a naval surface ship designed to protect large ships and transports en route to the open sea or anchored in roads from attacks by submarines, airplanes, and cutters and to patrol shore approaches. Escort vessels appeared during World War I and were used against submarines. They were used extensively in World War II and have been retained in most fleets. Foreign escort vessels have displacements of 1,200–4,000 tons and speeds up to 30 knots (55.5 km/hr). Their armament includes one or two 76–127-mm automatic artillery guns, up to six 20–40-mm antiaircraft automatic guns, torpedo tubes, antisubmarine guided missiles, depth charges, and hydroacoustic and radar equipment.