In July 1945, 70 Manhattan Project scientists signed a petition begging President Harry Truman not to use the atomic bomb on Japan without first giving the Japanese a chance to surrender. The petition was passed up the chain of command, deliberately delayed by General Leslie Groves, classified as “Secret” by a War Department assistant, and filed away. It never reached Truman. It was not declassified until September 1958.[s] The men who built the most destructive weapon in history tried to stop its use, and no one in power heard them.
Why Manhattan Project Scientists Built It
Most Manhattan Project scientists were driven by a single fear: that Nazi Germany would build the bomb first. Many were European refugees who had fled fascism. Leo Szilard, a Hungarian physicist who had conceived the nuclear chain reaction in 1933, drafted the famous 1939 letter for Albert Einstein’s signature urging President Roosevelt to begin an atomic weapons program.[s] Joseph Rotblat, a Polish physicist, joined the British Mission to Los Alamos in 1944 specifically because he believed Britain needed a deterrent against a potential German bomb.[s]
The moral calculus was straightforward: build the weapon before Hitler does, or risk civilization. But by late 1944, that calculus collapsed. Allied intelligence indicated that Germany was not close to producing an atomic bomb, and that its serious bomb effort had stalled, though nuclear research continued on a modest scale. The war in Europe was ending. And the bomb was still being built.
The Man Who Walked Away
In March 1944, Rotblat had dinner with General Groves, who remarked that the project’s real objective was to subdue the Soviet Union.[s] Disgusted, Rotblat left the Manhattan Project in December 1944, the only scientist to depart on grounds of conscience.[s] The United States retaliated with a fabricated dossier accusing him of spying for the Soviets, and he was barred from reentering the country until 1964.[s]
Rotblat went on to co-found the Pugwash Conferences on Science and World Affairs in 1957 alongside Bertrand Russell. For decades of work toward nuclear disarmament, he shared the 1995 Nobel Peace Prize.[s] “Science became identified with death and destruction,” he said in his Nobel lecture. Few Americans have heard his name.
Manhattan Project Scientists Sound the Alarm
While Rotblat left, others tried to change the outcome from the inside. In June 1945, a committee led by physicist James Franck produced what became known as the Franck Report, largely written by Eugene Rabinowitch. The report predicted, with remarkable accuracy, a nuclear arms race. It warned that “within ten years, other countries may have nuclear bombs” and urged a demonstration of the weapon over an uninhabited area rather than military use against Japan.[s]
The full text of the Franck Report laid bare the scientists’ reasoning: “We feel compelled to take a more active stand now because the success which we have achieved in the development of nuclear power is fraught with infinitely greater dangers than were all the inventions of the past.”[s] Franck traveled to Washington to deliver the report personally to Secretary of War Stimson. An aide lied and told him Stimson was away from the capital. The report was handed to an assistant instead.[s]
The Petition That Was Buried
When the Franck Report failed, Szilard escalated. On July 17, 1945, he finalized a petition to President Truman signed by 70 Manhattan Project scientists. It argued that atomic attacks on Japan “could not be justified, at least not until the terms which will be imposed after the war on Japan were made public in detail and Japan were given an opportunity to surrender.”[s]
The petition warned that the United States would “bear the responsibility of opening the door to an era of devastation on an unimaginable scale.”[s] Szilard’s original draft had been even stronger, calling for the bomb to be avoided entirely. He moderated the language over several drafts to gain more signatures.[s]
Groves insisted the petition travel through official channels. Szilard passed it to Arthur Compton, who passed it to Kenneth Nichols, who passed it to Groves himself. Groves held it until August. When it finally reached the War Department, Stimson was overseas with Truman at the Potsdam Conference. An assistant stamped it “Secret” and filed it away.[s]
The Decision They Could Not Stop
Meanwhile, the Interim Committee, a civilian advisory body formed in May 1945, had already recommended how the bomb should be used. On June 1, the committee advised that the bomb “should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers’ homes; and that it be used without prior warning.”[s]
The committee’s Scientific Panel, which included Oppenheimer, Fermi, Lawrence, and Arthur Compton, acknowledged that their colleagues’ opinions were “not unanimous” but concluded: “we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.”[s] Edward Teller brought Szilard’s petition to Los Alamos intending to gather signatures, but Oppenheimer talked him out of it, arguing that “scientists have no business to meddle in political pressure of that kind.”[s]
On August 6 and 9, 1945, the United States dropped atomic bombs on Hiroshima and Nagasaki.
After the Flash
Weeks after Hiroshima, Oppenheimer met President Truman in the White House. He told the president: “I feel I have blood on my hands.” Truman was furious. He later told aides: “I don’t want to see that son of a bitch in this office ever again.”[s] Oppenheimer would go on to oppose the hydrogen bomb, only to have his security clearance revoked in a humiliating 1954 hearing.
Other Manhattan Project scientists channeled their guilt into institution-building. On September 26, 1945, a group from the University of Chicago formed the Atomic Scientists of Chicago. By December, they published the first issue of the Bulletin of the Atomic Scientists.[s] In 1947, the Bulletin introduced the Doomsday Clock, set at seven minutes to midnight. As of January 2026, it stands at 85 seconds.
Rabinowitch, who had authored the Franck Report, became the Bulletin‘s editor. He later remembered the summer of 1945 as marked by “the feeling that we were surrounded by a kind of soundproof wall so that you could write to Washington or go to Washington and talk to somebody but you never got any reaction back.”[s]
What They Knew, and When
The Manhattan Project scientists who protested were not naive idealists who woke up too late. They understood the physics of what they were building, predicted the arms race that would follow, and tried to alter the course of events through every channel available to them. Szilard began raising concerns months before Trinity. The Franck Report predicted nuclear proliferation within a decade; the Soviet Union tested its first bomb four years later. The petition’s warning about “an era of devastation on an unimaginable scale” reads today less like rhetoric and more like prophecy.[s]
Their failure was not intellectual but institutional. The military chain of command was designed to move information upward; in this case, it was designed to keep it from arriving. Groves saw dissent as a security risk. Compartmentalization, the same operational principle that kept bomb workers from knowing what they were building, also kept the petition from gaining traction beyond Chicago and Oak Ridge.[s]
The question the Manhattan Project scientists pose to the present is not whether they should have built the bomb. Given what they knew about Germany in 1942, most would build it again. The question is what happens when the reason for building disappears, and the machine keeps running anyway.
On July 17, 1945, Leo Szilard finalized a petition to President Truman signed by 70 Manhattan Project scientists urging restraint in the use of atomic weapons against Japan. The document traveled from Szilard to Arthur Compton to Kenneth Nichols to General Leslie Groves, who held it until August. When it finally reached the War Department, Stimson’s assistant classified it “Secret” and filed it. The petition was not declassified until September 1958.[s] This bureaucratic burial represents one of several documented attempts by Manhattan Project scientists to influence the decision to use atomic weapons, all of which failed to reach the principal decision-makers.
The Shifting Rationale: Manhattan Project Scientists and the German Bomb
The original justification for the Manhattan Project was a German nuclear threat. Leo Szilard had drafted the 1939 Einstein letter to Roosevelt specifically on the premise that Germany might develop fission weapons.[s] By late 1944, the Alsos Mission had confirmed that Germany’s nuclear program was far less advanced than feared. This created a moral crisis for scientists whose participation had been predicated on deterrence.
Joseph Rotblat’s case is instructive. A Polish physicist working with the British Mission at Los Alamos, Rotblat left the project in December 1944 when Germany’s nuclear incapacity became clear.[s] His departure was accelerated by a March 1944 dinner with General Groves, during which Groves stated that the project’s real purpose was to “subdue the Soviets.”[s] Rotblat was the only scientist to leave on grounds of conscience; authorities responded by fabricating espionage allegations that barred him from the United States until 1964. He later co-founded the Pugwash Conferences (1957) and shared the 1995 Nobel Peace Prize.[s]
The Franck Report: Predicting Proliferation
The most substantive policy intervention by Manhattan Project scientists was the Franck Report of June 11, 1945, produced by a committee chaired by James Franck and largely written by Eugene Rabinowitch. The report addressed the Secretary of War directly and made several claims that proved prescient.
First, it predicted nuclear proliferation: “Within ten years, other countries may have nuclear bombs, each of which, weighing less than a ton, could destroy an urban area of more than ten square miles.”[s] The Soviet Union detonated its first device in August 1949, four years later. Second, the report argued that secrecy was futile because “the fundamental facts of nuclear power are a subject of common knowledge” across Allied and Soviet scientific communities.[s] Third, it proposed a demonstration over an uninhabited area as an alternative to military use.
The report’s preamble is notable for its framing of scientific responsibility: “Scientists have often before been accused of providing new weapons for the mutual destruction of nations… We feel compelled to take a more active stand now because the success which we have achieved in the development of nuclear power is fraught with infinitely greater dangers than were all the inventions of the past.”[s]
Franck traveled to Washington to present the report to Secretary Stimson on June 12. A Stimson aide falsely told him the Secretary was out of the capital. Arthur Compton attached a cover note criticizing the committee for “not taking into account the probable net saving of many lives.”[s] It is uncertain whether Stimson ever read the report.
The Szilard Petition: Chain of Command as Silencing Mechanism
The failure of the Franck Report prompted Szilard to pursue a direct appeal. His petition of July 17, 1945, signed by 70 colleagues at the Chicago Met Lab, argued that attacks “could not be justified, at least not until the terms which will be imposed after the war on Japan were made public in detail and Japan were given an opportunity to surrender.”[s]
The petition went through several drafts. Szilard’s original version called for avoiding the bomb entirely; the final version adopted a more moderate position to broaden its signatories.[s] At Oak Ridge, Eugene Wigner circulated the petition and gained additional signatures before military authorities halted distribution, arguing it was a security risk because it implied the existence of a usable weapon.[s]
At Los Alamos, Edward Teller intended to circulate the petition but was dissuaded by Oppenheimer, who argued that “scientists have no business to meddle in political pressure of that kind.” Teller later called this a moment of shame: “I am ashamed to say that he managed to talk me out of the right intention.”[s]
Groves’s insistence on official channels was the decisive factor. The petition moved from Szilard to Compton to Nichols to Groves, who delayed transmission until August. When it reached Stimson’s office, the Secretary was at Potsdam with Truman. It was stamped “Secret” and filed.[s] Groves’s compartmentalization policy, designed to limit knowledge of the bomb’s nature, also limited the pool of potential signatories.
The Interim Committee and the Scientific Panel
The recommendation to use the bomb without warning was made on June 1, 1945 by the Interim Committee, a civilian advisory body chaired by Secretary Stimson. The committee advised Stimson that “the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers’ homes; and that it be used without prior warning.”[s]
The committee’s Scientific Panel (Oppenheimer, Fermi, Lawrence, Arthur Compton) acknowledged internal dissent but concluded: “we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.”[s] Groves later acknowledged that the committee was formed partly “to make certain that the American people as well as the leaders of other nations would realize that the very important decision as to the use of the bomb were not made by the War Department alone.”[s]
Historian Kai Bird and Martin Sherwin documented that Groves privately acknowledged the committee’s function was partly political cover: the perception of civilian deliberation over what was, in practice, a military decision already in motion.[s]
Aftermath: From Guilt to Institutions
After Hiroshima, Oppenheimer told President Truman, “I feel I have blood on my hands.” Truman responded that the blood was on his own hands, and later told aides he never wanted “to see that son of a bitch in this office ever again.”[s] Oppenheimer’s subsequent opposition to the hydrogen bomb led to his security clearance being revoked in 1954.
The institutional legacy of the Manhattan Project scientists’ dissent proved more durable than their wartime protests. On September 26, 1945, Chicago Met Lab veterans formed the Atomic Scientists of Chicago. By December 10, they published the first Bulletin of the Atomic Scientists, with Rabinowitch as editor.[s] In 1947, the Bulletin introduced the Doomsday Clock at seven minutes to midnight. Rotblat and Russell launched the Pugwash Conferences in 1957, creating the first Track 2 diplomacy channels between Soviet and American scientists.[s]
These institutions influenced decades of arms control negotiations, from the Limited Test Ban Treaty (1963) to the Comprehensive Test Ban Treaty (1996). The personal relationships forged at Pugwash between Soviet and American scientists proved, in the Arms Control Association’s assessment, “essential to progress on arms control.”[s]
Historiographic Significance
The moral reckoning of Manhattan Project scientists challenges the popular narrative that atomic weapons were an unquestioned wartime necessity. The documentary record shows sustained, organized dissent that was systematically blocked by military authorities. The Franck Report predicted the central dynamics of the Cold War. The Szilard petition articulated a framework for moral restraint in the use of new weapons. Both documents were suppressed through bureaucratic mechanisms rather than refuted on their merits.
Rabinowitch’s recollection captures the structural problem: “the feeling that we were surrounded by a kind of soundproof wall so that you could write to Washington or go to Washington and talk to somebody but you never got any reaction back.”[s] The Manhattan Project scientists’ experience established a template for the tension between technical expertise and political authority that persists in debates over artificial intelligence, biological weapons, and climate science.
