Antiaircraft Weapons, weapons designed to destroy aircraft in flight. They can be surface-to-air weapons, fired from ground positions or naval vessels; or air-to-air weapons, fired from aircraft.

Surface-to-air Weapons
Antiaircraft Guns

During World War II and the Korean War (1950-53), the most important surface-to-air weapons for destroying enemy aircraft were antiaircraft guns. Antiaircraft (AA) guns differ from field artillery weapons in that they are mounted so they can fire skyward and are equipped with devices for speedy aiming and firing at fast-moving targets. The terms "flak" and "ack-ack" are used to designate both AA guns and the bursting shells fired from them.

Antiaircraft ammunition may have a fuze that causes the shell to explode at a certain height, or it may carry a proximity fuze, a fuze containing a tiny radio transmitter-receiver that automatically explodes the shell when it gets close to the target.

The AA guns used in World War I were modified field-artillery weapons, and were not very effective. During World War II, cities were defended by AA guns, searchlights, radar, and barrage balloons (elongated balloons anchored by numerous cables that, if struck, could disable enemy planes).

The 90-mm AA gun used by the U.S. Army during World War II could fire a 23-pound (10-kg) projectile to a height of six miles (10 km). The Browning .50-caliber machine gun, which can be mounted almost any place, was highly effective against low-flying aircraft during that war.

Large-caliber guns, such as the U.S. Army's 75-mm and 90-mm AA weapons, were replaced with missiles during the 1960's and 1970's. The last notable use of large AA guns was in the Vietnamese War (1957-75), when guns of calibers up to 100 mm were used by the North Vietnamese against American aircraft.

Widely used in most major armies for protection against low-flying aircraft are light AA guns-rapid-fire 20- to 25-mm cannon. They are usually mounted on armored vehicles. The U.S. Army uses the Vulcan Air Defense System, consisting of a six-barrel 20-mm automatic cannon mounted on an armored vehicle.

Missiles

During the 1950's, surface-to-air missiles (SAM's) were developed by the United States and other nations. Soviet-built SAM's were used against American planes in Vietnam.

The U.S. Army and other NATO forces are equipped with Patriot and Hawk missiles for air defense. The Patriot, adopted in the early 1980's, is designed for defense against both aircraft and missiles. Its range is about 42 miles (68 km). The Hawk, adopted in the early 1960's, is designed as a medium- to low-altitude missile, and can hit planes flying at treetop level. Its maximum range is about 25 miles (40 km).

The U.S. Army also uses the Chaparral, a surface-to-air missile that is a modification of the Sidewinder, an air-to-air missile. The Chaparral has a range of about three miles (4,800 m).

From the early 1950's to the early 1960's, many large cities and military installations in the United States were protected by batteries of surface-to-air missiles. These were intended as a defense against long-range bombers. Such batteries were removed in the late 1960's, after intercontinental ballistic missiles (ICBM's) replaced bombers as the main enemy threat.

In the early 1980's, the U.S. Army and U.S. Marine Corps adopted the Stinger, a portable, short-range, shoulder-fired missile, for use against low-flying aircraft.

Air-to-air Weapons

Machine guns, which fire bullets in rapid succession, were the standard air-to-air weapons during World Wars I and II, although single-barrel and multibarrel cannon, which fire explosive shells, appeared on some planes during the latter war. Some post-World War II aircraft machine guns fired explosive-type bullets. In the Korean War, jet planes used machine guns and automatic cannon for air-to-air combat. Since then, cannon have replaced machine guns. Aircraft cannon generally have calibers of 20 mm and 30 mm.

Air-to-air rockets were first used during World War II. Development of air-to-air missiles began late in that war, and by 1953 operational missiles were available. Both missiles and rockets contain explosive warheads and are self-propelled; the flight path of a missile, however, can be changed (by radio signals, for example) after firing, whereas that of a rocket cannot. All rockets—and many types of missiles—are propelled through the air by reaction from the rearward discharge of burning gases.

Some air-to-air missiles, such as the Sidewinder, are heat-seeking. Others, such as the Sparrow and Phoenix, use radar guidance for homing in on a target.