Heavy fleet units answer the surface-raider threat

Convoy protection required more than local escorts. In a modern comparison, an escort carrier's aircraft mix might include anti-submarine helicopters, airborne early-warning helicopters, or fighters according to the threat. Sloops and corvettes could fire back if caught by a surface raider, but they were unlikely to defeat a dedicated warship unless a converted merchant raider was caught at an exceptional disadvantage. Destroyers, cruisers, battleships, and fleet carriers supplied the heavier counterweight. The resulting task group was layered by purpose rather than built from identical ships. Force design had to cover more than the submarine threat because an enemy could choose another form of attack.