List of aircraft maintenance carriers of the Royal Navy The Royal Navy built three aircraft maintenance carriers for its Fleet Air Arm before and during World War II . The Abyssinia Crisis of 1934 – 35 demonstrated to the Admiralty that it needed a depot ship to support the aircraft carriers in active service , just like submarine and destroyer tender s supported those types . Begun just before the start of World War II in 1939 , was the first ship built in any navy that could " carry out the full range of aircraft maintenance and repair work in addition to the ability to operate aircraft from the flight deck " . " Unicorn " proved the value of the concept and two similar support ships , and were converted into aircraft maintenance ships by modifying light carrier s while still under construction . Unlike " Unicorn " , neither " Pioneer " nor " Perseus " were able to land aircraft ; they had to be craned aboard . " Unicorn " was used as a light carrier in 1943 before she was sent to the Indian Ocean in 1944 where she was used in her designed role . " Pioneer " arrived the following year to support the British Pacific Fleet ( BPF ) . " Perseus " arrived in the Pacific after the end of the war . All three ships were placed in reserve upon their return to the UK in 1946 . " Unicorn " was recommissioned before the start of the Korean War for use as a ferry carrier , but was used in her designed role during the war . " Pioneer " was recommissioned in 1950 to test new carrier equipment and then became a ferry carrier . " Perseus " was never recommissioned and all three ships were sold for scrap during the 1950s . HMS " Unicorn " . HMS " Unicorn " was an aircraft repair ship built for the Royal Navy in the late 1930s . The ship was initially completed as a light aircraft carrier and provided air cover over the amphibious landing at Salerno , Italy in September 1943 . The ship converted back into a maintenance ship afterwards and she was transferred to the Eastern Fleet in the Indian Ocean at the end of the year . " Unicorn " supported the aircraft carriers of the fleet on their operations until the BPF was formed in November 1944 . She was transferred to Australia in early 1945 to support the BPF ' s operations during Operation Iceberg , the Allied invasion of Okinawa in May . To shorten the time required to replenish the British carriers , the ship was based in the Admiralty Islands and in the Philippine Islands until the Japanese surrender in August . " Unicorn " was decommissioned and placed in reserve when she returned to the UK in January 1946 . The ship was recommissioned in 1949 to support the carriers of the Far East Fleet , as the Eastern Fleet had been redesignated after World War II . She was unloading aircraft and equipment in Singapore in June 1950 when the Korean War began . She spent most of the war ferrying aircraft , troops , stores and equipment in support of Commonwealth operations in Korea . " Unicorn " supported other carriers during operations in Korea , but she became the only aircraft carrier to conduct a shore bombardment with her guns during wartime when she attacked North Korean observers on the coast during the war . The ship returned to the UK after the end of the war and was again placed in reserve . She was sold for scrap in 1959 . " Colossus " class . HMS " Pioneer " and HMS " Perseus " were not completed to their original design as " Colossus " - class light aircraft carriers ; the success of " Unicorn " prompted modification of the ships whilst under construction into aircraft maintenance ships without aircraft catapult s and deckhouses built on the flight deck . " Pioneer " arrived in Australia in early 1945 to support operations by the BPF against Japanese forces from a base in the Admiralty Islands . The ship and her facilities were used to help repair Hong Kong ' s infrastructure in late 1945 and she returned to the UK in early 1946 . " Pioneer " was immediately placed in reserve upon her arrival and she was sold in 1954 for scrap . " Perseus " was completed in 1945 , after the end of World War II , and she made a trip to Australia late in the year , just in time to help return men , aircraft and equipment . Upon her return to the UK in early 1946 , " Perseus " was placed in reserve . The ship was recommissioned in 1950 to serve as the trials ship for the steam catapult then under development . Over 1600 test launches were conducted before the catapult was removed in 1952 and she was converted for use as a ferry carrier to transport aircraft , troops and equipment overseas . She was reduced to reserve again in 1954 and sold for scrap in 1958 .