Why spare 15-inch turrets defined HMS Vanguard — Bruships 146: Naval History Questions, Boxes Getting Packed… at 37:22

Why spare 15-inch turrets defined HMS Vanguard

Vanguard's 15-inch battery was a shortcut made possible by spare naval turrets; an 18-inch alternative required an entirely different supply of sea-going mounts, barrels, and follow-on class plans.

Question

Could Britain have built Vanguard with 18-inch guns if enough large turrets existed?

Short answer

Only with enough purpose-built naval turrets, barrels, and follow-on equipment for a class; spare 15-inch mountings were what made Vanguard the quick practical design.

Notes

HMS Vanguard was built around available 15-inch guns and turrets because this offered the fastest route to a completed battleship. Eighteen-inch weapons placed ashore would not automatically solve the problem, since land mountings can use greater elevation and bedrock support while ship turrets must function on a moving hull. A one-off four-turret ship would also need spare barrels and a navalized mounting design. Vanguard was intended as the first of a class, so the industrial requirement extended beyond one set of eight guns.