuclear Security Administration ( NNSA ) to conduct a “fresh review” of the risks posed by HALEU fuel. In response to an email inquiry from IEEE Spectrum , an NNSA spokesman, Craig Branson, replied: “To meet net-zero emissions goals, the United States has prioritized the design, development, and deployment of advanced nuclear technologies, including advanced and small modular reactors. Many will rely on HALEU to achieve smaller designs, longer operating cycles, and increased efficiencies over current technologies. They will be essential to our efforts to decarbonize while meeting growing energy demand. As these technologies move forward, the Department of Energy and NNSA have programs to work with willing industrial partners to assess the risk and enhance the safety, security, and safeguards of their designs.”

The Science authors also called on the U.S. Nuclear Regulatory Commission (NRC) and the IAEA to change the way they categorize HALEU fuel. Under the NRC’s current categorization, even large quantities of HALEU are now considered category II , which means that security measures focus on the early detection of theft. The authors want weapons-relevant quantities of HALEU reclassified as category I , the same as for quantities of weapons-grade plutonium or highly enriched uranium sufficient to make a bomb. Category I would require much tighter security, focusing on the prevention of theft.

Nesbit scoffs at the proposal, citing the difficulties of heisting perhaps a metric tonne of nuclear material. “Blindly applying all of the baggage that goes with protecting nuclear weapons to something like this is just way overboard,” he says.

But Lee, who performed experiments with HALEU fuel in the 1980s, agrees with his colleagues. “Dick Garwin and Frank von Hipple [and the other authors of the Science paper] have raised some proper questions,” he declares. “They’re saying the NRC should take more precautions. I’m all for that.”

• The Future of Fission Reactors May Be Small ›
• U.S. Reenters the Nuclear Fuel Game ›
• Uranium fuel planned for high-tech US reactors a weapons risk ... ›
• What is High-Assay Low-Enriched Uranium (HALEU)? | Department ... ›

Glenn Zorpette is editorial director for content development at IEEE Spectrum . A Fellow of the IEEE, he holds a bachelor's degree in electrical engineering from Brown University.

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