The class's main job was escort protection against submarines and aircraft; destroyers with torpedoes and accompanying cruisers were expected to handle major surface threats. The 4-inch battery still had a practical anti-surface role because its high-explosive shells could defeat merchant auxiliaries and other lesser opponents. Auckland would not have been a match for Admiral Graf Spee. Paired with a cruiser, however, a sloop could search a wider area, deal with a raider's support ship, or radio a sighting before being overtaken. A modest escort could extend a scarce cruiser's reach without being its equal in combat.
Notable Point · 11:13-13:33
Why an anti-aircraft sloop still carried a surface-fighting battery
The Egrets were meant to defend convoys from aircraft and submarines, while their 4-inch guns could still deal with smaller raider-support vessels.