Battle between the frigates HMS Shannon and USS Chesapeake off Boston during the War —The National Maritime Museum, London
Either of two different types of warships, of the 17th–19th centuries and of World War II and after. The sailing ship known as a frigate was a three-masted, fully rigged vessel, often carrying 30–40 guns in all. Smaller and faster than ships of the line, frigates served as scouts or as escorts protecting merchant convoys; they also cruised the seas as merchant raiders themselves. With the transition to steam, the term gradually gave way to cruiser. In World War II, Britain revived the term frigate to describe escort ships equipped with sonar and depth charges and used to guard convoys from submarines. In the postwar decades frigates also adopted an antiaircraft role, adding radar and surface-to-air missiles. Modern frigates may displace more than 3,000 tons (2,700 metric tons), sail at a speed of 30 knots, and carry a crew of 200.