Experiments with the fission of uranium were already going on at universities and research institutes in the United States. Alfred Lee Loomis was supporting Ernest Lawrence at Berkeley Radiation Laboratory and Enrico Fermi at Columbia. Vannevar Bush was also doing similar research at Washington, D.C.-based Carnegie Institution. After the April 29, 1940 spring meeting of the American Physical Society, 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 idea that a uranium-235 nuclear fission chain reaction could be used to make a bomb was sweeping the nation.
Four aspects of uranium seem to be critical from the start:
Frisch and Peierls's professor, Marcus Oliphant, passed the memorandum on to Henry Tizard, chairman of the Committee on the Scientific Survey of Air Defence who requested the MAUD Committee be established secretly. The first meeting was on April 10, 1940 and the committee consisted of Sir George Paget Thomson as chairman and Marcus Oliphant, Patrick Blackett, James Chadwick, Philip Moon, and John Cockcroft as members. Ralph H. Fowler was also asked to send the progress reports to Lyman Briggs.
On April 14, 1941, Lyman Briggs received a note from Eugene Wigner, stating:
In the meantime, the NDRC under the leadership of Vannevar Bush was also exploring the possibility of using nuclear power for peaceful energy. A favorable report by Arthur Compton and the National Academy of Sciences was issued May 17, 1941, and after consultation with Roosevelt, Bush created the Office of Scientific Research and Development. On July 1, 1941, Bush assumed responsibility for all fission research and the Advisory Committee became the S-1 project of the NDRC. with Lyman Briggs reporting to Bush.
Marcus Oliphant came to the United States from England in August 1941 to find out why Briggs and his committee were apparently ignoring the Maud Report. Oliphant discovered to his dismay that the reports and other documents sent directly to Briggs had not been shared with the Advisory Committee. Oliphant then met with the Uranium Committee and his colleagues Ernest Lawrence, James Conant and Enrico Fermi to explain the urgency. In these meetings Oliphant spoke of a "bomb" with certainty and explained that Britain did not have the resources to undertake the project so it was up to the United States.
The next day, the Japanese Empire's attack on Pearl Harbor led to the United States entry into the war. Four days later, Germany declared war on the United States. On December 18, 1941, a meeting is held where the S-1 project is dedicated to development of a uranium bomb.
As a result of the MAUD Report, the British had started a uranium bomb program referred to by the codename Tube Alloys. Perceived slowness on the part of the United States had become a contentious issue between American and British scientists. Upon entry into the war, the U.S. placed increasing importance on working cooperatively with the British program. Roosevelt wrote a note to Winston Churchill outline increased U.S.-UK cooperation, but was rebuffed by Churchill. Apparently the British felt the U.S. could add little to the effort at that point. This rebuff turned out to be a major blunder as the U.S. effort quickly caught up with the British effort, and the British realised that their pioneering effort would have no value if it were not quickly capitalized. Leadership of the uranium bomb project in the U.S. had eventually switched to U.S. Army General Leslie Groves, who in his own words had never trusted the British (or anyone else).
On June 17, 1942, Roosevelt approved a proposal by Bush to dissolve the original S-1 Section and created the S-1 Executive Committee, chaired by James B. Conant, with the membership of Briggs, Compton, Urey, Lawrence, and Edgar Murphee. The program entered into increased cooperation between the OSRD and the U.S. Army.
On August 13, 1942, the Manhattan Project was created by the U.S. Army Corps of Engineers, and on September 17, 1942, command of the district was given to Groves. The S-1 Executive Committee created two more secret sites: "Site X" in Tennessee (Oak Ridge, Tennessee), where uranium-235 isotope separation was carried out at the Y-12, K-25, and S-50 sites, and "Site Y," a secret laboratory at Los Alamos in northern New Mexico (later Los Alamos National Laboratory), where the bomb design was developed.
As the Army role in the project grew larger, the role of the OSRD became more advisory. Eventually, in May 1943, the Army took full control over the OSRD's research and development contracts, and as such the S-1 Executive Committee became essentially inactive though never formally dissolved. Bush, Conant, and other OSRD insiders continued their influence in the Manhattan Project through their participation in the Military Policy Committee.