First fleet aircraft carrier to be completed after the outbreak of war, H.M.S. Illustrious, of 23,000 tons, was launched at Barrow in 1939. Her outstanding achievement, as flagship of Rear Admiral (now Admiral Sir Lumley) Lyster, was at Taranto on the night of November 11, 1940, when her Swordfish aircraft struck a crippling blow at the Italian fleet as it lay in harbour. The battleship Conte di Cavour sustained injuries from which she never recovered, and two other battleships were put out of action for some months.
While helping to escort a convoy to Malta in January 1941, the Illustrious became the target for six air attacks, in one of which 40 German dive-bombers secured a number of hits. On fire fore and aft and with her steering gear out of control, the carrier fought her way through to Malta, where temporary repairs were effected in spite of further air attacks. Ultimately she reached Alexandria and thence proceeded to the U.S.A. for refit.
Present during the occupation of Diego Suarez, Madagascar in 1942, and at the Salerno landings in 1943, the Illustrious went East again in 1944. She took part in a surprise raid on enemy airfields in Northern Sumatra in April of that year, and a month later was concerned in a similar raid on the naval base at Surabaya, Java. In June targets for her aircraft were at Port Blair, in the Andaman Islands, followed by a successful attack on the port of Sabang, Sumatra, on July 25. In the early months of 1945 she was one of the carriers whose aircraft wrecked oil refineries in Southern Sumatra; and in the attack on the Saki group of the Ryukyu Islands, south-west of Japan, she wore the flag of Vice-Admiral Sir Philip Vian. On this occasion she was narrowly missed by Japanese suicide aircraft.