G3 battlecruisers with 16.5-inch guns before the Washington Treaty

A 16.5-inch battleship gun is favoured here for a somewhat heavier shell while retaining the firing rate associated with sixteen inches, with little advantage expected from a further jump to eighteen inches. Late World War I gun designs provide examples reaching 16.5 inches and fifty calibres in barrel length. The counterfactual assumes Britain completes the G3 battlecruisers quickly and keeps their 16.5-inch guns. It omits the reduction to sixteen inches described as an attempt to anticipate Washington Treaty gun limits, while noting that a tonnage limit would also become a problem. The possible outcome leaves Britain with 16.5-inch weapons and the United States and Japan with sixteen-inch guns. Existing effective sixteen-inch armament would make the small increase difficult to justify economically. An imagined exchange with Congress tests that funding argument. The scenario distinguishes a preference when designing a new gun from a sufficient reason to replace equipment already available.