From 4.5-inch to 5-inch naval guns

Is the Royal Navy moving from 4.5-inch guns to 5-inch?

Yes. The 5-inch has become the broader standard, while Britain is increasingly isolated as a 4.5-inch user.

The Royal Navy is expected eventually to move from 4.5-inch to 5-inch naval guns. Britain has become the principal remaining user of the older calibre while allied fleets have standardized elsewhere. Common ammunition, support, and development paths create a strong logistical and interoperability pull. Even a technically satisfactory national weapon can become uneconomic when its user base contracts.