Warships and craft of every kind maintained by a nation for fighting on, under, or over the sea. A large modern navy includes aircraft carriers, cruisers, destroyers, frigates, submarines, minesweepers and minelayers, gunboats, and various types of support, supply, and repair ships, as well as naval bases and ports. Naval ships are the chief means by which a nation extends sea power. Their two chief functions are to achieve sea control and sea denial. Control of the sea enables a nation and its allies to carry on maritime commerce, amphibious assaults, and other seaborne operations that may be essential in wartime. Denial of the sea deprives enemy merchant vessels and warships of safe navigation. See alsoU.S. Navy.