The primary objective of the Manhattan Project during World War II was the creation of a nuclear fission or atomic bomb. Even before that goal was accomplished in 1945, however, some nuclear scientists were thinking about the next step in the development of nuclear weapons, a fusion or hydrogen bomb.

Progress on a fusion bomb was slow. Questions were raised about the technical possibility of making such a bomb, as well as the moral issues raised by the use of such a destructive weapon. But the detonation of an atomic bomb by the Soviet Union in 1949 placed the fusion bomb in a new perspective. Concerned that the United States was falling behind in its arms race with the Soviet Union, President Harry S. Truman authorized a full-scale program for the development of a fusion weapon.

The first test of a fusion device occurred on October 31, 1952, at Eniwetok...