A British 5.5-inch dual-purpose gun path

The Royal Navy's existing 5.5-inch gun provides a practical comparison for the American 5.4-inch proposal. A more advanced dual-purpose version was considered around the G3, N3, F3, and Nelson design work as a possible replacement for separate 6-inch and lighter anti-aircraft batteries. Larger ships could carry powered handling and enough crew support to sustain a useful rate of fire, while destroyers faced much sharper penalties in space, personnel, water, and electrical demand. If adopted, the calibre might displace the later 5.25-inch gun on capital ships and carriers while leaving 4.5-inch development concentrated on destroyers. The counterfactual also asks whether 5.5-inch weapons could reshape treaty-cruiser categories and permit denser turret arrangements, while acknowledging that a dual-purpose quadruple mounting would be technically difficult.