Royal Navy analysis of First World War experience and interwar exercises expected cruiser actions near 15 kilometres and compared performance at about 18 kilometres. In ten minutes, the study estimated 936 rounds for a twelve-gun Town and 392 for an eight-gun County. At the illustrative rate of one hit per twenty rounds, that becomes roughly 46 or 47 Town hits against 18 or 19 County hits. An 8-inch shell was heavier and more penetrative, but the Town could put far more rounds toward a maneuvering target in poor conditions. The ten-minute interval reflected the bursts of sustained fire expected in chases, withdrawals, and other cruiser actions. A Tribal destroyer and the first Crown Colony batch could match the Town's round count, though their different shell weights changed the effect. The Dido delivered substantially less total shell weight despite its reputation as a machine-gun cruiser.
Chapter · 18:05-23:55
Why twelve 6-inch guns beat fewer 8-inch guns in the study
Royal Navy cruiser studies favoured rapid 6-inch fire because maneuvering combat at about 18 kilometres rewarded repeated chances to hit during a ten-minute burst.