self-propelled, unmanned space or air vehicle carrying an explosive warhead. Its path can be adjusted during flight, either by automatic self-contained controls or remote human control. Guided missiles are powered either by rocket engines or by jet propulsion. The American, R. H. Goddard, did important early work on rockets, but guided missiles were first developed in their military form by the Germans, who in World War II employed V-1 and V-2 missiles against Great Britain and the Low Countries. The V-1 was the first cruise missile; it was powered through most of its flight and followed a straight-line trajectory to its target. The V-2, which was powered only during the first part of its flight, was the world's first operational ballistic missile, with a powered launch followed by an unpowered parabolic trajectory, sometimes guided by radio. Such missiles have since become the key strategic weapon of modern warfare and a crucial, and much used, tactical weapon.
Guided missiles are of various types and ranges. Missiles may be aerodynamic, i.e., controlled by aerodynamic surfaces and following a straight-line trajectory to the target, or ballistic, i.e., powered during flight and following a parabolic trajectory. Long-range missiles generally have nuclear warheads, while short-range missiles usually have high-explosive warheads.
Aerodynamic missiles are of four types. Air-to-air missiles are fired by aircraft at enemy aircraft and are often guided by self-contained controls that detect and target the missile toward heat sources. Surface-to-air missiles, such as the U.S. Patriot missile and Israeli Iron Dome system missiles, operate against aircraft or other missiles. Both types may supplement antiaircraft guns. Air-to-surface missiles, launched by aircraft against ground positions, are generally radio-controlled. Surface-to-surface missiles (including ship and submarine launched versions) include many different types, such as antitank weapons. Longer-range surface-to-surface missiles, such as the Iraqi Scud, are in fact short-range ballistic missiles. Cruise missiles, which are launched like a missile but use flipout wings and a turbofan engine to fly like an airplane to the target at altitudes of about 50 ft (15 m), are either air-to-surface or surface-to-surface missiles.
All long-range missiles are ballistic. The intermediate-range ballistic missile (IRBM) can reach targets up to 1,500 nautical miles away, while the intercontinental ballistic missile (ICBM) has a range of many thousands of miles. The first operational U.S. ICBM, the Atlas D, was controlled by radio, but since then inertial guidance, which uses internal gyroscopes to calculate and correct direction (sometimes with celestial, and then terrestrial readings), has been used. The key U.S. offensive ballistic missiles are the Minutemen ICBMs, which are launched from silos, and the submarine-launched Tridents, which replaced the earlier Polaris and Poseidon. All currently deployed ballistic missiles can be equipped with Multiple Independently Targetable Reentry Vehicles (MIRVs), which permit one booster to carry several warheads, each guided to a separate target. An antiballistic missile (ABM) is designed to detect and intercept enemy ballistic missiles. Space-, air-, sea-, and mobile land-based ABMs were barred by the 1972 ABM treaty, but the United States announced its withdrawal from that agreement in 2001.
The Soviet Union completed the first operative ICBMs in 1958, and the United States, reacting to a supposed “missile gap,” gained overwhelming missile superiority by 1962, which in terms of accuracy and payload it never relinquished. Offensive and defensive ballistic missiles have been regulated by a number of arms control agreements between the United States and the USSR/Russia (see disarmament, nuclear). Military ballistic missiles have been used as launchers for civilian space projects (see space exploration).