Why the Royal Navy fielded so many gun calibres

Why did the Royal Navy retain several intermediate gun calibres instead of standardizing on 5- and 14-inch weapons?

Existing industrial support favored the proven 13.5-inch gun, while changing tactical requirements and funded development programs repeatedly shifted the preferred secondary and destroyer calibre before the 4.5-inch emerged as a practical dual-purpose standard.

The Royal Navy's 13.5-inch battleship gun had already proved itself and came with a working industrial and logistical base. Moving half an inch to 14 inches offered little enough gain that the navy preferred its established weapon and the room for later escalation created by one-and-a-half-inch calibre steps. The secondary and destroyer calibres multiplied for a different reason. Each standardization attempt began under a different tactical priority: four inches for high-angle anti-aircraft fire, heavier weapons such as the 4.7-inch for anti-ship work, and intermediate guns for a dual-purpose compromise. The 4.7-inch could have become the common weapon for destroyers and smaller ships, but its anti-aircraft development arrived late. Sustained work and carrier service instead made the 4.5-inch the practical winner, while tighter budgets kept the US Navy focused on successive five-inch guns.