artillery piece that is fired from the ground or shipboard in defense against aerial attack. Antiaircraft weapons development began as early as 1910, when the airplane first became an effective weapon. In World War I, field artillery pieces up to about 90 mm (3.5 inches) in calibre were converted to antiaircraft use by mountings that enabled them to fire nearly vertically. Aiming methods were inadequate, however, and in the interwar decades great progress was made in the development of range finders, searchlights, time fuzes, and gunlaying mechanisms to help artillery pieces hit the rapidly moving targets presented by aircraft.