The German targets were merchant hulls, and capital-ship secondary batteries offered a fast, economical way to sink them without relying on main-battery fire. A surface-raider threat therefore forced Britain to place scarce capital ships alongside vital convoys. Those escorts then had to match merchant speed and a constrained route through submarine hunting grounds. A battleship protected the convoy from Scharnhorst and Gneisenau but surrendered much of its freedom of maneuver against U-boats. Surface and undersea threats could thus amplify one another even without a surface battle.
Chapter · 56:40-58:27
Surface raiders turned convoy protection into a two-threat problem
Capital-ship secondary guns could destroy merchants efficiently, while the battleships assigned to deter them became constrained targets in U-boat waters.