When the First Lord of the Admiralty, Earl Stanhope, was asked to select a name for a new aircraft carrier he chose the name Unicorn, not realising that the name was already in use by a wooden frigate built in 1824. To avoid embarrassment, the Frigate's name was changed to Unicorn II in 1939, and in 1941 she became HMS Cressy when it was found that having two ships named Unicorn created great confusion with mail and drafting.
In 1959, after the aircraft carrier had been scrapped, the Frigate was renamed HMS Unicorn by Mrs Keay, widow of Captain WF Keay who had commanded Unicorn throughout the war.
Unicorn (Pennant number : I72 ) was the aircraft carrier equivalent of a submarine/destroyer depot ship, and the modern day RFA Argus. She was fitted out to operate and support any aircraft used by the Fleet Air Arm, with a full flight deck, catapults, arrester gear, a crane for seaplane/floatplane handling and a 16.5' hangar headroom. She followed the layout of conventional carriers - and was visibly influenced by the Invincible and Ark Royal class.
Internally, there were workshop facilities, and stores including 36,000 gallons of aviation fuel. Upper and lower hangars had large lifts to accommodate any Fleet Air Arm aircraft, and the repairs were done in the hangars. The AA armament was controlled by two AR type 285 RDF fitted HA/DCT's and three AR type 282 fitted barrage directors. AW type 290 was carried at the masthead. HMS Unicorn was initially operational in March till October 1943, with aircraft from the Fleet Air Arm units: 800 Sea hurricanes, 818 swordfish, 824 swordfish, 887 seafire, 897 spitfire, 885 seafire squadrons.
She saw service in the Atlantic, Norway and the Mediterranean.
HMS Unicorn was completed in 1943, in time to join the Escort carriers of Force V, tasked to provide the fighter cover for both fleet and forces ashore in the first 24 hours following the landings at Salerno. In the event, it was nearly four days before the capture of an airfield ashore could relieve the force of the responsibility, during which time the combination of the carrier's low speed and small decks while operating in near windless conditions, wrote off over 40 Supermarine Seafire fighters in deck accidents alone.
The Unicorn's 6-knot speed advantage and larger deck prevented even more losses. On 24 March 1943, aircraft from 800, 818 and 824 squadrons embarked in HMS Unicorn for deck landing training in the Clyde and A/S operations around UK waters, disembarking to Machrihanish on the 13 May 1943.
On 8 June, 1943 they re-embarked in HMS Unicorn, attached to the Home Fleet, and carried out a sweep to the north of Norway with HMS Illustrious, during which, the Martlets of the two carriers shot down two Bf 138's without further attacks from the enemy, and returning safely early in July 1943, her squadrons disembarking to Machrihanish.
In late August 1943, Unicorn was part of Force H, provided support and air cover along with the carriers HMS Illustrious and HMS Formidable in the Salerno Allied landings on mainland Italy. An American CVL and 4 escort carriers provided air cover. This contrasted with the Anzio landings that followed in early September which were done without carrier support and received heavy casualties. HMS Uganda, HMS Warspite and USS Savannah badly damaged by glider bombs, and the destroyer USS Rowan sunk by MTBs.
HMS Unicorn then reverted to supply and repair duties, for aircraft repair and transport, and fleet backup and support. By early 1944, Unicorn was in the Far East, still doubling as operational carrier pending the delayed arrival of the Victorious. During this time she maintained a squadron of Fairey Barracuda, from November 1944-January 1945 with 817 squadron. During December 1944, HMS Unicorn was busy in establishing the MONABs in Australia. An advance party of MONAB II was landed from Unicorn that month, arriving at RAAF Bankstown, Sydney, New South Wales, Australia. Unloaded from the carrier were 16 crated aircraft, 8 Corsair IIs & 8 Martinet TT.Is from the RN Aircraft Depot at Cochin, S. India, these were to be assembled by the advance party, with RAAF assistance. Gloster Meteors for 77 RAAF Squadron in Korea, on the flight deck of HMS Unicorn, Singapore 1951
Laid up for several years after the war, she was reactivated for the Korean War. Between June 1950 and October 1953, HMS Unicorn filled a vital support role to the Royal Navy and Commonwealth Aircraft carriers in Korean waters and on several occassions accompanied the operational carrier to the forward area, flying her own aircraft and acting as a spare deck. On one occasion she engaged enemy positions in North Korea with her own 4inch guns, thereby becoming more closely engaged than any of the other carriers.
Unicorn was sold for scrap in June 1959, and was stripped at Dalmuir and hull broken up at Troon from March 1960.