| I Nuclear Weapons
explosive devices designed to release nuclear energy on a large scale, used primarily in military applications. The first atomic bomb (or A-bomb), which was tested on July 16, 1945, at Alamogordo, New Mexico, represented a completely new type of explosive. All explosives prior to that time derived their power from the rapid burning or decomposition of some chemical compound. Such chemical processes release only the energy of the outermost electrons in the atom. Nuclear explosives, on the other hand, involve energy sources within the core, or nucleus, of the atom. The A-bomb gained its power from the splitting, or fission, of all the atomic nuclei in several kilograms of plutonium. A sphere about the size of a baseball produced an explosion equal to 20,000 tons of TNT. The A-bomb was developed, constructed, and tested by the Manhattan Project, a massive United States enterprise that was established in August 1942, during World War II. Many prominent American scientists, including the physicists Enrico Fermi and J. Robert Oppenheimer and the chemist Harold Urey, were associated with the project, which was headed by a U.S. Army engineer, then-Brigadier General Leslie R. Groves. After the war, the U.S. Atomic Energy Commission became responsible for the oversight of all nuclear matters, including research on hydrogen bombs. In these bombs the source of energy is the fusion process, in which nuclei of the isotopes of hydrogen combine to form a heavier helium nucleus (see Thermonuclear, or Fusion, Weapons below). This weapons research resulted in the production of bombs that range in power from a fraction of a kiloton (1,000 tons of TNT equivalent) to many megatons (1 megaton equals 1 million tons of TNT equivalent). Furthermore, the physical size of a nuclear bomb was drastically reduced, permitting the development of nuclear artillery shells and small missiles that can be fired from portable launchers in the field. Although nuclear bombs were originally developed as strategic weapons to be carried by large bombers, nuclear weapons are now available for a variety of both strategic and tactical applications. Not only can they be delivered by different types of aircraft, but rockets and guided missiles of many sizes can now carry nuclear warheads and can be launched from the ground, the air, or underwater. Large rockets can carry multiple warheads for delivery to separate targets. |