NUCLEAR WEAPON

also called atomic weapon, or thermonuclear weapon bomb or other warhead that derives its force from either the fission or the fusion of atomic nuclei and is delivered by an aircraft, missile, Earth satellite, or other strategic delivery system. Nuclear weapons have enormous explosive force. Their significance may best be appreciated by the coining of the words kiloton (1,000 tons) and megaton (one million tons) to describe their blast effect in equivalent weights of TNT. For example, the first nuclear fission bomb, the one dropped on Hiroshima, Japan, in 1945, released energy equaling 15,000 tons (15 kilotons) of chemical explosive from less than 130 pounds (60 kilograms) of uranium. Fusion bombs, on the other hand, have given yields up to almost 60 megatons. The first nuclear weapons were bombs delivered by aircraft; warheads for strategic ballistic missiles, however, have become by far the most important nuclear weapons. There are also smaller tactical nuclear weapons that include artillery projectiles, demolition munitions (land mines), antisubmarine depth bombs, torpedoes, and short-range ballistic and cruise missiles. The U.S. stockpile of nuclear weapons reached its peak in 1967 with more than 32,000 warheads of 30 different types; the Soviet stockpile reached its peak of about 33,000 warheads in 1988. also called Atomic Weapon, or Thermonuclear Weapon, bomb or other warhead that derives its force from either the fission or the fusion of atomic nuclei and is delivered by an aircraft, missile, Earth satellite, or other strategic delivery system. Nuclear weapons are the most potent explosive devices yet invented and may be deployed in such delivery systems as missiles and even artillery shells. They derive their destructive force from energy contained in the core, or nucleus, of atoms. This energy may be explosively released in two types of nuclear reactions: fission, in which heavy-element nuclei break down into fragments (which actually constitute lighter elements), and fusion, in which the nuclei of the lightest element (hydrogen) are squeezed together at high temperatures and fuse to form helium nuclei. Nuclear weapons are accordingly classified as fission (or atomic) or fusion (hydrogen, or thermonuclear) bombs. Additional reading The history of nuclear weapons is the subject of voluminous literature. Richard Rhodes, The Making of the Atomic Bomb (1986), is an excellent work on the U.S. effort to develop nuclear weapons. It can be supplemented by the official histories: Vincent C. Jones, Manhattan, the Army and the Atomic Bomb (1985); David Hawkins, Edith C. Truslow, and Ralph Carlisle Smith, Manhattan District History-Project Y, the Los Alamos Project, 2 vol. (1961, reprinted as Project Y, the Los Alamos Story, in 1 vol. with a new introduction, 1983); and Richard G. Hewlett, Oscar E. Anderson, Jr., and Francis Duncan, A History of the United States Atomic Energy Commission, 2 vol. (196269); continued by Richard G. Hewlett and Jack M. Hall, Atoms for Peace and War, 19531961 (1989). For the development of thermonuclear weapons, see Herbert F. York, The Advisors: Oppenheimer, Teller, and the Superbomb (1976); and Hans A. Bethe, Comments on the History of the H-Bomb, Los Alamos Science, 3(3):4353 (Fall 1982). Technical data are compiled in Thomas B. Cochran, William M. Arkin, and Milton M. Hoenig, U.S. Nuclear Forces and Capabilities (1984); and Thomas B. Cochran et al., U.S. Nuclear Warhead Production (1987), and U.S. Nuclear Warhead Facility Profiles (1987).The British project is discussed in the official histories of the U.K. Atomic Energy Authority: Margaret Gowing, Britain and Atomic Energy, 19391945 (1964), and Independence and Deterrence: Britain and Atomic Energy, 19451952, 2 vol. (1974). Little has been published about the program of the former U.S.S.R., but see David Holloway, The Soviet Union and the Arms Race, 2nd ed. (1984); and Thomas B. Cochran, Soviet Nuclear Weapons (1989). No official history is available for the French project. Bertrand Goldschmidt, Les Rivalits atomiques, 19391966 (1967), is a semiofficial account by a participant. The Chinese project is covered in John Wilson Lewis and Xue Litai, China Builds the Bomb (1988). David Irving, The German Atomic Bomb (1968, reprinted 1983), covers the German program; and Robert K. Wilcox, Japan's Secret War (1985), examines Japanese work on the atomic bomb. Proliferation developments are followed in Leonard S. Spector, Nuclear Proliferation Today (1984), The New Nuclear Nations (1985), Going Nuclear (1987), and The Undeclared Bomb (1988). Thomas B. Cochran Robert S. Norris