The S-1 Executive Committee laid the groundwork for the Manhattan Project by initiating and coordinating the early research efforts in the United States, and liaising with the Tube Alloys Project in Britain.
In the wake of the discovery of nuclear fission in December 1938, the possibility that Nazi Germany might develop nuclear weapons prompted Leo Szilard and Eugene Wigner to draft the Einstein–Szilárd letter to the president of the United States, Franklin D. Roosevelt, in August 1939. In response, the Advisory Committee on Uranium was created at the National Bureau of Standards under the chairmanship of Lyman J. Briggs to determine the feasibility of nuclear weapons. In June 1940, the National Defense Research Committee (NDRC) was created to coordinate defense-related research, and the Advisory Committee on Uranium became the Uranium Committee of the NDRC. In June 1941, Roosevelt created the Office of Scientific Research and Development under the leadership of Vannevar Bush (OSRD), at it incorporated the NDRC, now under James B. Conant. The Uranium Committee became the Uranium Section of the OSRD, which was soon renamed the S-1 Section for security reasons. By May 1942, it was felt that the S-1 Section had become too unwieldy, and in June 1942, was replaced by the smaller S-1 Executive Committee.
The feasibility of nuclear weapons was demonstrated by the British MAUD Committee, and its results were shared with the Advisory Committee on Uranium by the Tizard Mission. The S-1 Section coordinated research into nuclear weapons in United States, in cooperation with the British Tube Alloys project. The United States Army created the Manhattan District in June 1942, and took over responsibility for the development of nuclear weapons from the S-1 Executive Committee in September 1942. The OSRD's S-1 research and development contracts were terminated as they lapsed, and production contracts were terminated and transferred to the Army. Although the S-1 Executive Committee remained as an advisory body, it became inactive. The OSRD and NDRC continued to influence the Manhattan Project through the participation of Bush and Conant in the Military Policy Committee that controlled what became the Manhattan Project.
Origins The discovery of nuclear fission in December 1938, reported in the January 6, 1939 issue of Die Naturwissenschaften by Otto Hahn, and Fritz Strassmann, and its correct identification as nuclear fission by Lise Meitner in the February 11, 1939 issue of Nature, generated intense interest among physicists. Even before publication, the news was brought to the United States by Danish physicist Niels Bohr, who opened the fifth Washington Conference on Theoretical Physics with Enrico Fermi on January 26, 1939. The results were quickly corroborated by experimental physicists, most notably Fermi and John R. Dunning at Columbia University.
The possibility that Nazi Germany might develop nuclear weapons was particularly alarming to refugee scientists from Germany and other fascist countries, many of whom had left Europe in the 1930s. Two of them, Leo Szilard and Eugene Wigner drafted the Einstein–Szilárd letter to the President of the United States, Franklin D. Roosevelt. It advised Roosevelt of the existence of the German nuclear weapon project, warned that it was likely the Germans were working on an atomic bomb using uranium, and urged that the United States secure sources of uranium and conduct research into nuclear weapon technology. The letter was signed by Albert Einstein on August 2, 1939, but its delivery was delayed because of the outbreak of World War II in Europe with the German invasion of Poland in September 1939. The letter was eventually hand-delivered to Roosevelt by the economist Alexander Sachs on October 11, 1939. On that date he met with the President, the President's secretary, Brigadier General Edwin "Pa" Watson, and two ordnance experts, Army Lieutenant Colonel Keith F. Adamson and Navy Commander Gilbert C. Hoover. Roosevelt summed up the conversation as: "Alex, what you are after is to see that the Nazis don't blow us up." He told Watson: "This requires action."
Advisory Committee on Uranium As a result of the letter Roosevelt asked scientist Lyman J. Briggs, the director of the National Bureau of Standards, to organize an Advisory Committee on Uranium. Federal advisory committees had been a feature of the federal government since 1794, when George Washington had appointed one to investigate the Whiskey Rebellion. Most are short-lived, terminating after a couple of years, with their membership changing when a new president takes office. The committee consisted of Briggs, Adamson and Hoover. Its first meeting was held on October 21, 1939, at the National Bureau of Standards in Washington, D.C. In addition to the committee members, it was attended by physicists Fred L. Mohler from the National Bureau of Standards and Richard B. Roberts from the Carnegie Institution of Washington, and Szilárd, Wigner and Edward Teller. Einstein was invited but declined to attend. Adamson was skeptical about the prospect of building an atomic bomb, but was willing to authorize $6,000 ( current dollars) for the purchase of uranium and graphite for Szilárd and Fermi's experiments into producing a nuclear chain reaction at Columbia University.
The Advisory Committee on Uranium reported to the President on November 1, 1939. While acknowledging that the science was unproven and that nuclear chain reaction was no more than a theoretical possibility, it foresaw that nuclear energy might be used as propulsion for submarines, and that an atomic bomb "would provide a possible source of bombs with a destructiveness vastly greater than anything now known." The committee recommended that the government purchase of uranium oxide and of graphite for chain reaction experiments. It also recommended that Einstein, Karl Compton, George B. Pegram, and Sachs be added to the committee. When he read the report, Sachs felt that it was too academic and failed to make its points forcefully.
Experiments with the fission of uranium were already proceeding at universities and research institutes in the United States. Alfred Lee Loomis was supporting Ernest Lawrence at the Berkeley Radiation Laboratory. Vannevar Bush was also doing similar research at the Carnegie Institution. At Columbia, while Fermi and Szilard investigated the possibility of creating a nuclear chain reaction, Dunning considered the possibility, advanced by Niels Bohr and John A. Wheeler but discounted by Fermi, that it was the rare uranium-235 isotope of uranium that was primarily responsible for fission. He had Alfred O. C. Nier from the University of Minnesota prepare samples of uranium enriched in uranium-234, uranium-235 and uranium-238 using a mass spectrometer.
These were ready in February 1940, and Dunning, Eugene T. Booth and Aristid von Grosse then carried out a series of experiments. They demonstrated that uranium-235 was indeed primarily responsible for fission with slow neutrons, but were unable to determine precise neutron capture cross sections because their samples were not sufficiently enriched. Pegram forwarded the results to Briggs on March 11, 1940; they were subsequently published to the Physical Reviews March 15 and April 15, 1940 issues. Briggs reported to Watson on April 9 that it was doubtful that a chain reaction could be initiated in uranium without uranium enrichment, and therefore urged that research be undertaken into isotope separation technology. Nier, Booth, Dunning and von Grosse's results were discussed by Jesse Beams, Ross Gunn, Fermi, Nier, Merle Tuve and Harold Urey at the spring meeting of the American Physical Society in Washington, D.C., in the last week of April 1940. The New York Times reported that conferees argued "the probability of some scientist blowing up a sizable portion of the earth with a tiny bit of uranium."
The Advisory Committee on Uranium met again at the National Bureau of Standards on April 27, 1940. This time they were joined by Rear Admiral Harold G. Bowen, Sr., the director of the Naval Research Laboratory (NRL), along with Sachs, Pegram, Fermi, Szilard, and Wigner. Once again, Einstein, although invited, declined to attend. The meeting highlighted differences between the optimistic Szilard and Sachs, and the more cautious Fermi. The committee agreed to proceed with the work at Columbia, which it hoped would demonstrate whether or not a chain reaction was possible. Bowen and Gunn suggested the creation of a scientific subcommittee to advise the Advisory Committee on Uranium. Tuve and Vannevar Bush at the Carnegie Institution, expressed interest in this, and Briggs created it. Chaired by Briggs, its membership consisted of Urey, Pegram, Tuve, Beams, Gunn, and Gregory Breit. The scientific subcommittee met for the first time on June 13, 1940, at the National Bureau of Standards. It reviewed the work thus far and recommended increased support for research into both nuclear chain reactions and isotope separation.
The German invasion of Belgium in May 1940 generated concern over the fate of uranium ore from the Belgian Congo, the world's largest source; the subsequent Battle of France created alarm in the administration over the direction the war was taking. On June 12, 1940, Bush and Harry Hopkins went to the president with a proposal to create a National Defense Research Committee (NDRC) to coordinate defense-related research. The NDRC was formally created on June 27, 1940, with Bush as its chairman. It immediately absorbed the Advisory Committee on Uranium, which was indeed one of its purposes. Bush immediately reorganised the Advisory Committee on Uranium as the NDRC Committee on Uranium, reporting directly to him. Briggs remained chairman, but Hoover and Adamson were dropped from its membership, while Tuve, Pegram, Beams, Gunn, and Urey were added. For security reasons, no foreign-born scientists were appointed to the Uranium Committee. Publication of research into uranium, fission and isotope separation was now banned.
MAUD committee Meanwhile, Otto Frisch and Rudolf Peierls, two researchers at the University of Birmingham in England, who ironically had been assigned to investigate nuclear weapons by Mark Oliphant because, as enemy aliens in Britain, they were ineligible to participate in secret war work, issued the Frisch–Peierls memorandum in March 1940. The memorandum contradicted the common thinking of the time that many tons of uranium would be needed to make a bomb, requiring delivery by ship. The calculation in the memorandum showed that a bomb might be possible using as little as of pure uranium-235, which would be quite practical for aircraft to carry.
Oliphant took the memorandum on to Henry Tizard, and the MAUD Committee was established to investigate further. It concluded that an atomic bomb was not only technically feasible, but could be produced in as little as two years. The Committee unanimously recommended pursuing the development of an atomic bomb as a matter of urgency, although it recognised that the resources required might be beyond those available to Britain. The MAUD Committee completed the MAUD report on July 15, 1941, and disbanded. The report had two parts; the first concluded that a uranium-235 bomb could be feasible in as little as two years using of uranium-235 with a yield equivalent to ; the second concluded that the controlled fission be a source of energy for powering machines and a source of radio-isotopes. As a result of the MAUD Committee report, the British started an atomic bomb program under the codename Tube Alloys.
Further British developments