Design A-150 (1941)
The Imperial Japanese Navy was a major pioneer of warship gun calibers in the early 20th Century. In 1920, they commissioned the first dreadnought battleship to carry 16" guns: Nagato. In 1941, they followed up with the first, and only battleship class, to carry 18" guns in Yamato and Musashi. However, even before these two behemoths could commission, they planned to up the ante yet again. The A-150 design increased the displacement over the Yamato to 78,000 tons, but would likely have had only slightly larger dimensions. The biggest difference was in the armament. The fearsome 46cm (18.1") guns of Yamato were replaced with a main armament of six 51cm (20.1") guns in three twin turrets. This would have resulted in a broadside of 11,700kg (26,454 pounds), about halfway between the Iowa and Yamato classes, each of which had half again as many guns. The two ships of the class, Warships 798 and 799, were projected to be laid down in late 1941 or early 1942, and completed in 1946 or 1947. However, neither were ever laid down, as the IJN shifted construction focus to destroyers and carriers to replace its wartime losses.