an atomic bomb could be created from a small amount of fissile uranium-235. Based on the information at hand, they calculated that less than 1 kg would be required. The true figure for the critical mass is about four times as large; but until then it had been assumed that such a bomb would require many tons of uranium, and consequently was impractical to build and use. They went on to estimate the size of the explosion, and its physical, military and political effects. The Frisch–Peierls memorandum was pivotal in igniting the interest of first the British and later the American authorities in atomic weapons. In 1941 its findings made their way to the United States through the report of the MAUD Committee, an important trigger in the establishment of the Manhattan Project and the subsequent development of the atomic bomb. With the Frisch-Peierls memorandum and the MAUD Committee report, the British and American scientists were able to begin thinking about how to create a bomb, not whether it was possible. As enemy aliens, Frisch and Peierls were initially excluded from the MAUD Committee, but the absurdity of this was soon recognised, and they were made members of its Technical Subcommittee. This did not mean that they were cleared for radar work. When Oliphant made the services of his secretary available for typing up the Peierl's and Frisch's papers for the MAUD Committee in September 1940, they were not allowed to enter the Nuffield Building where she worked, so Peierls submitted them for typing by dictaphone on wax cylinders. Frisch and Peierls thought at first that uranium enrichment was best achieved through thermal diffusion, but as the difficulties with this approach became more apparent they switched to gaseous diffusion, bringing in a fellow refugee from Germany, Franz Simon, as an expert on the subject. Peierls also recruited yet another refugee from Germany, Klaus Fuchs, as his assistant in May 1941. Manhattan Project As a result of the MAUD Committee's findings, a new directorate known as Tube Alloys was created to coordinate the nuclear weapons development effort. Sir John Anderson, the Lord President of the Council, became the minister responsible, and Wallace Akers from Imperial Chemical Industries (ICI) was appointed the director of Tube Alloys. Peierls, Chadwick and Simon were appointed to its Technical Committee, which was chaired by Akers. Its first meeting, in November 1941, was attended by two American