During the 1936 London Naval Treaty discussions, Britain insisted upon fourteen-inch guns as the maximum sized armament for battleships, but the Japanese delegation balked and succeeded in having the 16-inch clause retained (historically true, but in "Grand Fleet", even while scheming to build the 18-in gunned Kii!). The subsequent King George V class of dreadnoughts complied fully with the Washington Naval Treaty limits of 35,000 tons standard displacement, and the fourteen-inch gun in quadruple turrets was selected for the main armament partially as an example to the world that bore size needn't be increased to the Treaty's 16-inch limit to have a fine battleship. Three such turrets, a superfiring pair in front and a single in the stern, were initially envisioned, but stability concerns, magazine protection, and weight limits relegated the forward superfiring turret to a twin instead of a quadruple. Protection was world-class at the time and speed was modest, but faster than the Royal Navy's World War one leftovers. Several of this class were designed and built for the new Royal Navy. Once the original Treaty had expired it seemed that the world was not impressed by Britain's self-restraint in size and caliber, and if Britain were not to fall behind, something would have to change.

Increasing hostility in the Far East, where Japan had dreadnoughts both powerful and fast, created some urgency in getting a more formidable, even faster warship than the KGV's out to help defend Singapore and other British interests. The sixteen-inch rifles that were to go on the new Lion class of battleships suffered design problems, and was going to delay completion of the ships. Two plans were envisioned: one in which four old, spare twin 15-inch gun turrets could be dropped into a new 45,000-ton ship (Vanguard project); or one in which the four quadruple turrets earmarked for the last two of the KGV series (Anson and Howe) might be incorporated into one mighty, slightly faster super-dreadnought of some 52,000 tons (extra length and additional boilers for added speed added a distinctive third funnel). The two leftover twin fourteen-inchers might be allocated to a large cruiser somewhat like the Glorious light battlecruisers, only faster and better protected. A new generation of advanced gun-control radar gave increased accuracy, and a new super-heavy armored projectile promised increased penetration to compete with the larger-bored guns of her potential adversaries.

Laid down just as the war started, progress on this leviathan (Britain's largest warship ever) and her cruiser cohort were stalled a bit to hurry the effort to put the KGV class ships currently on the ways into the water. The problems with the 16-inch guns of the Lion class were also solved more quickly than expected and even they would most likely beat the new super-battleship to the water. The name "Magnificent" was going to be applied to a light fleet carrier then under construction, but "Gun Club" proponents wanted a name to match previous giant gunships (Incomparable or Superb) and they prevailed. Singapore fell before the now-named Magnificent was completed. She would be the last and best battleship ever built for the Royal Navy.

Magnificent was escorting Arkangelsk-bound convoys when the German battlefleet made its last great sortie into the North Sea, so she missed out on one of the few opportunities to prove herself. She went to the Far East with the fast carrier Malta, but she suffered a collision with another warship and her hastily-repaired hull was badly torqued in a Pacific typhoon's rough seas. She ended up spending considerable time in port instead of meeting the Japanese giants in battle. Regarded as a "white elephant" by the Admiralty, Magnificent was broken up for scrap shortly after the War ended.