ICBM

ICBM, acronym for intercontinental ballistic missile, a rocket designed to carry nuclear warheads thousands of kilometers to their targets. ICBMs are the largest class of guided missiles. An ICBM typically has two or three stages that propel it high into the atmosphere, where it then follows a free-fall path, or ballistic trajectory, toward its target. Early ICBMs could carry only one nuclear warhead apiece, but modern ICBMs can easily carry several individual warheads. ICBMs are launched either from protected underground launching tubes called silos or from mobile missile launchers, which may be mounted on trucks or railroad cars. ICBMs were built to deliver nuclear bombs faster than bomber aircraft, which can be shot down, and without risking the lives of bomber crews. The primary purpose of an ICBM fleet is to destroy the enemy homeland and missile fleet, but the secondary, and more important, purpose is to deter war by making it so horrible that no nation will undertake it for fear of retaliation (see Deterrence).

The United States and Russia maintain the largest fleets of ICBMs. The newest U.S. ICBM is the LGM-118 Peacekeeper, originally known as the MX. The Peacekeeper has three solid-fueled stages, topped by a small liquid-fueled stage called a post-boost vehicle. This top stage carries several individual nuclear warheads called multiple independently targeted reentry vehicles, or MIRVs. Each MIRV can produce an explosion equivalent to 450,000 tons of TNT. An internal mechanism known as an inertial guidance system keeps the Peacekeeper on target over ranges of almost 11,000 km (7,000 mi). The Peacekeeper is 21.6 m (71 ft) long, 2.2 m (7 ft 8 in) in diameter, and weighs 88,500 kg (195,000 lb).

The forerunner of the ICBM was the V-2 rocket, which was developed in Germany during World War II (1939-1945) by a team led by Wernher von Braun. The governments of both the United States and the Soviet Union recognized the importance of rocket technology, and both governments used captured German scientists, equipment, and data in their rocket programs after World War II.

The United States and the Soviet Union began experimenting with large and small rockets for both scientific and military uses. The Soviet Union had the greatest early success, and its launching of the first artificial satellite, Sputnik 1, in October 1957 demonstrated that long-range ballistic missiles were practical. The United States sped up efforts to develop intercontinental missiles of its own. U.S. Air Force General Bernard Schriever led a team that fielded the first successful U.S. ballistic missile, the Atlas, in 1958. The Titan, Titan II, and Minuteman series quickly followed the Atlas, all within an eight-year period.

The United States and the Soviet Union continued to improve their ICBM fleets, producing missiles with longer ranges, better accuracy, and the capability of carrying heavier loads. Arms control treaties such as START II, ratified by the U.S. Senate in 1996, have led to general reductions in ICBM fleets and in the number of warheads each missile may carry. ICBMs still remain a powerful deterrent to nuclear attack, and many nations continue research and development on long-range missiles.

See also Defense Systems; Cold War; Arms Control; SLBM.