Why the Weapon class retained twin 4-inch guns

Why did the Weapon class use twin 4-inch guns when 4.5-inch weapons were already appearing?

It was an intermediate wartime design using available equipment for air defence. The exact reason for choosing the 4-inch gun remains unresolved in this exchange.

The Weapon class used twin 4-inch guns while 4.5-inch weapons were becoming available elsewhere. It was an intermediate wartime design built around off-the-shelf equipment and a useful air-defence role, which explains the attraction of an available weapon even if a newer calibre offered another path. The detailed armament choice remains puzzling, so this exchange supplies procurement context rather than a fully documented design decision.