Robert S. Norris: By the late 30s, physicists, in Europe primarily, but some in America too, were making great discoveries about the atom. The key date here was January 1939, when European scientists had discovered fission. News of that was brought to the United States by Niels Bohr. Actually, it was brought to Washington, DC, at a conference at George Washington University.
Charles Critchfield was a mathematical physicist assigned to work on the development of gun-type fission weapons, and eventually implosion-type weapons, at Los Alamos. He returned to Los Alamos in 1952 to work on the development of the hydrogen bomb.
[We would like to thank Robert S. Norris, author of the definitive biography of General Leslie R. Groves, Racing for the Bomb: General Leslie R. Groves, the Manhattan Project's Indispensable Man, for taking the time to read over these transcripts for misspellings and other errors.]