Secondary batteries as insurance against close threats

How important was the secondary battery on a dreadnought-era battleship?

It was a necessary backup against destroyers and torpedo boats, especially where a fleet might face close attacks.

Early dreadnoughts carried little secondary armament, but the threat of torpedo craft made a defensive battery increasingly important in confined waters such as the North Sea. The role resembles close-in weapons on a modern aircraft carrier: the fleet should deal with the threat first, but the capital ship still needs a reserve defence. Early twentieth-century gunnery already followed this principle of layered protection.