Project, thought Oppenheimer too important to the project to be ousted over this suspicious behavior. On July 20, 1943, he wrote to the Manhattan Engineer District: Manhattan Project Los Alamos On October 9, 1941, two months before the United States entered World War II, President Franklin D. Roosevelt approved a crash program to develop an atomic bomb. In May 1942, National Defense Research Committee Chairman James B. Conant, who had been one of Oppenheimer's lecturers at Harvard, invited Oppenheimer to take over work on fast neutron calculations, a task Oppenheimer threw himself into with full vigor. He was given the title "Coordinator of Rapid Rupture", which specifically referred to the propagation of a fast neutron chain reaction in an atomic bomb. One of his first acts was to host a summer school for bomb theory at his building in Berkeley. The mix of European physicists and his own students—a group including Robert Serber, Emil Konopinski, Felix Bloch, Hans Bethe and Edward Teller—kept themselves busy by calculating what needed to be done, and in what order, to make the bomb. In June 1942, the US Army established the Manhattan Project to handle its part in the atom bomb project and began the process of transferring responsibility from the Office of Scientific Research and Development to the military. In September, Groves was appointed director of what became known as the Manhattan Project. He selected Oppenheimer to head the project's secret weapons laboratory. This choice surprised many, because Oppenheimer had left-wing political views and no record as a leader of large projects. Groves was concerned by the fact that Oppenheimer did not have a Nobel Prize and might not have had the prestige to direct fellow scientists. But he was impressed by Oppenheimer's singular grasp of the practical aspects of designing and constructing an atomic bomb and by the breadth of his knowledge. As a military engineer, Groves knew that this would be vital in an interdisciplinary project that would involve not just physics, but chemistry, metallurgy, ordnance and engineering. Groves also detected in Oppenheimer something that many others did not, an "overweening ambition" that Groves reckoned would supply the drive necessary to push the project to a successful conclusion. Isidor Rabi considered the appointment "a real stroke of genius on the part of General Groves, who was not generally considered to be a genius". Oppenheimer and Groves decided that for security and