In keeping with longstanding Japanese naval strategy, the A-150s would have carried six 51-centimeter (20.1 in) guns to ensure their qualitative superiority over any other battleship they might face.

The extensive distances involved, and the likelihood of this expansion leading to a confrontation with the United States, led the Japanese to build and maintain a large fleet that could seize and hold onto these territories.

[5] The Imperial Japanese Navy had recognized since at least 1896 that the country could not outproduce its potential opponents, and therefore insisted that its ships had to be more powerful than foreign equivalents.

They initially focused on a ship closer to the displacement of the preceding Yamato class, on which plans had just been completed, albeit one mounting six 51-centimeter guns.

These would have been the largest ever fitted to a capital ship, dwarfing the 46-centimeter guns mounted on the Yamato class,[13] and were a key factor in naval historians William H. Garzke and Robert O. Dulin's argument that the A-150s would have been the "most powerful battleships in history".

[1] Construction of two of the 51-centimeter guns was ordered in 1941 for trials at the Kure Naval Arsenal and detailed designs of their turrets were drawn up.

Historians Eric Lacroix and Linton Wells have written that Japanese designers were considering mounting a large number of 65-caliber 10-centimeter (3.9 in) Type 98 dual-purpose guns, though this was not final.

They fired 13-kilogram (29 lb) projectiles at a muzzle velocity of 1,030 m/s (3,400 ft/s), although resulting wear on the barrels reduced their designed lifespan to only about 350 rounds.