How secondary guns changed after Dreadnought

Pre-dreadnought secondary guns could be the principal weapons expected to destroy an opponent, while the arrival of effective heavy guns changed the main battery into the primary killing system. Smaller guns then became more specialized, particularly for defeating torpedo boats and destroyers before they could approach. Rapid fire could smother lightly protected attackers, disable exposed crews, and produce a mission kill before a torpedo attack developed. The point is functional rather than semantic: calibre choices reflect the targets a ship is expected to handle and the tactical problems its designers expect it to face.