HMS Unicorn was an aircraft repair ship and light aircraft carrier built for the Royal Navy in the late 1930s. She was completed during World War II and provided air cover over the amphibious landing at Salerno, Italy, in September 1943. The ship 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 British Pacific Fleet (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 BPF's 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 light carrier of the Far East Fleet, as the Eastern Fleet had been redesignated after the end of 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.Hobbs 2007, pp. 58–59 The ship returned to the UK after the end of the war and was again placed in reserve. She was listed for disposal in 1958 and sold for scrap in 1959.

Design and description 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 tenders supported those types. Such a ship would be able to perform a wider range of aircraft repair and maintenance tasks than aircraft carriers and on the full range of aircraft operated by the Royal Navy, including amphibians. Admiral Reginald Henderson, Controller of the Navy was instrumental for gaining approval for the ship and ensuring that she had a complete flight deck that would allow her to land, service and launch aircraft on active operations.Friedman, p. 172 She 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".Hobbs 2007, p. 41 In practice, Unicorn proved the value of the concept and two similar support ships, and were converted into aircraft maintenance ships by modifying light aircraft carriers still under construction.Friedman, pp. 237, 239

Unicorn had an overall length of , a beam of , and a draught of at deep load. She was somewhat overweight as completed and displaced at standard load rather than her designed .Lenton, p. 106 Each of the ship's two sets of Parsons geared steam turbines drove one propeller.Brown 1984, p. 23 Steam was supplied by six Admiralty three-drum water-tube boilers operating at a pressure of . The turbines were designed for a total of and gave Unicorn a speed of . The ship carried of fuel oil which gave her a range of at .

In order to land aircraft aboard, Unicorn was designed with a full-length, -long flight deck with arresting gear. She was also fitted with a catapult capable of launching a aircraft to a speed of .Ford, p. 416 The ship had two hangars, each high. The upper hangar was 324ft by 65ft, and the lower 360ft by 62ft. Aircraft were transported between the hangars and the flight deck by two aircraft lifts (elevators); the forward lift measured and the rear one . Unicorn could carry about 36 operational aircraft. Bulk petrol storage consisted of .Friedman, p. 367 During wartime, the ship's crew totaled 1200.Chesneau, p. 21 The ship carried a self-propelled lighter under the rear of the flight deck to allow unflyable aircraft to be transferred between ships or to shore facilities. This lighter was lowered flush with the upper hangar deck so that an aircraft could be rolled onto it or an aircraft could be lifted onto it once the lighter was in the water.Hobbs, p. 43

Unicorn was armed with four twin mounts for the 45-calibre QF 4-inch Mk XVI dual purpose gun. This mounting could elevate from −10 to +80°. The Mk XVI gun fired about 12 high-explosive shells per minute at a muzzle velocity of . Against surface targets it had a range of and a maximum ceiling of , but an effective anti-aircraft range of much less.Campbell, p. 56 She was also equipped with four quadruple mounts for the QF 2-pounder Mk VIII gun ("pom-pom"). These gun mounts could depress to −10° and elevate to a maximum of +80°. The Mk VIII 2-pounder gun fired a shell at a muzzle velocity of to a distance of . The gun's rate of fire was approximately 96–98 rounds per minute.Campbell, pp. 71–74 Close-range air defence was provided by twelve Oerlikon autocannon, in two twin mounts and eight single ones. The Oerlikon fired a shell at a muzzle velocity of . It had a rate of fire of 465–480 rounds per minute and a maximum range of .Campbell, pp. 75–76

The ship was equipped with two HACS (High Angle Control System) directors on her island and each "pom-pom" mount had its own director as well. Unicorn was the first ship to mount a Type 281B early-warning radar,Howse, p. 169 and each HACS director was fitted with a Type 285 gunnery radar.

Construction and service Unicorn was ordered on 14 April 1939, and laid down at Harland and Wolff in Belfast, Northern Ireland on 29 June. Her construction was delayed several times in favour of higher priority projects and she was not launched until 20 November 1941. The ship was completed on 12 March 1943. In order to accelerate the ship's completion, the Admiralty decided in 1942 that she would not be equipped with her full suite of maintenance and repair equipment.Hobbs, p. 44 Excluding her armament, Unicorn cost £2,531,000.

Whilst working up, 818 and 824 Squadrons flew aboard in April 1943; 818 Squadron had nine Fairey Swordfish torpedo bombers and 824 Squadron had six. 887 Squadron, with nine Supermarine Seafire IIC fighters was also embarked.Sturtivant, pp. 238, 258, 370 In late May, Unicorn escorted Convoy MKF 15 to Gibraltar while carrying a number of Royal Air Force Bristol Beaufighters that she off-loaded there. She escorted the returning convoy back to the Clyde in early June. Together with the aircraft carrier , the ship made a sweep towards the Norwegian coast as part of Operation Governor, a diversion for the Allied landings in Sicily in early July.Hobbs 2007, p. 45 For this operation, 887 Squadron was replaced by 800 Squadron with Hawker Sea Hurricanes.Sturtivant, pp. 157–158, 370

Unicorn was assigned to Force V, a flotilla of British carriers, commanded by Admiral Philip Vian, intended to provide air cover to Operation Avalanche, the Allied landings at Salerno. In preparation for this mission, the ship disembarked all of her Swordfish, except for three from 818 Squadron for self-defence and the Sea Hurricanes of 800 Squadron. They were replaced by Seafires of 809 and 897 Squadrons. Each of the Seafire squadrons had 10 aircraft, for a total of 33.Brown, J. D., p. 65 Unicorn joined the escort carriers of Force V in August at Gibraltar before they moved forward to the Central Mediterranean for intensive training prior to the commencement of the amphibious landing on 9 September.Hobbs 2007, pp. 45–46

The ship's Seafires flew 75 sorties on the first day of operations and 60 on 10 September but the Seafire was not well suited to carrier landings in low wind conditions and many were damaged in landing accidents. 44 sorties were flown on 11 September and only 18 on 12 September, even though Unicorns mechanics had managed to repair ten Seafires over the previous night. The fighter shortage grew so acute during the operation that fighters from the carriers Illustrious and , intended to provide distant cover against an attempt by the Italian fleet to interfere with the invasion, staged forward to Unicorn in order to provide air cover over the landings.Hobbs 2007, pp. 46–47 By 12 September, the situation had improved so that 887 Squadron was able to fly off six Seafires to a temporary airfield ashore. The ship returned to the UK on 20 September with a full load of damaged Seafires, in addition to her own aircraft, that were off-loaded at Glasgow to be repaired. Afterwards, she was refitted by her builders and reconfigured for her designed role as an aircraft repair ship.Hobbs 2007, p. 47

In the Far East

At the end of December 1943, Unicorn joined Illustrious, the battlecruiser and the battleships and , the other reinforcements for the Eastern Fleet. Only four Swordfish from 818 Squadron were carried aboard at this time.Sturtivant, p. 238 The ship delivered a consignment of aircraft to Royal Navy Air Station Cochin, India, on 27 January 1944 before arriving at Trincomalee, Ceylon on 2 February. In addition to her repair duties, the ship was often used for deck-landing practice. She was given a brief refit in Bombay during May.Hobbs 2007, p. 48 On 23 August, 818 Squadron was transferred to and later disbanded. On 7 November, 817 Squadron flew aboard to provide anti-submarine protection with its Fairey Barracudas as Unicorn was ordered to Durban, South Africa.Sturtivant, pp. 236, 238 There she was to be modified with separate workshops and additional equipment to accommodate American engines which used different screw threads and electrical fittings.Hobbs 2007, pp. 48, 52

That same month, Unicorn was transferred to the new BPF. She left Durban on 1 January 1945 and arrived at Colombo, Ceylon where she conducted deck-landing practice for pilots new to the BPF. The ship loaded 82 aircraft and 120 engines later in the month for transport to Australia, emptying the stocks of the Eastern Fleet, and departed for Sydney on 29 January. Unicorn arrived on 12 February and disembarked her stored aircraft. She sailed for Manus Island, in the Admiralty Islands, on 28 February to support the BPF's training before the opening stages of Operation Iceberg. The ship arrived at San Pedro Bay, Philippines on 27 March which was to serve as the BPF's intermediate replenishment base while it supported Operation Iceberg.Hobbs 2007, pp. 52–53

The BPF was to attack Japanese airfields in the Sakishima Islands and Formosa before and during the early stages of the invasion of Okinawa. Unicorn was primarily engaged in preparing aircraft for issue to the operational squadrons aboard the fleet carriers, rather than repair them, but she did repair, modify or service 105 aircraft in March–May 1945.Hobbs 2011, p. 165 The ship sailed for Australia on 22 May and arrived in Sydney on 1 June. She sailed for Brisbane on 6 June to have her bottom cleaned at the Cairncross Dockyard and to load more replacement aircraft. Unicorn arrived at Manus on 22 July to prepare for operations off Japan. She was still there when Japan surrendered on 15 August. The ship began to ferry aircraft, equipment and men back to Australia after the surrender, a task which ended on 6 November, when she arrived at Sydney. Unicorn departed for home in December 1945 and arrived in Plymouth in January 1946. She was decommissioned and placed in reserve.Hobbs 2007, pp. 38, 54–55

Post-war