Vanguard's 5.25-inch guns and the 4.5-inch alternative

Why did the Royal Navy fit Vanguard with 4.5-inch guns instead of 5.25-inch guns?

The premise is corrected: Vanguard carried improved 5.25-inch mountings, although 4.5-inch commonality was debated.

Vanguard carried 5.25-inch guns, despite the question's premise and the initial answer accepting it. The correction identifies improved mountings that gave crews more workable space than earlier installations. The 4.5-inch alternative remained relevant because carriers used it and the 5.25-inch family was expected to end. Alex recalls debate about Anson and Howe as well as Vanguard, while automatic six-inch guns were still unavailable as a ready substitute. These proposed alternatives need to be kept separate from the armament actually fitted.