A giant naval gun trades turret flexibility for a smaller hull

How small a ship could mount a 31.5-inch naval gun?

Possibly battlecruiser-sized if the gun fired along the hull, but a rotating turret would demand a much larger ship.

A 31.5-inch weapon could be mounted on a smaller ship only by giving up most turret flexibility. Aligning the gun along the hull would support its loads through the ship's length and make aiming depend largely on pointing the vessel. A battlecruiser-sized platform might then be conceivable, whereas a rotating turret would require a much larger hull. Mounting weight and recoil support, rather than calibre alone, determine platform size.