Convoys shrink the ocean NATO must defend

The convoy system does more than reduce the number of isolated targets. It concentrates the merchant ships so that escorts need to control only the water around one moving formation. Helicopters, patrol aircraft, and surface sensors can then build overlapping searches instead of hunting across the whole Atlantic. Soviet submarines must approach that defended area to reach the cargo ships, turning the convoy itself into a way of drawing attackers toward NATO's anti-submarine forces.