HMS Illustrious was the lead ship of her class of aircraft carriers built for the Royal Navy before World War II. Her first assignment after completion and working up was with the Mediterranean Fleet, in which her aircraft's most notable achievement was sinking one Italian battleship and badly damaging two others during the Battle of Taranto in late 1940. In January 1941, during Operation Excess, Illustrious was hit multiple times by German and Italian dive bombers and was repaired in the United States. After sustaining damage on the voyage home in late 1941 by a collision with her sister ship , Illustrious was sent to the Indian Ocean in early 1942 to support the invasion of Vichy French Madagascar (Operation Ironclad).
After returning home in early 1943, the ship was given a lengthy refit and briefly assigned to the Home Fleet. She was transferred to Force H for the Battle of Salerno in mid-1943 and then rejoined the Eastern Fleet in the Indian Ocean at the beginning of 1944. Her aircraft attacked several targets in the Japanese-occupied Dutch East Indies over the following year before Illustrious was transferred to the newly formed British Pacific Fleet (BPF). The carrier participated in the early stages of the Battle of Okinawa until mechanical defects arising from accumulated battle damage became so severe she was ordered home early for repairs in May 1945.
The war ended while she was in the dockyard and the Admiralty decided to modify her for use as the Home Fleet's trials and training carrier. In this role she conducted the deck-landing trials for most of the British post-war naval aircraft in the early 1950s. She was occasionally used to ferry troops and aircraft to and from foreign deployments as well as participating in exercises. In 1951, she helped to transport troops to quell rioting in Cyprus after the collapse of the Anglo-Egyptian treaty of 1936. She was paid off in early 1955 and sold for scrap in late 1956.
Background and description
The Royal Navy's 1936 Naval Programme authorised the construction of two aircraft carriers. Admiral Sir Reginald Henderson, Third Sea Lord and Controller of the Navy, was determined not to simply modify the previous unarmoured design. He believed that carriers could not be successfully defended by their own aircraft without some form of early-warning system. Lacking that, there was nothing to prevent land-based aircraft from attacking them, especially in confined waters like the North Sea and Mediterranean. This meant that the ship had to be capable of remaining in action after sustaining damage and that her fragile aircraft had to be protected entirely from damage. The only way to do this was to completely armour the hangar in which the aircraft would shelter, but putting so much weight high in the ship allowed only a single-storey hangar due to stability concerns. This halved the aircraft capacity compared with the older unarmoured carriers, exchanging offensive potential for defensive survivability.Hobbs 2013, p. 83
Illustrious was in length overall and at the waterline. Her beam was at the waterline and she had a draught of at deep load. She displaced at standard load as completed.Friedman, p. 366 Her complement was approximately 1,299 officers and enlisted men upon completion in 1940.Hobbs 2013, p. 89 By 1944, she was severely overcrowded with a total crew of 1,997. After post-war modifications to convert her into a trials carrier, her complement was reduced to 1,090 officers and enlisted men.Lyon, p. 233
The ship had three Parsons geared steam turbines, each driving one shaft, using steam supplied by six Admiralty 3-drum boilers. The turbines were designed to produce a total of , enough to give a maximum speed of at deep load.Friedman, p. 134 On 24 May 1940 Illustrious ran her sea trials and her engines reached . Her exact speeds were not recorded as she had her paravanes streamed, but it was estimated that she could have made about under full power.Lyon, p. 235 She carried a maximum of of fuel oil which gave her a range of at or at or at .
The armoured flight deck had a usable length of , due to prominent "round-downs" at each end designed to reduce the effects of air turbulence caused by the carrier's structure on aircraft taking-off and landing, and a maximum width of . A single hydraulic aircraft catapult was fitted on the forward part of the flight deck. The ship was equipped with two unarmoured lifts on the centreline, each of which measured . The hangar was long and had a maximum width of . It had a height of which allowed storage of Lend-Lease Vought F4U Corsair fighters once their wingtips were clipped. The hangar was designed to accommodate 36 aircraft, for which of aviation spirit was provided.Brown 1977, p. 44; Friedman, p. 134; Hobbs 2013, pp. 84–85, 90
Armament, electronics and protection The main armament of the Illustrious class consisted of sixteen quick-firing (QF) dual-purpose guns in eight twin-gun turrets, four in sponsons on each side of the hull. The roofs of the gun turrets protruded above the level of the flight deck to allow them to fire across the deck at high elevations. Her light antiaircraft defences included six octuple mounts for QF 2-pounder ("pom-pom") antiaircraft guns, two each fore and aft of her island, and two in sponsons on the port side of the hull.Hobbs 2013, p. 85
The completion of Illustrious was delayed two months to fit her with a Type 79Z early-warning radar; she was the first aircraft carrier in the world to be fitted with radar before completion. This version of the radar had separate transmitting and receiving antennas which required a new mainmast to be added to the aft end of the island to mount the transmitter.Lyon, p. 227
The Illustrious-class ships had a flight deck protected by of armour and the internal sides and ends of the hangars were thick. The hangar deck itself was thick and extended the full width of the ship to meet the top of the 4.5-inch waterline armour belt. The underwater defence system was a layered system of liquid- and air-filled compartments backed by a splinter bulkhead.Friedman, p. 137; Hobbs 2013, p. 83
Wartime modifications While under repair in 1941, Illustriouss rear "round-down" was flattened to increase the usable length of the flight deck to .Friedman, p. 147 This increased her aircraft complement to 47 aircraft by use of a permanent deck park of 6 aircraft.Jones, p. 109 Her light AA armament was also augmented by the addition of 10 Oerlikon 20 mm autocannon in single mounts. In addition the two steel fire curtains in the hangar were replaced by asbestos ones.Friedman, p. 137; Hobbs 2013, p. 90 After her return to the UK later that year, her Type 79Z radar was replaced by a Type 281 system and a Type 285 gunnery radar was mounted on one of the main fire-control directors. The additional crewmen, maintenance personnel and facilities needed to support these aircraft, weapons and sensors increased her complement to 1,326.
During her 1943 refits, the flight deck was modified to extend its usable length to , and "outriggers" were probably added at this time. These were U-shaped beams that extended from the side of the flight deck into which aircraft tailwheels were placed. The aircraft were pushed back until the main wheels were near the edge of the flight deck to allow more aircraft to be stored on the deck. Twin Oerlikon mounts replaced most of the single mounts. Other twin mounts were added so that by May she had a total of eighteen twin and two single mounts. The Type 281 radar was replaced by an upgraded Type 281M, and a single-antenna Type 79M was added. Type 282 gunnery radars were added for each of the "pom-pom" directors, and the rest of the main directors were fitted with Type 285 radars. A Type 272 target-indicator radar was mounted above her bridge. These changes increased her aircraft capacity to 57Hobbs 2013, p. 91 and caused her crew to grow to 1,831.
A year later, in preparation for her service against the Japanese in the Pacific, one starboard octuple "pom-pom" mount, directly abaft the island, was replaced by two 40 mm Bofors AA guns.Friedman, p. 148 Two more twin Oerlikon mounts were added, and her boilers were retubed. At this time her complement was 1,997 officers and enlisted men. By 1945, accumulated wear-and-tear as well as undiagnosed shock damage to Illustriouss machinery caused severe vibrations in her centre propeller shaft at high speeds. In an effort to cure the problem, the propeller was removed, and the shaft was locked in place in February; these radical measures succeeded in reducing, but not eliminating, the vibrations and reduced the ship's speed to about .
Post-war modifications Illustrious had been badly damaged underwater by a bomb in April 1945, and was ordered home for repairs the following month. She began permanent repairs in June that were scheduled to last four months. The RN planned to fit her out as a flagship, remove her aft 4.5-inch guns in exchange for increased accommodation, and replace some of her Oerlikons with single two-pounder AA guns, but the end of the war in August caused the RN to reassess its needs. In September, it decided that the Illustrious would become the trials and training carrier for the Home Fleet and her repairs were changed into a lengthy refit that lasted until June 1946. Her complement was sharply reduced by her change in role and she retained her aft 4.5-inch guns. Her light AA armament now consisted of six octuple "pom-pom" mountings, eighteen single Oerlikons, and seventeen single and two twin Bofors mounts. The flight deck was extended forward, which increased her overall length to . The high-angle director atop the island was replaced with an American SM-1 fighter-direction radar, a Type 293M target-indication system was added, and the Type 281M was replaced with a prototype Type 960 early-warning radar. The sum total of the changes since her commissioning increased her full-load displacement by .Lyon, p. 221 In 1947 she carried five 8-barrel pom-poms, 17 Bofors and 16 Oerlikons. A five-bladed propeller was installed on her centre shaft although the increasing wear on her outer shafts later partially negated the reduction in vibration. While running trials in 1948, after another refit, she reached a maximum speed of from . Two years later, she made 29.2 knots from . At some point after 1948, the ship's light AA armament was reduced to two twin and nineteen single 40 mm guns and six Oerlikons.
Construction and service
Illustrious, the fourth ship of her name,Colledge, p. 170 was ordered as part of the 1936 Naval Programme from Vickers-ArmstrongsFriedman, p. 139 on 13 April 1937.Hobbs 2013, p. 84 Construction was delayed by slow deliveries of her armour plates because the industry had been crippled by a lack of orders over the last 15 years as a result of the Washington Naval Treaty. As a consequence, her flight-deck armour had to be ordered from Vítkovice Mining and Iron Corporation in Czechoslovakia. She was laid down at their Barrow-in-Furness shipyard two weeks later as yard number 732 and launched on 5 April 1939. She was christened by Lady Henderson, wife of the recently retired Third Sea Lord.Hobbs 2013, p. 90 Illustrious was then towed to Buccleuch Dock for fitting out and Captain Denis Boyd was appointed to command her on 29 January 1940.McCart, p. 11 She was commissioned on 16 April 1940 and, excluding her armament, she cost £2,295,000 to build.Lyon, p. 218