HMS Ark Royal (91)

HMS Ark Royal (pennant number 91) was an aircraft carrier of the Royal Navy that was operated during the Second World War.

Designed in 1934 to fit the restrictions of the Washington Naval Treaty, Ark Royal was built by Cammell Laird at Birkenhead, England, and completed in November 1938. Her design differed from previous aircraft carriers. Ark Royal was the first ship on which the hangars and flight deck were an integral part of the hull, instead of an add-on or part of the superstructure. Designed to carry a large number of aircraft, she had two hangar deck levels. She was used during a period that first saw the extensive use of naval air power; several carrier tactics were developed and refined aboard Ark Royal.

Ark Royal operated in some of the most active naval theatres of the Second World War. She was involved in the first aerial U-boat kills of the war, operations off Norway, the search for the German battleship Bismarck, and the Malta Convoys. Ark Royal survived several near misses and gained a reputation as a 'lucky ship'. She was torpedoed on 13 November 1941 by the German submarine U-81 and sank the following day. One of her 1,488 crew members was killed. Her sinking was the subject of several inquiries, with investigators keen to know how the carrier was lost in spite of efforts to save the ship and tow her to the naval base at Gibraltar. They found that several design flaws contributed to the loss, which were rectified in new British carriers.

The wreck was discovered in December 2002 by an American underwater survey company using sonar mounted on an autonomous underwater vehicle, under contract from the BBC for the filming of a documentary about the ship, at a depth of about 3,300 feet (1,000 m) and approximately 30 nautical miles (56 km; 35 mi) from Gibraltar.

In 1923, the Admiralty prepared a 10-year building programme which included an aircraft carrier and 300 aircraft for the Fleet Air Arm. The economic downturn following the First World War caused it to be postponed. In 1930, the Director of Naval Construction, Sir Arthur Johns, began to update the plans for the carrier by incorporating recently developed technology. His aim was to increase the number of aircraft carried by shortening the landing and take-off distances of aircraft using arrestor gear and compressed steam catapults respectively, which would make more deck space available for storage and aircraft preparation. Along with the inclusion of two hangar decks, this allowed Ark Royal to carry up to 72 aircraft, although the development of larger and heavier aircraft during the carrier's construction meant that the actual number carried was between 50 and 60. Ark Royal featured an enclosed hangar design where the flight deck was the 'strength deck' and was strongly built with .75in (19mm) thick Ducol steel plating. The two hangar decks were thus enclosed within the hull girder, which also gave splinter protection to the hangars. The machinery spaces were protected by 4.5-inch (11.4 cm) belt armour. Three lifts moved aircraft between the hangars and the flight deck.

Another feature was the length and height of the flight deck. At 800 feet (240 m), the flight deck was 118 feet (36 m) longer than the keel; the latter dictated by the length of Royal Navy drydocks in Gibraltar and Malta. Due to the twin hangar decks, the flight deck rose to 66 feet (20 m) above the waterline.

The Washington and London Naval treaties had restricted warship displacement for a number of nations after the end of the Great War and were both to expire by the end of 1936. With a potential naval arms race developing between Britain, Japan and Italy, the British government sought a second treaty, which included limiting the maximum displacement of an aircraft carrier to 23,000 long tons (23,000 t). Ark Royal would have to fit this anticipated limit; to conserve weight, armour plating was limited to the belt, engine rooms, and magazines, while welding instead of rivetting 65% of the hull saved 500 long tons (510 t). Installation of an armoured flight deck was not possible, as the weight would have placed Ark Royal above the proposed limit, while reducing her endurance and stability. The ship was designed with a three-layer side protection system based upon a void-liquid-void scheme very similar to that used on the King George V-class battleships, and was designed to protect against torpedoes with up to a 750-pound (340 kg) warhead.

The ship was fitted with six boilers, which powered three Parsons geared turbines. The turbines were connected via three driveshafts to three propellers 16 feet (4.9 m) in diameter, to produce a maximum theoretical speed of 30 knots (56 km/h; 35 mph). Speed was important, as with catapults and arrestor gear, Ark Royal would have to turn into the wind to launch and recover aircraft. To avoid endangering other ships with the frequent course changes associated with flight operations, Ark Royal would have to break away from accompanying ships, and catch up on completion. Additionally, as the carrier was not armed for ship-to-ship combat, speed was her main protection against enemy warships.