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    Manhattan Project: Einstein's Letter, 1939



    Atomic Discoveries Early Government Support Difficult Choices The Uranium Path to the Bomb The Plutonium Path to the Bomb


    Bringing It All Together


    Dawn of the Atomic Era Postscript -- The Nuclear Age


    Events > Early Government Support, 1939-1942

    Einstein's Letter, 1939Early Uranium Research, 1939-1941Piles and Plutonium, 1939-1941Reorganization and Acceleration, 1940-1941The MAUD Report, 1941A Tentative Decision to Build the Bomb, 1941-1942

    On October 11, 1939, Alexander Sachs, Wall Street economist and longtime friend and unofficial advisor to President Franklin Delano Roosevelt, met with the President to discuss a letter written by Albert Einstein the previous August (right).  Einstein had written to inform Roosevelt that recent research on fission chain reactions utilizing uranium made it probable that large amounts of power could be produced by a chain reaction and that, by harnessing this power, the construction of "extremely powerful bombs" was conceivable.  Einstein believed the German government was actively supporting research in this area and urged the United States government to do likewise.  Sachs read from a cover letter he had prepared and briefed Roosevelt on the main points contained in Einstein's letter. Initially the President was noncommittal and expressed concern over locating the necessary funds, but at a second meeting over breakfast the next morning Roosevelt became convinced of the value of exploring atomic energy.

    Einstein drafted his famous letter with the help of the Hungarian émigré physicist Leo Szilard, one of a number of European scientists who had fled to the United States in the 1930s to escape Nazi and Fascist repression.  Szilard was among the most vocal of those advocating a program to develop bombs based on recent findings in nuclear physics and chemistry.  Those like Szilard and fellow Hungarian refugee physicists Edward Teller and Eugene Wigner regarded it as their responsibility to alert Americans to the possibility that German scientists might win the race to build an atomic bomb and to warn that Hitler would be more than willing to resort to such a weapon.  But Roosevelt, preoccupied with events in Europe, took over two months to meet with Sachs after receiving Einstein's letter.  Szilard and his colleagues interpreted Roosevelt's inaction as unwelcome evidence that the President did not take the threat of nuclear warfare seriously.

    Roosevelt (right) wrote Einstein back on October 19, 1939, informing the physicist that he had set up a committee consisting of civilian and military representatives to study uranium.  Events proved that the President was a man of considerable action once he had chosen a direction.  In fact, Roosevelt's approval of uranium research in October 1939, based on his belief that the United States could not take the risk of allowing Hitler to achieve unilateral possession of "extremely powerful bombs," was merely the first decision among many that ultimately led to the establishment of the Manhattan Project.

    Einstein's Letter, 1939Early Uranium Research, 1939-1941Piles and Plutonium, 1939-1941Reorganization and Acceleration, 1940-1941The MAUD Report, 1941A Tentative Decision to Build the Bomb, 1941-1942  NextSources and notes for this page.

    The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources, publication: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), vii.  Click here for more information on the photograph of the letter.  The photograph of Albert Einstein with Leo Szilard is courtesy the Federation of American Scientists.  The portrait of Franklin Roosevelt is courtesy the Center for the Study of Intelligence, Central Intelligence Agency.

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    Source : www.osti.gov

    Einstein and the Manhattan Project

    Einstein expressed regret for urging President Roosevelt to research atomic weapons.

    The Manhattan Project

    Part of the Einstein exhibition.


    In 1938, three chemists working in a laboratory in Berlin made a discovery that would alter the course of history: they split the uranium atom. The energy released when this splitting, or fission, occurs is tremendous--enough to power a bomb. But before such a weapon could be built, numerous technical problems had to be overcome.

    President Franklin Delano Roosevelt

    Photo: FDR Library Archives

    When Einstein learned that the Germans might succeed in solving these problems, he wrote to President Franklin Roosevelt with his concerns. Einstein's 1939 letter helped initiate the U.S. effort to build an atomic bomb, but work proceeded slowly at first. Two other findings in 1940 and 1941 demonstrated conclusively that the bomb was feasible and made building the bomb a top priority for the United States: the determination of the "critical mass" of uranium needed and the confirmation that plutonium could undergo fission and be used in a bomb. In December 1941, the government launched the Manhattan Project, the scientific and military undertaking to develop the bomb.

    A Letter to the President

    In August 1939, Einstein wrote to U.S. President Franklin Roosevelt to warn him that the Nazis were working on a new and powerful weapon: an atomic bomb. Fellow physicist Leo Szilard urged Einstein to send the letter and helped him draft it.

    Einstein: A Security Risk

    In July 1940, the U.S. Army Intelligence office denied Einstein the security clearance needed to work on the Manhattan Project. The hundreds of scientists on the project were forbidden from consulting with Einstein, because the left-leaning political activist was deemed a potential security risk.

    Photo: U.S. National Archives

    August 6, 1945

    First atomic bomb dropped on Hiroshima, Japan

    "Woe is me."—Albert Einstein, upon hearing the news of the Hiroshima bombing

    The Bombing of Japan

    On August 9, 1945, the United States dropped an atomic bomb on the city of Nagasaki, Japan, three days after bombing Hiroshima. By the end of 1945, an estimated 200,000 people had died in the two cities.

    Einstein and the Nuclear Age

    Although he never worked directly on the atomic bomb, Einstein is often incorrectly associated with the advent of nuclear weapons. His famous equation E=mc2 explains the energy released in an atomic bomb but doesn't explain how to build one. He repeatedly reminded people, "I do not consider myself the father of the release of atomic energy. My part in it was quite indirect." Nevertheless, Einstein was frequently asked to explain his role—as he was when a Japanese magazine editor asked him, "Why did you cooperate in the production of atomic bombs, knowing full well their... destructive power?"

    Einstein's answer was always that his only act had been to write to President Roosevelt suggesting that the United States research atomic weapons before the Germans harnessed this deadly technology. He came to regret taking even this step. In an interview with Newsweek magazine, he said that "had I known that the Germans would not succeed in developing an atomic bomb, I would have done nothing."

    More From the Museum

    Library Fun Finds 4.1.22


    Source : www.amnh.org

    The Einstein

    In 1939, Albert Einstein sent FDR a letter urging the US conduct research into an atomic bomb.


    Atomic Heritage Foundation

    In partnership with the National Museum of Nuclear Science & History


    Join Today as an Atomic History Patron Member

    The Einstein-Szilard Letter - 1939

    The Einstein-Szilard Letter - 1939 The Einstein-Szilard Letter - 1939

    History Page Type:

    Manhattan Project History


    Leo SzilardAlbert EinsteinEdward TellerEugene Wigner


    Tuesday, July 18, 2017

    The Einstein-Szilard letter to President Roosevelt changed the course of history by prompting American government involvement in nuclear research. The letter led to the establishment of the Manhattan Project. By the summer of 1945, the United States had built the world’s first atomic bomb.

    Origins of the Letter

    The announcement in early 1939 that German scientists Otto Hahn and Fritz Strassmann had discovered fission prompted fears that Germany might develop an atomic bomb. Among those concerned was physicist Leo Szilard, who soon contacted fellow scientists Edward Teller and Eugene Wigner to plan an appropriate course of action. (The trio, all Hungarian-born, was dubbed the “Hungarian conspiracy” by Merle Tuve.)

    As Szilard remembered, their primary concern was “what would happen if the Germans got hold of large quantities of the uranium which the Belgians were mining in the Congo. So we began to think, through what channels could we approach the Belgian government and warn them against selling any uranium to Germany?” (Rhodes 303).

    Enter Albert Einstein

    The scientists decided that Albert Einstein, who personally knew the Queen of Belgium, would be the ideal person to send warning of the German threat. Szilard and Wigner met Einstein in early July in a cabin in Long Island, NY, where Einstein was on vacation. While Einstein was unwilling to directly contact the queen, he agreed to write a letter to the Ambassador of Belgium, and dictated a first draft to Wigner.

    Soon after, Szilard also spoke with Alexander Sachs, an economist and a close friend of President Franklin Delano Roosevelt. Sachs recommended that they also write to FDR, promising “that if we gave him a statement he would make sure it reached Roosevelt in person” (306).

    Using Einstein’s draft to the Belgian Ambassador, Szilard began crafting a letter to the president. On July 30, he again met with Einstein in his Long Island cabin along with Edward Teller (“I entered history as Szilard’s chauffeur,” quipped Teller). They decided that Sachs could serve as the middleman to deliver the letter to FDR, and sent him a final draft on August 15. As Sachs explained, “I was the right person to make the relevant elaborate scientific material intelligible to Mr. Roosevelt. No scientist could sell it to him” (313). To read the letter, click here.

    Changing History

    Sachs was adamant that he should deliver the letter to President Roosevelt in person and that he should actually read it aloud to him. Sachs noted, “Our social system is such that any public figure [is] punch-drunk with printer’s ink…This was a matter that the Commander in Chief and the head of the Nation must know. I could only do it if I could see him for a long stretch and read the material so itcame in by way of the ear and not as a soft mascara on the eye” (309).

    Nevertheless, the outbreak of World War II made it impossible for Sachs to secure a meeting with the president in August or September. Szilard grew increasingly impatient and even considered finding a different messenger, but on October 11, 1939, Sachs finally met with President Roosevelt to deliver the letter.

    Rather than presenting the letter, Sachs instead put forward his own summary of its conclusions. In an effort to balance what he later called the “two poles of good and evil,” Sachs first explained the peaceful prospects of atomic energy such as nuclear power and medicine before turning his attention to “bombs of hitherto unenvisaged potency of scope” (313). Sachs concluded by noting, “Personally I think there is no doubt that sub-atomic energy is available all around us, and that one day man will release and control its almost infinite power. We cannot prevent him from doing so and can only hope that he will not use it exclusively in blowing up his next door neighbor” (314).

    “Alex,” the president said, “What you are after is to see the Nazis don’t blow us up.”

    “Precisely,” Sachs replied.

    Roosevelt then called in his aide, General Edwin "Pa" Watson: "Pa! This requires action!”


    While other efforts were made to push the U.S. government into atomic research, such as the British MAUD Committee Report, there is no doubt that the Einstein-Szilard letter was vital. President Roosevelt quickly established an advisory Uranium Committee, and the establishment of the S-1 Committee in 1941 marked an official shift from the research to the development phase of the project.

    Although the letter was largely the result of Szilard’s fears of a German atomic bomb, the German nuclear program, which had little governmental support, never came remotely close to developing one. By 1945, Szilard instead feared the use of an American bomb. During the months before the Trinity test in July, Szilard drafted a petition among the Manhattan Project scientists in an attempt to avert wartime use of the bomb against Japan. Nevertheless, it was never seen by President Truman or Secretary of War Henry L. Stimson before the first atomic bomb was dropped on Hiroshima.

    Source : www.atomicheritage.org

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