Troopship routing versus the commerce war

Sims explains why Germany could not simply redirect the U-boat campaign toward American troopships. The transports could approach Europe across roughly 1,400 nautical miles, receive new wireless orders, and unload at different ports when submarines appeared. Concentrating U-boats on a few guessed routes would also reduce pressure on the merchant tonnage that sustained the Allied war. The United States nevertheless lacked enough destroyers to escort every returning transport, so empty ships sometimes crossed the danger zone under armed-yacht escort or alone to preserve turnaround time. Sims records five returning transports torpedoed, of which three were sunk. Convoy protection depended on geography, intelligence, scarce escorts, shipping tempo, and competing strategic objectives.