A nuclear weapon of the "Little Boy" type, the uranium gun-type detonated over Hiroshima. It is 28 inches in diameter and 120 inches long. "Little Boy" weighed about 9,000 pounds and had a yield approximating 15,000 tons of high explosives. (Copy from U.S. National Archives, RG 77-AEC)

Washington, D.C., August 5, 2005 - Sixty 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]

A nuclear weapon of the "Fat Man" type, the plutonium implosion type detonated over Nagasaki. 60 inches in diameter and 128 inches long, the weapon weighed about 10,000 pounds and had a yield approximating 21,000 tons of high explosives (Copy from U.S. National Archives, RG 77-AEC)

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 made some unsettled readers question the bombings while church groups and a few 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 about 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 journalists continued to engage in the debate. Alperovitz, Bernstein, and Sherwin made new contributions to the debate as did historians, social scientists, and journalists such as Richard B. Frank, Herbert Bix, Sadao Asada, Kai Bird, Robert James Maddox, Robert P. Newman, Robert S. Norris, Tsuyoshi Hagesawa, and J. Samuel Walker.[4] The controversy has revolved around the following, among other, questions:

Taken at Tinian Island on the afternoon of August 5, 1945, this shows the tail of the Enola Gay being edged over the pit and into position to load "Little Boy" into the bomb bay. The weapon is in the pit covered with canvas. Various personnel and guards are standing around the loading area. (Photo from U.S. National Archives, RG 77-BT)

• Were 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 to choose major cities as targets?
• 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 guaranteeing a constitutional monarchy would Japan have surrendered earlier than it did?
• How greatly did the atomic bombings affect 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 shows the "Little Boy" weapon in the pit ready for loading into the bomb bay of Enola Gay. (Photo from U.S. National Archives, RG 77-BT)

This briefing book will not attempt to answer these questions or use primary sources to stake out positions on any of them. Nor will it attempt to substitute for the extraordinarily rich literature on the atomic bombs and the end of World War II. This collection does not attempt to document the origins and development of the Manhattan Project. Nor does it include any of the miscellaneous sources (interviews, documents prepared after the events, post-World War II correspondence, etc.) that participants in the debate have brought to bear in framing their arguments. Instead, by gaining access to a broad range of U.S. and Japanese documents 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 be able to develop their own answers to the questions raised above. The documents may even provoke new questions.

This shows "Little Boy" being raised for loading into the Enola Gay's bomb bay. (Photo from U.S. National Archives, RG 77-BT)

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 not to 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 took the editor to 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 files of the National Security Agency. Private collections were also important such as the Stimson Diary at Yale University (although available on microfilm elsewhere) 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 mushroom cloud billowing up 20,000 feet over Hiroshima on the morning of August 6, 1945 (Photo from U.S. National Archives, RG 77-AEC)

The U.S. documents cited here will be familiar to many expert readers on the Hiroshima-Nagasaki controversy. 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; the documents enable interested readers to form their own judgments about the direction of Japanese diplomacy in the weeks before the atomic bombings. Moreover, 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. This material sheds light on the considerations that induced Japan ’s surrender.

I. Background on the Atomic Project

Document 1: Memorandum from Vannevar Bush and James B. Conant, Office of Scientific Research and Development, to Secretary of War, September 30, 1944, Top Secret
Source: Record Group 77, Records of the Army Corps of Engineers (hereinafter RG 77), Manhattan Engineering District (MED), Harrison-Bundy Files (H-B Files), folder 69

Months before the bomb would be available, key War Department advisers, among others, worried about the political and military problems and possibilities raised by the project—the possibility of enormously powerful hydrogen bombs, enormous military potential, the limits of secrecy, the danger of a global arms race, and the need for international exchange of information and international inspection to stem dangerous nuclear competition. Martin Sherwin and James Hershberg see this memorandum flowing from Bush and Conant’s concern about President Roosevelt's "cavalier" belief that it would be possible to maintain an Anglo-American atomic monopoly after World War II. To disabuse senior officials that such a monopoly was possible, they drafted this memorandum.[6]

The Enola Gay returns to Tinian Island after the strike on Hiroshima. (Photo from U.S. National Archives, RG 77-BT)

Document 2: 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.

Documents 3a-c: President Truman Learns the Secret:

a. Memorandum for the Secretary of War from General L. R. Groves, "Atomic Fission Bombs," April 23, 1945
Source: RG 77, Commanding General’s file no. 24, tab D

b. Memorandum discussed with the President, April 25, 1945
Source: Henry Stimson Diary, Manuscripts and Archives, Yale University Library, Henry Lewis Stimson Papers (microfilm at Library of Congress)

c. Untitled memorandum by General L.R. Groves, April 25, 1945
Source: Record Group 200, Papers of General Leslie R. Groves, Correspondence 1941-1970, box 3, "F"

d. Diary Entry, April 25, 1945
Source: Henry Stimson Diary, Sterling Library, Yale University (microfilm at Library of Congress)

A "Fat Man" test unit being raised from the pit into the bomb bay of a B-29 for bombing practice during the weeks before the attack on Nagasaki. (Photo from U.S. National Archives, RG 77-BT)

Soon after he was sworn in as president, after President Roosevelt's death, Harry Truman learned about the top secret Manhattan Project.  It was not until he received a briefing from Secretary of War Stimson and Manhattan Project chief General Groves, who went through the "back door" to escape the watchful press, that Truman understood the full scope of the enterprise.  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 atomic bomb project from the raw materials to processing nuclear fuel to assembling the weapons to plans for using them, which had already crystallized.   With respect to the last point, the first gun-type weapon "should be ready about 1 August 1945" while an implosion weapon would 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 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, Barton Bernstein finds that Truman "never questioned [the] assumption" that the bomb would and should be used.  Robert S. Norris has also noted that "Truman’s 'decision' was a decision not to override previous plans to use the bomb."[7]

II. Defining Targets

Document 4: 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)

A photo prepared by U.S. Air Intelligence for analytical work on destructiveness of atomic weapons. The total area devastated by the atomic strike on Hiroshima is shown in the darkened area (within the circle) of the photo. The numbered items are military and industrial installations with the percentages of total destruction. (Photo from U.S. National Archives, RG 77-AEC)

In late April, military officers and nuclear scientists met to discuss bombing techniques, target selection, and overall mission requirements.  The discussion of "available targets" included Hiroshima, the "largest untouched targets not on the 21^st Bomber Command priority list."

Document 5: 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)

Discussing the radiological dangers of a nuclear detonation, Oppenheimer explained to General Farrell, Groves's deputy, the need for precautions.

Document 6: 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
Source: RG 77, MED Records, Top Secret Documents, File no. 5d (copy from microfilm)

Scientists and officers held further discussion of bombing mission requirements, including height of detonation, weather, 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.

Document 7: Diary Entries, May 14 and 15, 1945
Source: Henry Stimson Diary, Manuscripts and Archives, Yale University Library, Henry Lewis Stimson Papers (microfilm at Library of Congress)

The polar cap of the "Fat Man" weapon being sprayed with plastic spray paint in front of Assembly Building Number 2. (Photo from U.S. National Archives, RG 77-BT)

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.[8]

Document 8: 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 would have been tested. Alperovitz treats this entry as evidence in support of the atomic diplomacy argument, but other historians, ranging from Robert Maddox to Gabriel Kolko, deny that the timing of the Potsdam conference had anything to do with the goal of using the bomb to intimidate the Soviets.[9]

Document 9: Minutes of Third Target Committee Meeting – Washington, May 28, 1945, Top Secret
Source: RG 77, MED Records, Top Secret Documents, File no. 5d (copy from microfilm)

More updates on training missions, target selection, and conditions required for successful detonation over the target. “Pumpkins” referred to bright orange, pumpkin-shaped high explosive bombs—shaped like the “Fat Man” implosion weapon--used for bombing run test missions.  

Document 10: General Lauris Norstad to Commanding General, XXI Bomber Command, "509^th Composite Group; Special Functions,"May 29, 1945, Top Secret
Source: RG 77, MED Records, Top Secret Documents, File no. 5g (copy from microfilm)

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 crews for successful nuclear strikes.

Document 11: Assistant Secretary of War John J. McCloy, "Memorandum of Conversation with General Marshall 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

Apparently dissenting from the Targeting Committee’s recommendations, Army Chief of Staff George 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 a few figures such as Marshall and Stimson were “caught between an older morality that opposed the intentional killing of noncombatants and a newer one that stressed virtually total war.”[10]

Document 12: "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.”  Bernstein argues that this target choice represented an uneasy endorsement of “terror bombing”--the target was not exclusively military or civilian; nevertheless, workers' housing would include noncombatant men, women, and children.[11]

Document 13:  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 the 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 about “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.”[12]

Document 14: Memorandum from R. Gordon Arneson, Interim Committee Secretary, to Mr. Harrison, June 6, 1945, Top Secret
Source: RG 77, MED Records, H-B files, folder no. 100 (copy from microfilm)

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 criteria and an attack “without prior warning.”

Document 15:  Memorandum of Conference with the President, June 6, 1945, Top Secret
Source: Manuscripts and Archives, Yale University Library, Henry Lewis Stimson Papers (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).[13] 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 older morality.”

III. Debates on Alternatives to First Use and Unconditional Surrender

Document 16: 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 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.  Arthur Compton, the “Met Lab’s” director, 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.[14]

Document 17: 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, Grew’s knowledge of Japanese politics and culture informed his critical 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 argued that the Japanese leadership would “probably not” have “surrendered if the Truman administration had clarified the status of the emperor” when it demanded unconditional surrender.[15]

Document 18: Memorandum from Chief of Staff Marshall to the Secretary of War, 15 June 1945, enclosing "Memorandum of Comments on 'Ending the Japanese War,'" June 14, 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)

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.[16]

Document 19: Memorandum by J. R. Oppenheimer, "Recommendations on the Immediate Use of Nuclear Weapons," June 16, 1945, Top Secret
Source: RG 77, MED Records, H-B files, folder no. 76 (copy from microfilm)

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 20: "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 his military advisers stepped back and considered the implications and requirements of the invasion of Japan. In this meeting with the Joint Chiefs of Staff Truman reviewed plans to land troops on Kyushu on 1 November, heard a range of casualty estimates, and contemplated the possible impact of eventual Soviet entry into the war with Japan. This account hints at discussion of the atomic bomb (“certain other matters”) but no documents disclose that part of the meeting.  This document has figured in the highly 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 post-war estimates were inflated.[17]

This meeting has also played a role in the historical discussions of the alternatives to nuclear weapons use in the summer of 1945.   According to accounts based on post-war recollections and interviews, 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 quashed 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?”[18]

Document 21: Memorandum from R. Gordon Arneson, Interim Committee Secretary, to Mr. Harrison, June 25, 1945, Top Secret
Source: RG 77, MED Records, H-B files, folder no. 100 (copy from microfilm)

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” and urban-industrial targets.  In addition, it recommended revocation of part two of the 1944 Quebec agreement which stipulated that 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.[19]

Document 22: 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 Franck report or not, was that the United States should inform Stalin about 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 23: Memorandum from George L. Harrison to Secretary of War, June 28, 1945, Top Secret, enclosing Ralph Bard "Memorandum on the Use of S-1 Bomb," June 27, 1945
Source: RG 77, MED, H-B files, folder no. 77 (copy from microfilm)

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.  Berstein, however, notes that Bard later denied that he had a meeting with Truman and that White House appointment logs support that claim.[20]

Document 24: 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 staffers, Colonel Fahey, argued against modification of unconditional surrender (see “Appendix ‘C`”). 

Document 25: Assistant Secretary of War John J. McCloy to Colonel Stimson, June 29, 1945, 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 8, Japan (After December 7/41)

McCloy was part of a drafting committee that was working on the text of a proclamation to Japan which would 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 26: Memorandum, "Timing of Proposed Demand for Japanese Surrender," June 29, 1945, 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 8, Japan (After December 7/41)

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 27: 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, engage in hot debate.  

Document 28: 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”.[21]

IV. The Japanese Search for Soviet Mediation

Document 29: "Magic" – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1204 – July 12, 1945, Top Secret Ultra
Source: Record Group 457, Records of the National Security Agency/Central Security Service, "Magic" Diplomatic Summaries 1942-1945, box 18

Since September 1940, under the covername "Magic," U.S. military intelligence had been routinely decrypting the intercepted cable traffic of the Japanese Foreign Ministry. The National Security Agency kept the 'Magic" diplomatic and military summaries classified for many years and did not release the series for 1942 through August 1945 in its entirety until the early 1990s. This 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 its 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" that moderating unconditional surrender and a Soviet declaration of war would have been enough to induce Japan's surrender without the use of the bomb.[22]

Document 30: 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.”  Having analyzed the document closely, Tsuyoshi Hasegawa 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.[23]

Document 31: "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 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 32: 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

The draft of the proclamation to Japan that reached Truman contained language that modified unconditional surrender by promising to retain the emperor.  When former Secretary of State Cordell Hull learned about that development he outlined his objections to Secretary of State Byrnes. The latter was already inclined to reject that part of the draft but Hull’s arguments may have reinforced his decision.

Document 33: "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). [Page 14 missing from original]

Document 34: R. E. Lapp, Leo Szilard et al., "A Petition to the President of the United States," July 17, 1945
Source: RG 77, MED Records, H-B files, folder no. 76 (copy from microfilm)

In a final effort to discourage military use of the bomb, Szilard circulated a petition, which he hoped would reach President Truman, and which was signed by about 68 Manhattan Project scientists, mainly physicists and biologists (copies with the remaining signatures are in the archival file).  Not explicitly rejecting military use, the petition raised questions about an arms race that military use could inspire and called Truman to publicize detailed terms for Japanese surrender.  Truman, already on his way to Europe, never saw the petition.[24]

V. The Trinity Test, the Potsdam Conference, and the Execution Order

Document 35: Cable War 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 on 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][25]

Document 36: 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)

 The first atomic test took place in the New Mexico desert on 16 August.  General Groves prepared for Stimson, then at Potsdam, a detailed account of the “Trinity” test.[26]

Document 37: 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 put rear admiral Sokichi Takagi on sick leave so that he could undertake a secret mission to find a way to end the war. Takaki 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 that follows gives a sense of the state of play for Foreign Minister Togo’s attempt to secure Soviet mediation.  Hasegawa cites 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.[27]  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 contact 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.[28]

Document 38: Truman's Potsdam Diary
Barton J. Bernstein, "Truman At Potsdam: His Secret Diary," Foreign Service Journal, July/August 1980, excerpts, used with author’s permission[29]

Some years after Truman died 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 Truman Library’s web site (for 16 July and 17-30 July respectively).

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 Secretary of War 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.[30]

Document 39: Diary entries for July 16 through 25, 1945
Source: Henry Stimson Diary, Manuscripts and Archives, Yale University Library, Henry Lewis Stimson Papers (microfilm at Library of Congress)

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 17) and the ongoing nuclear deployments for 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 suffice 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.[31]   During a meeting on August 24, Truman agreed with Stimson that Kyoto, Japan’s cultural capital, would not be one of the nuclear targets.  For Stimson destroying that city could have caused such “bitterness” that it might 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.”[32]

Document 40: "Magic" – Diplomatic Summary, War Department, Office of Assistant Chief of Staff, G-2, No. 1214 – July 22, 1945, Top Secret Ultra
Source: Record Group 457, Records of the National Security Agency/Central Security Service, "Magic" Diplomatic Summaries 1942-1945, box 18.

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 accept unconditional surrender except for one provision: the “preservation of the Imperial House.”   Probably