How swarm size changes a ship's gun-defence problem

Are additional gun defences against USVs an excessive response to a secondary threat?

The reply treats mass attack as the relevant threat: larger swarms justify more defensive weapons, while several defending ships also increase the attacker's requirement.

A single USV is presented as a target for a destroyer's main gun. The discussion then moves through illustrative attacks by 20 or 30 craft and larger groups of 50, 60, or 70. More simultaneous threats increase the usefulness of 76 mm guns and separate defensive mounts alongside the main weapon. Several warships operating together can contribute their weapons to the defence, so the size of the defending formation also matters. The figures illustrate the argument about mass and defensive layers.