An airborne aircraft carrier is a type of mother ship aircraft which can carry, launch, retrieve and support other smaller parasite aircraft. The only dedicated examples to have been built were airships, although existing heavier-than-air aircraft have been modified for use in similar roles, and airborne aircraft carriers of various types appear in fiction, such as Cloudbase in Gerry Anderson's Captain Scarlet and the Mysterons, the Helicarrier from Marvel Comics, the Valiant from series 3 of Doctor Who, and an unnamed one in Sky Captain and the World of Tomorrow. Airship projects In July 1917, experiments were made with aircraft slung under HM Airship No. 23, in hopes that they could defend the airship. First an unmanned, then a manned, Sopwith Camel fighters were launched successfully. The experiment was successfully completed with two other manned Camels. The British Imperial Airship Scheme of 1924 initially envisaged an airship that could carry five fighter aircraft in military use, but this requirement was abandoned and the project saw only the civilian R100 and R101 airships to completion. Akron-class The two rigid airships of the , and , were built for scouting duties for the U.S. Navy and operational between 1931 and 1935. Following experiments with launching and recovering small aeroplanes using , the U.S. Navy designed Akron and Macon with internal hangars able to house a number of Curtiss F9C Sparrowhawk biplane fighters. The fighters were launched and recovered using a "trapeze" mechanism. With lengths of , Akron and Macon were among the largest flying objects in the world and still hold the world record for helium-filled airships. They were just shorter than the German hydrogen-filled airship Hindenburg. Akron first flew on 8 August 1931 and Macon followed on 21 April 1933. The Sparrowhawk fighters became operational in September 1932. Akron was destroyed on 4 April 1933 and Macon on 12 February 1935. During her accident-prone 18-month term of service, the Akron served as an airborne aircraft carrier for launching and recovering F9C Sparrowhawk fighter planes. Akron was destroyed in a thunderstorm off the coast of New Jersey on the morning of 4 April 1933, killing 73 of her 76 crewmen and passengers. This accident was the largest loss of life for any airship crash. Macon was designed to carry biplane parasite aircraft, five single-seat Curtiss F9C Sparrowhawks for scouting or two-seat Fleet N2Y-1 for training. In service for less than two years,