Nelson gun logistics and the F3 design boundary

The Nelson class's separate 16-inch ammunition supply imposed a fleet-wide logistical cost. A new 15-inch/50-calibre gun could also have supported upgrades to existing 15-inch ships, although treaty displacement and British dry-dock limits constrained the alternatives. Greater internal subdivision is the preferred survivability improvement here before a thicker belt. F3 and F2 sit around the emergence of the phrase "fully armoured battlecruiser" in Royal Navy design discussion, although some sources appear to apply the term retrospectively. The phrase describes an approach toward the fast battleship from the battlecruiser side. Armour thickness alone does not complete that transition: the extent of armour coverage and the subdivision behind it also matter. Two ships with equally thick belts can therefore have substantially different protection.