Artillery piece fired from the ground or shipboard in defense against aerial attack.
They were first used in combat in World War I, when field artillery were converted to antiaircraft use by mountings that enabled them to fire nearly vertically. Range finders and searchlights, developed in the 1920s and '30s, increased their effectiveness. Advances in World War II included rapid-firing and automatic weapons, radar for target tracking, and radio-operated fuses. British and U.S. forces used a 40-mm gun that fired ammunition to a height of 2 mi (3.2 km). Heavier guns , up to 120 mm, were used against high-flying bombers. For most of the war, the most effective was the German 88-mm Fliegerabwehrkanone ; its abbreviated name, flak, became a universal term for antiaircraft fire. With the introduction of guided missiles in the 1950s and '60s, heavy antiaircraft guns were phased out, though lighter radar-guided automatic guns remained effective against low-flying aircraft and helicopters.