USS Callaghan, guided missile destroyer of the Kidd class—Official U.S. Navy photograph
Fast naval vessel used to protect other ships. The term was first applied to vessels built in the 1890s to protect battleships from torpedo boats. By World War I destroyers were often sent ahead of the battle fleet to scout for the enemy, beat back its destroyers with cannon fire, and then launch torpedoes against its battleships and cruisers. When the submarine became the main torpedo-launching vessel, destroyers armed with depth charges protected convoys and battle fleets against submarine attack. In World War II, with the addition of radar and antiaircraft guns, its escort role included air defense. Modern destroyers are run by a crew of about 300 and equipped with surface-to-air missiles, antiship missiles, and one or two big guns. Many carry submarine-hunting helicopters, and some carry cruise missiles.