Aircraft carriers today

Aircraft carriers are generally the largest ships operated by navies; a Nimitz class carrier powered by two nuclear reactors and four steam turbines is 1092 feet (333 m) long and costs about $4.5 billion. The United States has the majority of aircraft carriers with eleven in service, one under construction, and one on order. Its aircraft carriers are a cornerstone of American power projection capability.

Nine countries maintain a total of 20 aircraft carriers in active service: United States, United Kingdom, France, Russia, Italy, India, Spain, Brazil, and Thailand. In addition the People's Republic of China's People's Liberation Army Navy possesses the former Soviet aircraft carrier Varyag, but most naval analysts believe that they have no intention to operate it, but instead are using Varyag to learn about carrier operations for future Chinese aircraft carriers. The United States, South Korea, United Kingdom, Canada, the People's Republic of China, India, Japan, Australia, Chile, Singapore and France also operate vessels capable of carrying and operating multiple helicopters.

Aircraft carriers are generally accompanied by a number of other ships, to provide protection for the relatively unwieldy carrier, to carry supplies, and to provide additional offensive capabilities. This is often termed a battle group or carrier group, sometimes a carrier battle group.

In the early 21st century, worldwide aircraft carriers are capable of carrying about 1250 aircraft. US carriers account for over 1000 of these. The United Kingdom and France are both undergoing a major expansion in carrier capability (with a common ship class), but the United States will still maintain a very large lead.

Flight deck

As "runways at sea," modern aircraft carriers have a flat-top deck design that serves as a flight deck for take-off and landing of aircraft. Aircraft take off to the front, into the wind, and land from the rear. Carriers steam at speed, for example up to 35 knots (65 km/h), into the wind during take-off in order to increase the apparent wind speed, thereby reducing the speed of the aircraft relative to the ship. On some ships, a steam-powered catapult is used to propel the aircraft forward assisting the power of its engines and allowing it to take off in a shorter distance than would otherwise be required, even with the headwind effect of the ship's course. On other carriers, aircraft do not require assistance for take off — the requirement for assistance relates to aircraft design and performance. Conversely, when landing on a carrier, conventional aircraft rely upon a tailhook that catches on arrestor wires stretched across the deck to bring them to a stop in a shorter distance than normal. Other aircraft — helicopters and V/STOL (Vertical/Short Take-Off and Landing) designs — utilize their hover capability to land vertically and so require no assistance in speed reduction upon landing.

Conventional ("tailhook") aircraft rely upon a landing signal officer (LSO) to control the plane's landing approach, visually gauging altitude, attitude, and speed, and transmitting that data to the pilot. Before the angled deck emerged in the 1950s, LSOs used colored paddles to signal corrections to the pilot. From the late 1950s onward, visual landing aids such as mirrors provided information on proper glide slope, but LSOs still transmit voice calls to landing pilots by radio.

Since the early 1950s it has been common to direct the landing recovery area off to port at an angle to the line of the ship. The primary function of the angled deck landing area is to allow aircraft who miss the arresting wires, referred to as a "bolter", to become airborne again without the risk of hitting aircraft parked on the forward parts of the deck. The angled deck also allows launching of aircraft at the same time as others land.

The above deck areas of the warship (the bridge, flight control tower, and so on) are concentrated to the starboard side of the deck in a relatively small area called an "island". The starboard side of the ship is used for the island because early carrier pilots showed a tendency to veer left in a crash situation. Very few carriers have been designed or built without an island and such a configuration has not been seen in a fleet sized carrier. The "flush deck" configuration proved to have very significant drawbacks, complicating navigation, air traffic control and numerous other factors.

A more recent configuration, used by the British Royal Navy, has a 'ski-jump' ramp at the forward end of the flight deck. This was developed to help launch VTOL (or STOVL) aircraft (aircraft that are able to take off and land with little or no forward movement) such as the Sea Harrier. Although the aircraft are capable of flying vertically off the deck, using the ramp is more fuel efficient. As catapults and arrestor cables are unnecessary, carriers with this arrangement reduce weight, complexity, and space needed for equipment. The disadvantage of the ski jump — and hence, the reason this configuration has not appeared on American supercarriers — is the penalty that it exacts on aircraft size, payload and fuel load (and hence, range): Large, slow planes such as the E-2 Hawkeye and heavily-laden strike fighters like the F/A-18E/F Super Hornet cannot use a ski jump because their high weight requires either a longer takeoff roll than is possible on a carrier deck, or catapult assistance.