Radar and radar control were improving, but aircraft could still be detected accurately only at comparatively close range. A large gun's nominal range and rate of fire meant little if the mount could not train, settle, and begin accurate fire before an attacker arrived. Faster-moving 40 mm mounts could bear on a new target sooner and put up a useful volume of fire in the available seconds. The same selection logic led the Royal Navy to choose the heavily gunned 1936 Tribal class for the 10th Destroyer Flotilla's Channel fighting against German E-boats and destroyers. That short engagement window made the medium anti-aircraft battery the practical core of Battle-class air defence rather than a secondary supplement.
Notable Point · 30:01-31:53
Why 40 mm mattered to air defence
The Battle class carried many 40 mm weapons because close-range air defence depended on rapid tracking, traverse, and volume of fire as much as gun calibre.