Famous physicists and scientists like Ernest Rutherford and Albert Einstein knew there were huge amounts of energy inside of atoms, but didn’t have any way to release it. Things started to change quickly starting in the 1930s. In 1932, Sir John Cockcroft and Ernest Walton were able to cause a nuclear reaction for the first time by artificially accelerated particles, and then in 1934, Irene Curie, Frederic Curie, and Enrico Fermi separately made artificial radioactivity by colliding atoms with alpha particles and neutrons. Coupled with the possibility of a chain reaction for a tremendous amount of energy release, people began to realize that nuclear fission could be used as a powerful weapon.
C. Peter Chen 2004 / US history.org march 2014
On August 2nd 1939, a Hungarian Jewish refugee in the United States Leo Szilard wrote a letter with Albert Einstein, urging President Franklin Roosevelt to start funding for atomic research so that they could apply the research as a weapon. (Gene Dannon 1996) The letter reached Roosevelt's desk in September, who agreed with the scientists cry for help, and authorized the creation of the Uranium Committee under Lyman Briggs, which began research programs at the Naval Research Lab in Washington D.C. in 1939. In 1940, the Uranium Committee was absorbed into the larger National Defense Research Committee. Progress was slow, because of the low sense of urgency as the United States had not entered the war yet.
US history.org march 2014
Meanwhile, scientists in Britain also started on a similar mission. In March 1940, at the University of Birmingham, research done by Otto Frisch and Rudolf Peierls eventually led to the Scientific Survey of Air Warfare's finding that an uranium bomb could be produced using only 25 pounds of uranium235, which was a workable size for a weapon. This was something that the leading German physicists for the Nazi’s atomic weapon research program, never achieved. The friendliness between Britain and the United States allowed this new finding to be shared between the two nations, but Lyman Briggs made no effort of sharing this information with his physicists. Briggs' failure then led to the atomic weapon research program to be transferred directly under NDRC's chief Vannevar Bush, in Nov 1941. Briefly, the headquarters of the research project was located at 90 Church Street in Manhattan in New York City. Although it was soon moved, the name Manhattan remained with the project.
William J. Broad October 2007
When the United States entered the war in December 1941, research efforts accelerated. In early 1942, University of Chicago Metals Lab joined in to study plutonium (which had just been discovered by Glenn Seaborg in Feb 1941) while physicist J. Robert Oppenheimer of the University of California at Berkeley took over the research for calculations that had to do with the weapon detonation. John Manley was assigned to help Oppenheimer with his research efforts of over...