A helicopter carrier is a type of aircraft carrier whose primary purpose is to operate helicopters, and has a large flight deck that occupies a substantial part of the deck, which can extend the full length of the ship like HMS Oceanof 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 of 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-35, 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 amphibious assault ships.
Helicopter carriers have been used as anti-submarine warfare carriers and amphibious assault ships.
HMS Hermes and two of her sisters were 22,000 ton fleet carriers converted to "commando carriers" only able to operate helicopters. Hermes was later converted to a STOVL carrier.
[Wikipedia]
