Notes

On October 11, 1939, President Franklin D. Roosevelt received a letter from Albert Einstein, which Einstein had actually written on August 2, 1939. The letter told of a new field of physics that was showing that the element uranium could undergo nuclear fission, with the resultant release of a great deal of energy. Einstein described the probability that a sustained nuclear reaction could be produced and the possibility of the construction of extremely powerful bombs. He described the possibility that such bombs could be delivered by ship, although he was skeptical that such weapons could be delivered by air. He noted the likelihood that Germany would pursue the same line of research and that the Germans had already suspended the export of uranium from the Czech mines in their newly acquired territory.

Roosevelt took the warning seriously, and within a month had organized a research committee. The United States introduced its own nuclear program under the Army Corps of Engineers in June 1942. The U.S. needed to build an atomic weapon before Germany or Japan did.