Frigate, a naval vessel designed to defend aircraft carriers and merchant ships against submarines. Frigates are usually smaller than destroyers. U.S. Navy frigates displace about 3,000 tons. They are armed with antiaircraft missiles, guns, and automatic cannon; antisubmarine missiles; and torpedoes. Frigates also carry sonar equipment for tracking submarines. (In the 1960's, the U.S. Navy had a number of large destroyers called frigates, but these vessels were later redesignated either cruisers or destroyers, depending on size.) British frigates generally displace less than 3,000 tons.

Originally, a frigate was a long, narrow merchant ship propelled by sails or oars. Frigates were common in the Mediterranean during the 16th and 17th centuries. During the late 1600's, a two-decked frigate was adapted for naval use by the British. British frigates of the late 1700's were three-masted ships ranging from 500 to 1,200 tons. They usually mounted from 30 to 50 guns.

U.S. Navy frigates built during the 1790's were somewhat larger than British frigates. During that period, these ships were used chiefly for scouting and convoy duty. The frigate USS Constellation saw action in the undeclared naval war against France, 1799–1800, and the USS Constitution (Old Ironsides) won fame in the War of 1812.

Steam frigates began to displace sailing frigates about 1855, and were in turn displaced by ironclad ships during the Civil War. During World War II, the British navy revived the name frigate for escort vessels that were somewhat smaller than destroyers.

The U.S. Navy developed a similar vessel but called it a destroyer escort. The Navy gradually increased the offensive capabilities of the vessel by adding guided missiles to its armament. The vessel no longer simply had escort functions, but could search out submarines. In 1975, the name of the destroyer escort class was changed to frigate to agree with international usage.