Why the Royal Navy moved toward a five-inch gun

Would an earlier British twin five-inch gun have prevented today's move to a five-inch weapon?

Probably; the present change is driven largely by ammunition logistics and interoperability, tempered by industrial-sovereignty concerns.

Had Britain completed the earlier twin five-inch/70 weapon, the panel sees little reason to adopt a new five-inch system now. The present move reflects the isolation of the 4.5-inch calibre: British ammunition production ceased in 2016 even though barrel-making capacity remains. A five-inch weapon connects the fleet to a much wider ammunition and supplier base, including specialised rounds. Strategic independence could still justify reviving or retaining domestic capability rather than treating interoperability as the only goal. The closing discussion considers a possible BAE-OTO Melara partnership and an unresolved choice between a new five-inch gun and a larger six-inch system.