Eighteen-inch battleships and twelve-inch cruisers

If 18-inch guns become the upper limit, do battlecruisers or large cruisers appear before the Second World War?

The category could shift toward 12-inch-gun large cruisers, with treaty definitions and the retention of older battlecruisers changing around the larger battleship standard.

Ship categories depend on the standards around them. If 18-inch guns become the battleship norm, a 12-inch armed ship becomes a more plausible large cruiser instead of an obvious capital ship. The Washington Treaty might then define a separate large-cruiser category. Britain might also retain older 12-inch battlecruisers longer or reduce the armament of 13.5-inch ships while replacements are built.