The 5.5-inch gun served on Hood and HMS Eagle and was considered a powerful destroyer weapon, but treaty limits on ship size worked against that option. The 5.25-inch gun equipped Dido-class cruisers and capital ships as a dual-purpose weapon and was also considered for destroyers. By the Second World War, the Royal Navy had four service variants of the 4.7-inch gun, three of the 4.5-inch gun, and two of the 4-inch gun. Each represented an attempt to establish a useful fleet standard. Supporting the resulting variety required attention to individual variants as well as calibre.
Notable Point · 2:12-3:20
Why one gun calibre did not guarantee one fleet standard
British armament proposals covered several calibres, while individual calibres also accumulated different service variants.