A comprehensive American program of research on plutonium and 235U isotope separation evolved between mid-1941 and mid-1942. Plans were formulated for the construction of plutonium production reactors, uranium separation plants, and centralized bomb research facilities. The program for producing 235U by gaseous diffusion was slowed both by the technical problem of finding a suitable isotope separation filter, or “barrier,” and by the difficulty of coordinating Kellogg Company employees and Columbia University researchers. Despite such obstacles, plans for providing fissionable materials were well on the way to being implemented by 1943.

Expansion of the American Atomic Bomb Program

In June 1941, Vannevar Bush persuaded President Roosevelt to form the Office of Scientific Research and Development (OSRD), under the aegis of the Office of Emergency Management. With Bush as director, the OSRD assumed responsibility for mobilizing scientific resources and applying research to national defense. James Conant replaced Bush as chairman of the National Defense Research Committee, which now operated as a unit of the OSRD. Recommendations for research contracts were channeled through Conant and placed by Bush. The Advisory Committee on Uranium, essentially a research organization, became the S-1 Section of OSRD and remained in place throughout the war. Bush and Conant established three subsections of S-1: one on theoretical research under Fermi; one on power production under George Pegram, physicist and dean of the graduate faculties at Columbia University; and a third on heavy water and isotope separation under Columbia chemist Harold Urey.