N3 gun caliber and an unknowable service history

Would twelve 16- or 16.5-inch guns have been better than nine 18-inch guns for the N3?

Possibly, but the unbuilt design leaves too little operational evidence for a confident judgment.

A firm verdict is impossible because neither the N3 nor its 18-inch weapons produced operating experience. The question pits the volume of fire from twelve 16- or 16.5-inch guns against nine heavier 18-inch weapons, but the actual result remains unknowable. The N3s appear as heavy bastions at the head of a thunderous British battle-line hammer. How the guns and ships would have behaved in service remains counterfactual, so any confident answer would overstate the evidence.