How four-inch guns turned destroyers into air-defence escorts

What made some Royal Navy destroyers anti-aircraft destroyers?

An all-four-inch main battery was a strong indicator that the destroyer had been configured for anti-aircraft work.

Gun calibre can give a quick guide to a destroyer's intended role. Some L- and M-class ships and other destroyers received all-four-inch main batteries. That arrangement emphasized high-angle anti-aircraft fire and made them specialized air-defence destroyers. The distinction helps readers see how ships of the same broad type could be adapted for different fleet tasks.