In May 1941, Urey was appointed to the Committee on Uranium, which oversaw the uranium project as part of the National Defense Research Committee (NDRC). In 1941, Urey and George B. Pegram led a diplomatic mission to England to establish co-operation on development of the atomic bomb. The British were optimistic about gaseous diffusion, but it was clear that both gaseous and centrifugal methods faced formidable technical obstacles. In May 1943, as the Manhattan Project gained momentum. Urey became head of the wartime Substitute Alloy Materials Laboratories (SAM Laboratories) at Columbia, which was responsible for the heavy water and all the isotope enrichment processes except Ernest Lawrence's electromagnetic process.