Atomic Bomb

Atomic bombs were the first nuclear weapons to be developed, tested, and used. In the late 1930s physicists in Europe and the United States realized that the fission of uranium could be used to create an extremely powerful explosive weapon. In August 1939, German American physicist Albert Einstein sent a letter to U.S. president Franklin D. Roosevelt that described this discovery and warned of its potential development by other nations. The U.S. government established the top secret Manhattan Project in 1942 to develop an atomic device. The leader of the Manhattan Project was U.S. Army Brigadier General Leslie R. Groves. His team, working in several locations but in large part at Los Alamos, New Mexico, under the direction of American physicist J. Robert Oppenheimer, designed and built the first atomic bombs.

The first atomic explosion was conducted, as a test, at Alamogordo, New Mexico, on July 16, 1945. The energy released from this explosion was equivalent to that released by the detonation of 20,000 tons of TNT. Near the end of World War II, on August 6, 1945, the United States dropped the first atomic bomb on the Japanese city of Hiroshima. It followed with a second bomb against the city of Nagasaki on August 9. According to U.S. estimates, 60,000 to 70,000 people were killed by the Hiroshima bomb, called "Little Boy," and about 40,000 by the bomb dropped on Nagasaki, called "Fat Man." Japan agreed to Allied terms of surrender on August 14th. These are the only times that a nuclear weapon has been used in a conflict between nations.

Fusion bombs, also called hydrogen or thermonuclear bombs, were developed and tested in the early 1950s, but these have never been used in warfare. A thermonuclear device depends on a fission reaction to produce extreme heat that causes hydrogen isotopes of deuterium and tritium to come together, or fuse, but the main energy source for thermonuclear devices comes from the fusion reaction, not the triggering fission reaction. For more information on this type of bomb, see Hydrogen Bomb.

Several nations have exploded nuclear devices in tests in the atmosphere, under the earth, and under the sea. Only the United States, Russia, the United Kingdom, France, China, India, and Pakistan admit to possessing nuclear weapons. South Africa admitted to having built and then dismantling a number of bombs. Other nations, however, including Israel, are thought to have