A warship or combatant ship is a naval ship that is used for naval warfare. Usually they belong to the navy branch of the armed forces of a nation, though they have also been operated by individuals, cooperatives and corporations. As well as being armed, warships are designed to withstand damage and are typically faster and more maneuverable than merchant ships. Unlike a merchant ship, which carries cargo, a warship typically carries only weapons, ammunition and supplies for its crew.
In wartime, the distinction between warships and merchant ships is often blurred. Until the 17th century it was common for merchant ships to be pressed into naval service, and not unusual for more than half of a fleet to be composed of merchant ships—there was not a large difference in construction, unlike the difference between a heavily armoured battleship and an ocean liner. Until the threat of piracy subsided in the 19th century, it was normal practice to arm larger merchant ships such as galleons. Warships have also often been used as troop carriers or supply ships, such as by the French Navy in the 18th century or the Imperial Japanese Navy during the Second World War. In war since the early 20th century, merchant ships were often armed and used as auxiliary warships, such as the Q-ships of the First World War and the armed merchant cruisers of the Second World War.
The main types of warships today are, in order of decreasing size: aircraft carriers – amphibious assault ships – cruisers – destroyers – frigates – corvettes – fast attack boats. A more extensive list follows:
Submarine, are ships capable of staying submerged for days. Modern submarines can stay underwater for months, with food supplies as the only limiting factor.
Fleet submarine is a type of submarine with the speed, range, and endurance to operate as part of a navy's battle fleet.
Ballistic missile submarine is a submarine capable of deploying submarine-launched ballistic missiles (SLBMs) with nuclear warheads.
Cruise missile submarine are submarines equipped with cruise missiles.
Attack submarine is a submarine with the purpose of attacking other submarines.
Coastal submarine or littoral submarine is a small, maneuverable type of submarine with shallow draft well suited to navigation of coastal channels and harbors.
Midget submarine is any submarine under 150 tons, typically operated by a crew of one or two but sometimes up to six or nine.
Submarine aircraft carrier is a submarine equipped with aircraft for observation or attack missions. These submarines saw their most extensive use during World War II, although their operational significance remained small.
Cruiser submarine were a type of a very large submarine designed to remain at sea for extended periods in areas distant from base facilities.
Amphibious warfare ships are warships employed to land and support ground forces, such as marines, on enemy territory during an amphibious assault.
Amphibious assault ship is a type of amphibious warfare ship employed to land and support ground forces with ship-deployed helicopters and V/STOL aircraft on enemy territory by an amphibious assault.
Landing helicopter dock is a multipurpose amphibious assault ship that is capable of operating as a helicopter carrier and also has a well deck for supporting landing crafts.
Amphibious transport dock is an amphibious warfare ship, that embarks, transports, and lands elements of a landing force for expeditionary warfare missions.
Dock landing ship is an amphibious warfare ship with a well dock to transport and launch landing craft and amphibious vehicles.
Landing craft are small and medium seagoing watercraft, such as boats and barges, used to convey a landing force (infantry and vehicles) from the sea to the shore during an amphibious assault.