An old cruiser makes convoy attacks costly

Eight or ten quick-firing 4.5-inch guns would make a converted cruiser dangerous to destroyers and useful against aircraft. Light-cruiser protection makes it harder to eliminate than a destroyer, while torpedoes can end a commerce raider's cruise even if the old ship cannot win a conventional gun duel. Depth charges and anti-aircraft weapons give the escort value against submarine and air attack as well. A raider must therefore bring a 6- or 8-inch-gunned cruiser through an aggressive destroyer screen before reaching the transports. An obsolescent hull protects a convoy by imposing risk, dividing the attacker's fire, and threatening damage the raider cannot afford.