The Royal Navy had several distinct 4.7-inch guns. The earlier 45-calibre Mark IX and XII family is the preferred starting point because it was already widespread, lighter, and available sooner for high-angle development. The later 50-calibre Mark XI brought greater range and power, but arrived with the L and M classes, required more fitting work, and offered fewer advantages for fleet-wide conversion. Development timing, mounting weight, training speed, and ammunition investment matter more here than calibre alone.
Chapter · 8:45-15:24
Choosing a 4.7-inch dual-purpose gun
The counterfactual begins by choosing the earlier 4.7-inch 45-calibre family, whose existing mounts offer a more practical route to high-angle fire than the later 50-calibre weapon.