Aircraft carrier

An aircraft carrier is a warship whose main role is to deploy andrecover aircraft . Aircraft carriers thus allow a naval force to project air power great distances without having to depend on local bases for land-basedaircraft. Modern navies, who operate such ships, treat aircraft carriers as the centerpiece of the fleet, a role previouslyplayed by the battleship . The change, part of the growth of air power as asignificant part of warfare, took place during World War II . Unescortedcarriers are considered vulnerable to missile attack and therefore travel as part ofa carrier battle group .

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 ft (333 m) long and costs about $5 billion. The United States has the majority ofaircraft carriers with over a dozen in service, and its aircraft carriers are a cornerstone of American military power.

Nine countries maintain aircraft carriers: United States , France , India , Russia , Spain , Brazil , Italy , Thailand , and the United Kingdom . 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 a future Chinese aircraft carrier .

Aircraft carriers have two basic configurations. The most common has a flat top deck that serves as a take-off and landingarea for aircraft. A steam-powered catapult , invented by the Royal Navy , accelerates an aircraft under full throttle, from 0 to 165 mph (265 km/h)in 2 seconds during take-off to help it reach take-off speed. To land on the carrier, incoming aircraft moving at 150 mph (240km/h) are equipped with tailhooks to engage one of up to four arresting cables stretched across the deck, stopping the aircraftwithin 320 feet (100 m) after engaging a cable.

The second configuration, developed for the Royal Navy, has a 'ski-jump' at one end of the flat deck, that helps launch theaircraft. This arrangement is designed for use with VTOL or STOVL aircraft that are able to take off and land with little or no forward movement. These aircraft do not requirecatapult facilities or arrestor cables to be deployed across the flightdeck.

In either case the ship steams at up to 35 knots (64 km/h)straight into the wind during take-off and landing operations in order to increase the apparent wind speed, thereby reducing therequired speed of the aircraft relative to the ship.

There are six basic types of aircraft carriers:

• Seaplane tenders , out of use after World War II
• Assault carriers , such as USS Tarawa , which often also serve the purpose of carryingand landing troops
• ASW carriers , such as HMS Invincible , also known as a "helicopter carrier"
• Escort carriers , such as USS Barnes , only used during World War II
• Fleet carriers , such as the Admiral Kuznetsov ,typically 20,000 to 65,000 tons
• Supercarriers , such as USS Nimitz , typically 75,000 tons or more

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

Cruisers and other ships of the early twentieth century often carried a few catapult launched seaplanes that could berecovered by crane after landing on the water. These planes were often used for reconnaissance. Many modern warships have helicopter landing capability and helicopter assault ships represent a new formof aircraft carriers.