British gun standardization and destroyer size

Why did Britain use so many different capital-ship and dual-purpose guns instead of standardizing on weapons such as 15-inch and 4.7-inch guns?

Treaty politics, continuing tests and changing requirements drove gun development. Early standardization might instead have produced a developed 5.5-inch gun and much larger destroyers.

The proposed 15-inch/50 gun never entered service. Treaty politics drove the changes between 16-inch Nelson and Rodney guns, the 14-inch King George V class, and renewed 16-inch work for the Lions. Continued funding and testing also kept moving the preferred smaller-gun standard before an earlier choice had spread across the fleet. Standardization in the F3 design period could instead have selected a 5.5-inch gun, followed by twenty years of development rather than retention of the unchanged 1920s weapon. The panel debates whether that would push destroyers toward 3,000 tons and require changes to treaty limits. A 3,000-ton destroyer with eight 5.5-inch guns would then complicate the case for a 10,000-ton cruiser with only eight 6-inch guns.