The King George V class added a third battleship gun caliber

Why was the King George V class armed with what some consider an inadequate 14-inch gun?

The 14-inch gun itself was sound. The objection is the extra wartime supply burden alongside the Royal Navy's existing 15- and 16-inch guns.

The 14-inch weapon was a sound gun. The preference for retaining 15- or 16-inch weapons rests chiefly on ammunition supply and standardization. Adding 14-inch guns meant that the Royal Navy had to support three battleship calibers during the Second World War. That fleet-wide burden is separate from the merits of the individual weapon.