Britain used 14-inch guns as a treaty signal

Why did the Royal Navy buy a 14-inch Vickers gun instead of retaining 15-inch weapons?

Britain wanted its own 14-inch battleships to demonstrate the gun-calibre limit it was asking other naval powers to accept in treaty negotiations.

The Royal Navy already used the larger 15-inch calibre when it bought the 14-inch Vickers weapon. Treaty diplomacy was the deciding factor. By ordering battleships with 14-inch guns, Britain could present its own procurement as an example for other powers during naval-arms negotiations. The choice therefore served as a bargaining signal as well as an armament decision, continuing a policy already visible in cancellations before the Washington conference.