What would Yamato look like in an 18-inch treaty world?

What would Yamato look like if the earlier gun race had produced British 18-inch battleships?

The treaty system and subsequent building programmes would change so extensively that Yamato would be a fundamentally different design.

A Royal Navy already operating 18-inch capital ships at the end of the First World War would change the starting point for treaty negotiations. An 18-inch ceiling could replace the historical 16-inch baseline, with other navies wanting permission to build ships to match it. A later British reduction in calibre might then mean 16- or 16.5-inch guns, rather than the historical 14-inch choice. Yamato would emerge from such different assumptions that no simple modification of the historical design is offered. Italian Caracciolo plans would face a much stronger comparison, Germany's later battleships would struggle to compete, and the very large Tillman proposals would seem less exceptional.