HMS Indefatigable was one of two Implacable-class aircraft carriers built for the Royal Navy (RN) during World War II. Completed in 1944, her aircraft made several attacks that year against the German battleship Tirpitz, inflicting only light damage; they also raided targets in Norway. The ship was transferred to the British Pacific Fleet (BPF) at the end of the year and attacked Japanese-controlled oil refineries in Sumatra in January 1945 before joining the American forces in March as they prepared to invade the island of Okinawa in Operation Iceberg. Indefatigable and the BPF joined the Americans in attacking the Japanese Home Islands in July and August. Following the end of hostilities she visited ports in Australia, New Zealand and South Africa.

After returning to the UK in early 1946, Indefatigable was modified for transport duties, and ferried troops and civilians for the rest of the year before she was reduced to reserve. She was recommissioned in 1950 as a training ship for service with the Home Fleet Training Squadron, participating in exercises and making several port visits overseas. The Board of Admiralty decided that she was redundant in early 1954 and decommissioned her later that year. Indefatigable was sold for scrap the following year, and scrapped between November 1956 and April 1959.

The Implacable class were ordered under the 1938 Naval Programme by the Chamberlain government as part of the general rearmament begun in response to the rise of Nazi Germany and Fascist Italy. The design originated as an improved version of the Illustrious-class aircraft carriers and was intended to be 2 knots (3.7 km/h; 2.3 mph) faster and carry an additional dozen aircraft over the 30-knot (56 km/h; 35 mph) speed and 36 aircraft of the earlier ships. To remain within the 23,000 long tons (23,000 t) limit allowed by the Second London Naval Treaty, these improvements could only be made by reducing armour protection. Indefatigable was 766 feet 6 inches (233.6 m) long overall and 730 feet (222.5 m) at the waterline. Her beam was 95 feet 9 inches (29.2 m) at the waterline, and she had a draught of 29 feet 4 inches (8.9 m) at deep load. The Implacable-class ships were significantly overweight and displaced 32,110 long tons (32,630 t) at deep load. The ships had metacentric heights of 4.06 feet (1.2 m) at light load and 6.91 feet (2.1 m) at deep load as completed. Indefatigable's complement was approximately 2,300 officers and ratings in 1945.

The ships had four Parsons geared steam turbines, each driving one shaft, using steam supplied by eight Admiralty 3-drum boilers. The turbines were designed to produce a total of 148,000 shaft horsepower (110,000 kW), enough to give the Indefatigable-class ships a maximum speed of 32.5 knots (60.2 km/h; 37.4 mph). On sea trials, Indefatigable reached a speed of 32.06 knots (59.38 km/h; 36.89 mph) with 150,935 shp (112,552 kW). She carried enough fuel oil to give her a range of 6,900 nautical miles (12,800 km; 7,900 mi) at 20 knots (37 km/h; 23 mph).

The 760-foot (231.6 m) armoured flight deck had a maximum width of 102 feet (31.1 m). A single hydraulic aircraft catapult was fitted on the forward part of the flight deck. The Implacable-class carriers were equipped with two lifts on the centreline, the forward of which measured 45 by 33 feet (13.7 by 10.1 m) and served only the upper hangar, and the aft lift (45 by 22 feet (13.7 by 6.7 m)), which served both hangars. The upper hangar was 458 feet (139.6 m) long and the lower hangar was 208 feet (63.4 m) long; both had a maximum width of 62 feet (18.9 m). Each hangar had a height of only 14 feet which precluded storage of Lend-Lease Vought F4U Corsair fighters as well as many post-war aircraft and helicopters. Designed to stow 48 aircraft in their hangars, the use of a permanent deck park allowed the Implacable class to accommodate up to 81 aircraft. The additional crewmen, maintenance personnel and facilities needed to support these aircraft were housed in the lower hangar. The ships were provided with 94,650 imperial gallons (430,300 L; 113,670 US gal) of aviation gasoline.

The ship's main armament consisted of sixteen quick-firing (QF) 4.5-inch (114 mm) dual-purpose guns in eight twin-gun turrets, four in sponsons on each side of the hull. Unlike the Illustrious-class ships, the roofs of the gun turrets were flat and flush with the flight deck. The gun had a maximum range of 20,760 yards (18,980 m). Indefatigable's light anti-aircraft defences included five octuple mounts for QF 2-pounder ("pom-pom") anti-aircraft (AA) guns, two on the flight deck forward of the island, one on the aft part of the island, and two in sponsons on the port side of the hull. A single quadruple 2-pounder mount was also fitted on the port side of the hull. The 2-pounder gun had a maximum range of 6,800 yards (6,200 m).

The ship was also fitted with 55 Oerlikon 20 mm autocannon in 17 single and 19 twin-gun mounts. These guns had a maximum range of 4,800 yards (4,400 m), but some were replaced by 40 mm Bofors AA guns when the ships were transferred to the Pacific Theatre as the 20 mm (0.79 in) shell was unlikely to destroy a kamikaze before it hit the ship. The Bofors gun had a maximum range of 10,750 yards (9,830 m). By August 1945, Indefatigable had 10 single Bofors guns, plus 14 twin and 12 single Oerlikon mounts. By April 1946 these had been reduced to 11 Bofors guns, 6 twin and 7 single Oerlikon guns.

Details of the Implacable-class ships' radar suite are not readily available. They were fitted with the Type 277 surface-search/height-finding radar on top of the bridge and a Type 293 target indicator radar on the foremast. Victorious, one of the Illustrious-class ships upon which Indefatigable's design was based, also carried Type 279 and Type 281B early-warning radars. Type 282 and Type 285 gunnery radars were mounted on the fire-control directors.