An aircraft carrier is a warship

Warship

A warship is a ship that is built and primarily intended for combat. Warships are usually built in a completely different way from merchant ships. As well as being armed, warships are designed to withstand damage and are usually faster and more maneuvrable than merchant ships...

 designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase

Airbase

An airbase is a military airfield that provides basing and support of military aircraft....

. Aircraft carriers thus allow a naval force

Navy

A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 to project air power worldwide without having to depend on local bases for staging aircraft operations. They have evolved from wooden vessels used to deploy balloon

Balloon

A balloon is an inflatable flexible bag filled with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. Modern balloons can be made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were made of dried animal bladders, such as the pig...

s into nuclear-powered

Nuclear propulsion

Nuclear propulsion includes a wide variety of propulsion methods that fulfil the promise of the Atomic Age by using some form of nuclear reaction as their primary power source.- Surface ships and submarines :...

 warships that carry dozens of fixed wing and rotary-wing

Rotorcraft

A rotorcraft or rotary wing aircraft is a heavier-than-air flying machine that uses lift generated by wings, called rotor blades, that revolve around a mast. Several rotor blades mounted to a single mast are referred to as a rotor. The International Civil Aviation Organization defines a rotorcraft...

 aircraft.

Aircraft carriers are typically treated as the capital ship

Capital ship

The capital ships of a navy are its most important warships; they generally possess the heaviest firepower and armor and are traditionally much larger than other naval vessels...

 of a fleet and are extremely expensive to build and important to protect: of the nine nations which possess an aircraft carrier, seven of these navies only possess one such ship.