ABM system: see anti-ballistic missile system.

anti-ballistic missile system: a system, typically ground-based, that includes radars and nuclear and nonnuclear missiles theoretically capable of detecting, tracking, and destroying incoming offensive missiles.

anti-satellite systems: technologies oriented toward destroying satellites used in intelligence-gathering or possibly in actual fighting.

ASAT: see anti-satellite systems.

ballistic missile: a missile characterized by a free-falling trajectory heavily influenced by gravity. Classified on the basis of range (short-range, intermediate, and intercontinental), it may be land- or sea-launched. See also intercontinental ballistic missile, submarine-launched ballistic missile, and multiple independently targetable re-entry vehicle.

ballistic missile defense: space-based or ground-based anti-ballistic missile systems. The term is used interchangeably with anti-ballistic missile defense system (q.v.) and is now viewed as the central focus of the Strategic Defense Initiative (q.v.).

BMD: see ballistic missile defense.

counterforce weapons: nuclear weapons directed toward an opponent's military personnel and installations.

countervalue weapons: nuclear weapons targeted toward an opponent's civilian population or industry.

deterrence: a theory of conflict management in which an opponent is "dissuaded" from initiating an attack by the threat of unacceptable retaliation. See mutual assured destruction.

fission: a process in which the nucleus of a heavy atom splits into lighter nuclei, thereby releasing vast amounts of energy. Atomic bombs rely on the fission of uranium or plutonium. Also, all fusion (hydrogen or thermonuclear) weapons use a fission weapon to trigger them. (See fusion.) Fission reactions release much more energy than conventional explosions.

fusion: a process in which light atoms are combined to form a heavier atom and in the process release vast amounts of energy. Hydrogen and thermonuclear bombs rely on a fusion reaction initiated by a fission weapon. (See fission.) Fusion reactions release much more energy than fission reactions.

horizontal proliferation: the spread of nuclear weapons to non-nuclear nations.

ICBM: see intercontinental ballistic missile.

intercontinental ballistic missile: a ground-based missile having a range of at least 5,500 kilometers; each ICBM can carry several warheads. See also ballistic missile; multiple independently targetable re-entry vehicle; submarine-launched ballistic missile; Triad.

kiloton: a measure of the yield of a nuclear weapon. It is equivalent to 1,000 tons of TNT. Many early nuclear weapons, including those used in Hiroshima and Nagasaki, were of this size. Today, weapons of this yield are primarily characterized as tactical or battlefield weapons. See also megaton and tactical weapons.

MAD: see Mutual Assured Destruction.

megaton: a measure of the yield of nuclear weapons. It is equivalent to one million tons of TNT, or a thousand times the yield of a kiloton (q.v.). A megaton is typically the unit for measuring the yield of strategic, as opposed to tactical, nuclear weapons.

MIRV: see multiple independently targetable re-entry vehicle.

multiple independently targetable re-entry vehicle (MIRV): a system in which two or more nuclear warheads carried by a single ballistic missile are capable of being delivered to different targets. See also ballistic missile; intercontinental ballistic missile; submarine-launched ballistic missile.

mutual assured destruction (MAD): a theorized capacity of both the United States and [former] U.S.S.R. to inflict "unacceptable" damage on the other after suffering a nuclear attack.

SDI: see Strategic Defense Initiative.

SLBM: see submarine-launched ballistic missile.

Strategic Defense Initiative: the proposed development of a space- and land-based system of defense against strategic nuclear weapons. SDI remains a theoretical possibility rather than an existing technological reality. See also anti-ballistic missile system; anti-satellite systems; ballistic missile defense.

strategic weapons: weapons/forces that can affect an opponent's warring ability.

submarine-launched ballistic missile: the sea-based leg of the three primary means of delivering nuclear weapons. See also ballistic missile; intercontinental ballistic missile; multiple independently targetable re-entry vehicle; Triad.

tactical weapons: weapons/forces for combat with an opponent.

thermonuclear weapon: a nuclear weapon in which thermonuclear fusion reactions create the explosive energy released. Hydrogen bombs are thermonuclear weapons. See fission; fusion.

Triad: the tripartite division of nuclear weapon delivery systems, including land-based intercontinental ballistic missile (q.v.), submarine-launched ballistic missiles (q.v.), and bombers.

vertical proliferation: the increase in the numbers of nuclear weapons systems by nuclear nations. See also horizontal proliferation.