HMS Unicorn: The forerunner of the Light Fleet Aircraft Carrier?

In a recent comment to Part 2 of my recent blog posts about the 1942 Light Fleet Aircraft Carriers, Martin Rapier mentioned the apparent 'luxury' enjoyed by the Royal Navy of being able to have a maintenance carrier. In reply, I mentioned that the Royal Navy had actually designed and built a maintenance carrier before the 1942 Light Fleet Aircraft Carriers were designed, and that this ship was HMS Unicorn.

As a result of the Abyssinian Crisis in 1935, the Royal Navy realised that it needed to have some sort of depot ship for the aircraft carried aboard its ships in the same way that they had depot ships for destroyers, submarines, and smaller craft. HMS Unicorn was designed to meet this requirement, and because she was classified as a depot ship, she did not count towards the UK's aircraft carrier tonnage limit set by the London Naval Treaty.

From a distance, the design resembled a shorter version of the Illustrious-class armoured aircraft carriers, but she was armed more like the destroyer and submarine depot ships (e.g. HMS Woolwich and HMS Forth).

The ship's characteristics were as follows:

• Displacement:20,300 tons (deep load)
• Dimensions:
• Length: 640ft (195.1m)
• Beam: 90ft 3in (27.51m)
• Draught: 23ft (7.0m)
• Propulsion:4 x Admiralty 3-drum boilers providing steam to 2 x geared steam turbine (40,000shp), each driving a propeller
• Speed: 24 knots
• Range: 7,000 nautical miles at 13.5 knots
• Complement: 1,200 (wartime)
• Radar: 1 x Type 281B Early-warning radar; 2 x Type 285 gunnery radars
• Armament: 4 × twin 4-inch (102 mm) dual purpose guns; 4 × quadruple Mk. VIII 2-pounder (40 mm (1.6-inch)) anti-aircraft guns; 2 × twin and 8 × single 20mm (0.8-inch) Oerlikon anti-aircraft guns
• Armour:
• Flight deck: 2-inch (51mm)
• Magazines: 2 to 3-inch (51 to 76mm)
• Bulkheads: 1.5-inch (38mm)
• Aircraft carried: Approximately 33 (when used operationally)

HMS Unicorn was ordered on 14th April 1939, laid down at Harland & Wolf, Belfast on 26th June 1939, launched on 20th November 1941, and completed on 12th June 1943. Her completion was delayed in order that work on more urgently needed ships could be prioritised.

Due to the pressing need to get as many aircraft carriers as possible into service, HMS Unicorn was not fitted out for her original role. She escorted a number of convoys between Gibraltar and the Clyde before being attached to the flotilla providing air cover for the Allied landings at Salerno.

On her return to the UK in September of that year, she was refitted for her original role. In December 1943 HMS Unicorn was sent to the Far East to reinforce the Eastern Fleet. She remained there until the end of the war. HMS Unicorn returned to the UK in January 1946 and was decommissioned soon afterwards.

HMS Unicorn was recommissioned in 1949 to support Royal Naval operations in the Far East. As a result, she was available to support UN operation in Korea and actually conducted a bombardment of North Korean positions using her 4-inch guns.

In 1952 consideration was given to rebuilding her so that she could operate the newer, heavier aircraft that were coming into service. This would have required her being fitted with a steam catapult, the reinforcement and strengthening of her flight deck, moving and enlarging her forward aircraft lift, and fitting a newer aircraft-handling crane capable of lifting heavier aircraft. The refit was planned to take place in mid 1954, but it was cancelled so that the limited funds available could be used to refit other aircraft carriers with angled flight decks. Instead, HMS Unicorn was reclassified as a ferry carrier and placed in reserve in March 1957. She was sold for scrapping in June 1959.

Although the 1942 Light Fleet Aircraft Carriers were of a similar size and function to HMS Unicorn, there is no evidence that the design of the former was based in any way on that of the latter. HMS Unicorn was built by Harland & Wolf whereas the detailed design of the 1942 Light Fleet Aircraft Carriers was carried out by Vickers-Armstrong.