The Yamato class dominated the Japanese shipbuilding from 1935 through to the end of 1941. The 3rd member of the class, the Shinano, proceeded slowly till June of 1942 when the battle of Midway virtually wiped out the Japanese carrier divisions. More carriers were needed as a highest priority. The Shinano was to be converted to an aircraft carrier.
The third member of the Kanto class, the Amagi had been dropped down the priority list especially as the 14" guns they were to be armed with had proved ineffectual against the American battleships around Guadalcanal. To cure this problem the four twin 14" turrets were to be replaced with two of the spare triple 18" turrets from the Shinano. In the end the conversion work was still underway when Japan surrendered, but it is an interesting concept to see what it would have looked like.
The 18" guns fired a 3200lb shell, the 14" a 1600lb shell. Do the maths, 6x3200=19200, 8x1600=12800. Quite a large increase in broadside value. Of even more incalculable value is the amount of damage that the 18" shell will do to any ship it hits. No armour on an Allied battleship would be able to withstand the impact of one of these big boys.
As much as I like getting 18" guns to sea in this fashion. The Allied advantage in radar made these ships sitting ducks. They could not run during the day due to Allied air superiority and night fighting, which Japan was good at, was nullified by the Allied radar advantage. There would only ever be one end to these ships.
