Atomic bomb

   The atomic bomb was a weapon made using enriched uranium, which on detonation caused a chain nuclear reaction involving the fission of atomic particles. Development of the atomic bomb in the United States began after Albert Einstein wrote to Franklin D. Roosevelt in August 1939 informing him of the early discoveries in atomic science and the potential to create a powerful bomb based on nuclear fission and warning of the need to develop such weaponry before Nazi Germany. In 1942, the government established the Manhattan Project under the leadership of General Leslie R. Groves, and on 16 July 1945 the first bomb was tested in Alamogordo, New Mexico. The first bomb was used during World War II when it was dropped on Hiroshima, Japan, on 6 August 1945. A second bomb was dropped on 9 August on Nagasaki. Both bombs had devastating effects, and shortly afterward proposals were drawn up in an effort to prevent the proliferation of atomic weapons.

   These proposals were put to the United Nations in the Baruch Plan but were rejected by the Soviet Union. With the onset of the Cold War and the testing of an A-bomb by the Soviet Union in 1949, the threat of nuclear war became a real possibility. In 1952, the atomic bomb was superseded by the hydrogen bomb, a more powerful weapon based on nuclear fusion rather than fission.

   See also Atomic Energy Act.