The alternate history requires a 1935 service-ready gun

The Tribal design was effectively locked in during 1936, while the historical 4.5-inch weapon did not enter service until later. Because the Royal Navy preferred proven weapons for destroyers, the scenario needs development to begin around 1932-33 and yield an in-service system by 1935. Third Sea Lord Reginald Henderson could make that timetable plausible by concentrating resources on the project earlier. The existing 4.7-inch mounting remained the baseline because it was proven, met the period's all-round requirements, and allowed eight guns within the chosen displacement. The counterfactual begins with a change in administrative priority and development timing before it reaches the destroyer's physical design.