What the 1920s Royal Navy should stockpile for the next war

If the 1920s Royal Navy could stockpile one component for the Second World War, what should it choose?

Durable gun barrels or completed heavy turrets are strongest choices because they remain useful and accelerate wartime construction or standardization.

One proposal is a large reserve of 40 mm pom-pom barrels and ammunition, whose basic utility survives the interwar period. Another is completed heavy-gun turrets, especially triple mountings able to accept 15-inch weapons, because turret manufacture is a major bottleneck in battleship construction. Stored mounts could enable faster Vanguard-like ships or alter the King George V design toward twelve 15-inch guns. A third option is standardized 4.7-inch weapons to reduce the wartime mixture of medium-caliber ammunition. The panel rejects stockpiling 1920s propellant because rapid chemical development in the 1930s would leave it obsolete. The useful criterion is whether the part remains compatible and removes a future industrial bottleneck.