In April 1940, Jesse Beams, Ross Gunn, Fermi, Nier, Merle Tuve and Harold Urey had a meeting at the American Physical Society in Washington, D.C. At the time, the prospect of building an atomic bomb seemed dim, and even creating a chain reaction would likely require enriched uranium. They therefore recommended that research be conducted with the aim of developing the means to separate kilogram amounts of uranium-235. At a lunch on 21 May 1940, George B. Kistiakowsky suggested the possibility of using gaseous diffusion.