Preliminary work for a new design began in 1944 and continued for the next year or so until the RN realised that they were unaffordable in the post-war financial environment.

The treaty contained an "Escalator Clause" that would increase the maximum allowable calibre to 16 inches if the Japanese government failed to sign; this was triggered in April 1937.

Maintaining the same speed, protection, and secondary armament as the older ships while using 16-inch guns proved impossible while remaining within the treaty limits.

In an effort to remain within treaty limits, the overall weight of armour was slightly reduced and two twin 5.25-inch (133 mm) gun turrets as well as aircraft and their facilities were eliminated.

[3] The Admiralty in any case decided to limit itself to 40,000 long tons and nine 16-inch guns on the grounds that larger vessels would be unable to dock at the major Royal Navy dockyards at Rosyth or Portsmouth.

[6] The appearance of the Lions closely resembled that of the KGVs, but included a transom stern to improve steaming efficiency at high speed.

[8] In the interests of saving time, the four-shaft unit machinery design from the KGVs was duplicated with alternating boiler and engine rooms.

[10] The Lion-class ships' main armament consisted of nine newly designed 45-calibre BL 16-inch Mark II guns in three hydraulically powered triple-gun turrets.

The waterline belt was intended to be made from Krupp cemented armour (KCA) 14.7 inches (373 mm) thick and was 433 feet (132 m) long.

The KCA face-plates of the main gun turrets were intended to be 15 inches thick and their roofs would have used 6-inch (152 mm) non-cemented armour plates.

[7] Intended to resist the impact of a 1,000-pound (450 kg) armour-piercing bomb dropped from a height of 14,000 feet (4,300 m), the Lions' deck protection was identical to that of the KGV class.

Both of the inner and outer voids were fitted with pumps to flood them with water to level the ship (counter-flood) in case she began to list.

The beam increase meant that many of the Royal Navy home docking facilities, including Rosyth and Portsmouth, could no longer accommodate these ships.

The requirement that 'A' turret had to be able to fire directly ahead at 0° elevation was rescinded as it radically reduced freeboard forward and caused the KGVs to take a lot of water over the bow in head seas.

The 4,800 long tons (4,877 t) of fuel increased their endurance to an estimated maximum of 16,500 nautical miles (30,600 km; 19,000 mi) at a speed of 10 knots.

Because the light cruiser Belfast lost all steam power when she struck a mine early in the war, two diesel generators were substituted for two turbo-generators.

[19] The RN's Plans Division set a requirement for a dozen battleships for the post-war navy and the DNC began another design in February 1944 that would incorporate wartime lessons, but they soon concluded that "the power of modern weapons had increased so much that ever-increasing armour and torpedo protection was required until it became incompatible with the limited offensive power of the ship.

This design was too large, so multiple variants were considered over the next several months, examining the effects of reducing side armour, underwater protection and the number of main and secondary gun turrets.

The provisional staff requirements were issued in March and increased the speed to 29 knots (54 km/h; 33 mph) and set the endurance equal to that of the original design, which was slightly modified in April as 'Design B'.

The most radical variant, christened 'Design X', had an armour arrangement similar to the modernised battlecruiser Renown with a pair of 16-inch and eight 4.5-inch turrets and had only minimal underwater protection, relying on tight compartmentalisation and strengthened internal bulkheads to localise damage.

The DNC asked permission to investigate further methods of reducing the size of 'B3' in July and work continued on both designs through October.

[22] On 8 January 1941, Rear-Admiral Bruce Fraser, Third Sea Lord and Controller of the Navy, asked the DNC to work up a hybrid aircraft carrier based on the Lion-class hull.

The machinery was unchanged, but another 600 long tons (610 t) of oil increased her endurance to 14,750 nautical miles (27,320 km; 16,970 mi) at 10 knots.

Lion was laid down at Vickers' Walker, Newcastle upon Tyne shipyard on 4 July; Temeraire preceded her at Birkenhead on 1 June.