MILITARY
MISSILES From these beginnings grew the immense challenge of the postwar era. As tension developed between the USSR
and the Western Allies, the demand for weapons of even greater power increased. In little more than a decade missiles that at best could carry chemical explosives a few hundred kilometers were superseded by multistage ballistic missiles capable of lobbing thermonuclear warheads into the heart of another continent. These gave rise to the antiballistic missile and also focused attention on the merits of short-range tactical missiles. The term ballistic missile derives from the ballistic path the missiles follow after the initial propulsion phase (see ballistics). They usually make use of the multistage principle, a major breakthrough in rocket technology. The multistage rocket consists of two or more rockets mounted parallel or in tandem. The first rocket carries the upper stages to a certain altitude and separates when its propellants are exhausted. The next stage fires and lifts the remaining stage or stages still higher. The final speed attained by the last stage is equal to the sum of the net changes in velocity accomplished by each stage. In this way unnecessary structure is discarded as soon as it is no longer accelerating the vehicle, and the payload can attain the high speeds necessary to reach a distant target. Any long- or short-range missile equipped with a
guidance and control system is called a guided missile. To achieve accuracy, ballistic missiles usually depend on inertial guidance systems using precision gyroscopes and other devices that sense deviations from a preset flight path and restore the vehicle to that path, usually by swiveling the engines to produce offset thrust. Because this type of guidance system does not give out a signal, it cannot be jammed by radio waves. Once engine thrust is terminated by the guidance system, the vehicle follows a ballistic path like an artillery shell, usually without further power or guidance. The guidance systems of tactical missiles may be either external or internal. External guidance, which is effective only over short ranges, makes use of a homing system or of a light beam or radar beam, aimed at the target, that the missile follows. Internal guidance, however, does not permit control of the trajectory after the missile has been
launched. Such a guidance system may consist, for example, of an electronic memory storing a preprogrammed course. Ballistic missiles that are launched from land include the intercontinental ballistic missile (ICBM), with a range exceeding 8,000 km (5,000 mi); the intermediate-range ballistic missile (IRBM), with a range between 2,500 and 8,000 km (1,500 and 5,000 mi); the medium-range ballistic missile (MRBM), with a range between 800 and 2,500 km (500 and 1,500 mi); and the short-range ballistic missile (SRBM), with a range up to 800 km (500 mi). ICBM development was spurred in 1954 by the development of the hydrogen bomb and by reductions in the dimensions of atomic bombs, which made possible warheads that could be carried by missiles. The first U.S. ICBMs successfully launched were the Atlas (1958), the Titan (1959), and the Minuteman I (1961). These were followed by Minuteman II (1965) and Minuteman III (1970), which together with Titan II make up the land-based U.S. strategic nuclear force. Development of the MX missile, or Peacekeeper, a 10-warhead ICBM, began in 1979. The United States began to develop the submarine-launched ballistic missile (SLBM) in 1954, the same year that the first nuclear submarine, the Nautilus, was launched. Under the Fleet Ballistic Missile (FBM) Program, 41 submarines had been built by 1968, each armed with 16 Polaris missiles. The last version was Polaris A3, with a range of 4,600 km (2,800 mi). The Poseidon SLBM, the development of which began in 1964, was twice as heavy as the Polaris A3 and had twice its payload capacity. The approaching end of the Poseidon development program and the strategic demand for an SLBM with a range of more than 6,400 km (4,000 mi) led to the initiation of the Trident program in 1975. Only the Trident remains in production. A Soviet submarine, armed with 16 missiles comparable in range to the Polaris A1, became operational only in 1966. An effort comparable to the FBM Program began in the USSR in 1970. The military significance of the SLBMs lies in their near-invulnerability when the submarines carrying them are submerged (see nuclear strategy). A system for the use of multiple warheads on a single missile first became operational in 1964. At the end of 1967 the multiple independently targeted reentry vehicle (MIRV) concept was originated, whereby multiple warheads are independently targeted near the end of the ballistic missile flight (see MIRVed missile). A further refinement was the installation of a homing system in the MIRV warhead for navigation and target recognition. A maneuvering reentry vehicle (MARV), utilizing radar scanning devices and a computerized guidance system, has been developed to deliver multiple nuclear warheads with pinpoint accuracy. The MIRV has the advantage of increasing the possibility of penetrating an antiballistic missile system and therefore is more lethal.