How large would an Italian 18-inch-gun battleship need to be to retain the desired speed?
Short answerAbout Yamato size once the design also carries useful armour and the required machinery.
NotesArmament, armour, and speed are linked requirements rather than independent choices. An 18-inch gun installation alone does not determine the ship's displacement. Retaining useful protection while also reaching the speed expected of an Italian capital ship pushes the hull upward in size. Yamato provides the comparison point for how these demands combine into a very large battleship.