HMS Unicorn (I72)

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.[3] 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".[4] In practice, Unicorn proved the value of the concept and two similar support ships, Perseus and Pioneer were converted into aircraft maintenance ships by modifying light aircraft carriers still under construction.[5]

Unicorn had an overall length of 640 feet (195.1 m), a beam of 90 feet 3 inches (27.5 m), and a draught of 23 feet (7.0 m) at deep load. She was somewhat overweight as completed and displaced 16,510 long tons (16,770 t) at standard load rather than her designed 14,750 long tons (14,990 t).[6] Each of the ship's two sets of Parsons geared steam turbines drove one 15-foot (4.6 m) propeller.[7] Steam was supplied by six Admiralty three-drum water-tube boilers operating at a pressure of 400 psi (2,758 kPa; 28 kgf/cm²). The turbines were designed for a total of 40,000 shaft horsepower (30,000 kW) and gave Unicorn a speed of 24 knots (44 km/h; 28 mph).[6] The ship carried 3,000 long tons (3,000 t) of fuel oil which gave her a range of 7,000 nautical miles (13,000 km; 8,100 mi) at 13.5 knots (25.0 km/h; 15.5 mph).[7]

In order to land aircraft aboard, Unicorn was designed with a full-length, 600-foot (180 m)-long flight deck with arresting gear. She was also fitted with a catapult capable of launching a 14,000-pound (6,400 kg) aircraft to a speed of 66 knots (122 km/h; 76 mph).[8] The ship had two hangars, each 16 feet 6 inches (5.03 m) 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 33 by 45 feet (10.1 m × 13.7 m) and the rear one 24 by 46 feet (7.3 m × 14.0 m). Unicorn could carry about 36 operational aircraft. Bulk petrol storage consisted of 36,500 imperial gallons (166,000 l; 43,800 US gal).[9] During wartime, the ship's crew totaled 1200.[10] 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.[11]

Unicorn was armed with four twin mounts for the 45-calibre QF 4-inch Mk XVI dual purpose gun.[6] This mounting could elevate from −10 to +80°. The Mk XVI gun fired about 12 35-pound (16 kg) high-explosive shells per minute at a muzzle velocity of 2,660 ft/s (810 m/s). Against surface targets it had a range of 19,850 yards (18,150 m) and a maximum ceiling of 39,000 ft (12,000 m), but an effective anti-aircraft range of much less.[12] She was also equipped with four quadruple mounts for the 40-millimetre (1.6 in) QF 2-pounder Mk VIII gun ("pom-pom").[10] These gun mounts could depress to −10° and elevate to a maximum of +80°. The Mk VIII 2-pounder gun fired a 40-millimetre (1.6 in) 0.91-pound (0.41 kg) shell at a muzzle velocity of 1,920 ft/s (590 m/s) to a distance of 3,800 yards (3,500 m). The gun's rate of fire was approximately 96–98 rounds per minute.[13] Close-range air defence was provided by twelve 20 mm Oerlikon autocannon, in two twin mounts and eight single ones.[6] The Oerlikon fired a 0.272-pound (0.123 kg) shell at a muzzle velocity of 2,750 ft/s (840 m/s). It had a rate of fire of 465–480 rounds per minute and a maximum range of 4,800 yards (4,400 m).[14]

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.[6] Unicorn was the first ship to mount a Type 281B early-warning radar,[15] and each HACS director was fitted with a Type 285 gunnery radar.[6]

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.[6] 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.[16] Excluding her armament, Unicorn cost £2,531,000.[7] [Note 1]

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 during this time.[18] 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 Illustrious, 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.[19] For this operation, 887 Squadron was replaced by 800 Squadron with Hawker Sea Hurricanes.[20]

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 a small detachment of 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.[21] 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.[22]

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 Unicorn's 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 Formidable, 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.[23] By 12 September, the situation had improved so that 887 Squadron was able to fly off six Seafires to a temporary airfield ashore.[21]

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.[24]

In the Far East

Unicorn and Illustrious in Ceylon, 1944

At the end of December 1943, Unicorn joined Illustrious, the battlecruiser Renown and the battleships Queen Elizabeth and Valiant, the other reinforcements for the Eastern Fleet.[25] Only four Swordfish from 818 Squadron were carried aboard at this time.[26] 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.[25] On 23 August, 818 Squadron was transferred to Atheling and later disbanded. On 7 November, 817 Squadron flew aboard to provide anti-submarine protection with its Fairey Barracudas[27] as Unicorn was ordered to Durban, South Africa. There she was to be modified with separate workshops and additional equipment to accommodate American engines which used different screw threads and electrical fittings.[28]

That same month, Unicorn was transferred to the newly formed 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 available 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.[29]

The BPF was tasked 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 during this time,[30] rather than repair them, but she did repair, modify or service 105 aircraft in March–May 1945. 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.[31]

Post-war

HMS Unicorn with U.S. Navy ships at Sasebo, Japan, 1950

In 1949, Unicorn was reactivated for service in the Far East, in support of the carrier Triumph. She sailed from HMNB Devonport on 22 September with a cargo of Seafires and Fireflies. When the Korean War broke out in June 1950, the ship was disembarking aircraft, equipment and her maintenance personnel at RAF Sembawang, Singapore in preparation to return home and then to reserve. The Admiralty ordered her to be used as a replenishment carrier to ferry replacement aircraft and supplies to the Royal Navy and Commonwealth aircraft carriers operating in Korean waters. Unicorn left Singapore on 11 July and arrived at Sasebo, Japan, on 20 July and transferred seven Seafires and five Fireflies to Triumph. In August, the ship ferried the 1st Battalion of the Middlesex Regiment and the Headquarters of the 27th Brigade from Hong Kong to Pusan, arriving on 29 August. She delivered supplies to Sasebo before returning to Singapore to begin a refit.[32]

Unicorn resumed her duties in December, carrying about 400 troops in addition to the usual aircraft, stores and equipment. She was used by pilots for deck-landing practice en route. In March, she ferried the Gloster Meteor jet fighters of No. 77 Squadron RAAF to Iwakuni, Japan. The ship remained there for the next three months so she could be used as an accommodation ship. Afterwards, Unicorn resumed her role as a ferry carrier. Whilst transiting the Shimonoseki Strait on 2 October, she destroyed the overhead power cables stretching between Honshu and Kyushu as they were sagging lower than normal due to a heavy snowfall. On 21 November, Unicorn and the carrier Warrior exchanged crews at Singapore and the ship began a refit shortly afterwards. After her refit was completed on 20 January 1952, she returned to her ferry duties.[33] In April, she was "adopted" by the Middlesex Regiment (possibly one of only three ships to be honoured by an Army regiment).[34] During operations by Ocean in July, the ship acted as a spare flight deck to allow for damaged aircraft to land without disrupting the strike operations. She arrived back at Singapore on 27 July to load more replacement aircraft, including Meteors, and sailed on 9 August for Japan. During September, Unicorn borrowed four of Ocean's Hawker Sea Fury fighters to fly combat air patrols over the fleet whilst the latter ship conducted strike operations. She was docked for maintenance in October, and embarked the First Sea Lord, Admiral Rhoderick McGrigor and the Commander-in-Chief, Far East Station for a tour of Commonwealth forces in Japan. At one point, Unicorn became the only aircraft carrier to conduct a shore bombardment during wartime when she engaged North Korean coastwatchers at Chopekki Point.[35]

The ship returned to Singapore for another refit on 15 December and did not leave Singapore until 17 July 1953. On 26 July, en route for Japan, Unicorn received a distress call from SS Inchkilda, saying that she was under attack by pirates. The carrier closed on the freighter's position at high speed and the pirates abandoned their prize when Unicorn circled the freighter with all guns bearing at less than 3,000 yards (2,700 m). The Korean Armistice Agreement came into effect the following day, but the ship accompanied Ocean on two patrols on 30 July and 25–29 August to monitor North Korean compliance with the terms of the armistice. She sailed for home on 15 October and arrived at Devonport on 17 November, where she returned to reserve.[36]

• Aircraft maintenance carriers of the Royal Navy

• Brown, D. K. (1984). "HMS Unicorn: The Development of a Design 1937–39". In Gray, Randal (ed.). Warship VIII. London: Conway Maritime Press. pp. 19–24. ISBN 0-85177-354-0.
• Blackman, Raymond V. B. (ed.). Jane's Fighting Ships 1953–54. New York: McGraw-Hill Book Company.
• Brown, J. D. (2009). Carrier Operations in World War II. Annapolis, Maryland: Naval Institute Press. ISBN 978-1-59114-108-2.
• Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich: Conway Maritime Press. ISBN 0-85177-146-7.
• Campbell, John (1985). Naval Weapons of World War II. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-459-4.
• Colledge, J. J.; Warlow, Ben (2006) [1969]. Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8.
• Ford, Roger; Gibbons, Tony; Hewson, Rob; Jackson, Bob; Ross, David (2001). The Encyclopedia of Ships. London: Amber Books. ISBN 978-1-905704-43-9.
• Friedman, Norman (1988). British Carrier Aviation: The Evolution of the Ships and Their Aircraft. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-054-8.
• Hobbs, David, Commander (2007). Moving Bases: Royal Navy Maintenance Carriers and MONABs. Liskeard, Cornwall, UK: Maritime Books. ISBN 978-1-904459-30-9.
• Hobbs, David, Commander (2011). The British Pacific Fleet: The Royal Navy's Most Powerful Strike Force. Annapolis, Maryland: Naval Institute Press. ISBN 978-1-59114-044-3.
• Howse, Derek (1993). Radar at Sea: The Royal Navy in World War 2. Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-704-X.
• Lenton, H. T. (1998). British & Commonwealth Warships of the Second World War. Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-048-7.
• McCluskie, Tom (2013). The Rise and Fall of Harland and Wolff. Stroud: The History Press. ISBN 978-0-7524-8861-5.
• Sturtivant, Ray (1984). The Squadrons of the Fleet Air Arm. Tonbridge, UK: Air-Britain (Historians). ISBN 0-85130-120-7.

Wikimedia Commons has media related to HMS Unicorn (I72).

• Obituary of Captain George Baldwin, former naval aviator on Unicorn
• Fleet Air Arm history of Unicorn
• The MONAB story at Archive.today (archived 2012-07-20)
• MaritimeQuest HMS Unicorn I-72 Pages
• HMS Unicorn during the Korean War