Interwar exercises created confirmation bias: aircraft concentrated on capital ships, so escorting destroyers appeared to need only low-angle fire across the formation. The Air Ministry's emphasis on level bombers reinforced that picture. When a British five-inch programme failed, attention turned to replacing the four-inch AA gun with a 4.5-inch weapon, which was subsequently expanded into a universal dual-purpose system. Earlier investment in the established 4.7-inch 45-calibre family could have challenged that institutional path before it hardened.
Chapter · 17:47-22:13
How interwar doctrine left 4.7 inch low-angle
Exercise assumptions and the expected bomber threat preserved the 4.7-inch gun as a low-angle destroyer weapon while the 4.5-inch programme grew from replacing four-inch AA guns.