HMS Ocean (L12) in the context of "Supercarrier"

An aircraft carrier is a warship that serves as a seagoing airbase, equipped with a full-length flight deck and hangar facilities for supporting, arming, deploying and recovering shipborne aircraft. Typically it is the capital ship of a fleet (known as a carrier battle group), as it allows a naval force to project seaborne air power far from homeland without depending on local airfields for staging aircraft operations. Since their inception in the early 20th century, aircraft carriers have evolved from wooden vessels used to deploy individual tethered reconnaissance balloons, to nuclear-powered supercarriers that carry dozens of fighters, strike aircraft, military helicopters, AEW&Cs and other types of aircraft such as UCAVs. While heavier fixed-wing aircraft such as airlifters, gunships and bombers have been launched from aircraft carriers, these aircraft do not often land on a carrier due to flight deck limitations.

The aircraft carrier, along with its onboard aircraft and defensive ancillary weapons, is the largest weapon system ever created. By their tactical prowess, mobility, autonomy and the variety of operational means, aircraft carriers are often the centerpiece of modern naval warfare, and have significant diplomatic influence in deterrence, command of the sea and air supremacy. Since the Second World War, the aircraft carrier has replaced the battleship in the role of flagship of a fleet, and largely transformed naval battles from gunfire to beyond-visual-range air strikes. In addition to tactical aptitudes, it has great strategic advantages in that, by sailing in international waters, it does not need to interfere with any territorial sovereignty and thus does not risk diplomatic complications or conflict escalation due to trespassing, and obviates the need for land use authorizations from third-party countries, reduces the times and transit logistics of aircraft and therefore significantly increases the time of availability on the combat zone.

A naval fleet is the largest operational formation of warships in a navy, typically under a single command and organized for strategic missions. While modern fleets are permanent, multi-role forces (e.g., carrier strike groups), historical fleets were often ad hoc assemblies for specific campaigns. The term "fleet" can also synonymously refer to a nation’s entire navy, particularly in smaller maritime forces.

Fleets have shaped geopolitics since antiquity—from the trireme fleets of Athens to the nuclear-powered carrier groups of today—enabling power projection, trade protection, and deterrence. Multinational fleets, such as NATO’s Standing Maritime Groups, demonstrate their continued diplomatic-military role.

Following the September 11 attacks in 2001, several countries began military operations against Al-Qaeda and the Taliban during Operation Enduring Freedom (OEF) in Afghanistan. After the initial bombing operations, Operation Crescent Wind, OEF was the initial combat operations, and during 2002 and 2003.

This list covers United States and other states' forces and other forms of support for OEF from October 2001. Some nations' operations in Afghanistan continued as part of NATO's International Security Assistance Force (ISAF). For example, United States troops were deployed both in the OEF and ISAF.

A helicopter carrier is a type of aircraft carrier whose primary purpose is to operate helicopters. It has a large flight deck that occupies a substantial part of the deck, which can extend the full length of the ship like HMS Ocean of the Royal Navy (RN), or extend only partway, usually aft, as in the Soviet Navy's Moskva class or in the Chinese Navy's Type 0891A. It often also has a hangar deck for the storage and maintenance of rotorwing aircraft.

Pure helicopter carriers are difficult to define in the 21st century. The advent of STOVL aircraft such as the Harrier jump jet, and now the F-35B, have complicated the classification; the United States Navy's Wasp class, for instance, carries six to eight Harriers as well as over 20 helicopters. Only smaller carriers unable to operate the Harrier, and older, pre-Harrier-era carriers, can be regarded as true helicopter carriers. In many cases, other carriers, able to operate STOVL aircraft, are classified as "light aircraft carriers". Other vessels, such as the Wasp class, are also capable of embarking troops such as marines and landing them ashore; they are classified as landing helicopter docks.

Naval tactics and doctrine is the collective name for methods of engaging and defeating an enemy ship or fleet in battle at sea during naval warfare, the naval equivalent of military tactics on land.

Naval tactics are distinct from naval strategy. Naval tactics are concerned with the movements a commander makes in battle, typically in the presence of the enemy. Naval strategy concerns the overall strategy for achieving victory and the large movements by which a commandant or commander secures the advantage of fighting at a place convenient to himself.