PEACEKEEPER MISSILE

, also called Mx, U.S. intercontinental ballistic missile (ICBM) that entered service in 1986. Under development from 1971, the MX (for missile experimental) evolved into a 71-foot (22-metre) ICBM with a bus, or fourth stage, located in its front end that carried 10 or 12 independently targetable thermonuclear warheads. This endowed each missile with several times the firepower of the two- or three-warhead Minuteman III, which it was designed to replace. In addition, the MX's extremely accurate guidancean inertial system capable of being updated in flight by signals from navigation satellitesgave its 300-kiloton warheads greater potential to destroy reinforced missile silos and command bunkers in the Soviet Union. The MX had a range of approximately 7,000 miles (11,000 km). In order to be able to evade attack by Soviet ICBMs, which lagged behind U.S. ICBMs in accuracy but were far more powerful, several types of bases for the MX were proposed. These included launching by air from huge transport jets, deep basing in silos located more than 1,000 feet (305 m) underground, shuttling the missiles continuously on trucks or rail cars among multiple protective shelters, and grouping silos close together in a dense pack, so that incoming nuclear warheads would destroy or deflect one another. All of these modes proved to be prohibitively expensive, and none was politically popular; in 1983 it was decided to place the missiles in Minuteman III silos. Although plans called for 100 Peacekeepers, only 50 were authorized for deployment at Warren Air Force Base, Wyoming.