An aircraft carrier is a warship that serves as a seagoing airbase, equipped with a full-length flight deck and facilities for carrying, arming, deploying, and recovering aircraft. Typically, it is the capital ship of a fleet, as it allows a naval force to project air power worldwide without depending on local bases for staging aircraft operations. Aircraft carriers are expensive to build and are critical assets. Aircraft carriers have evolved from converted cruisers to nuclear-powered warships that carry numerous fighter planes, strike aircraft, helicopters, and other types of aircraft.