The 300-boat claim depends on how many wolfpacks would actually find a convoy, how many could attack effectively, and how many boats would be lost. A slow convoy might be vulnerable, but the Royal Navy and its allies could adjust escort numbers, routing, and tactics. Escorts could also be reinforced once signals traffic revealed which convoy a pack was hunting. Even when Germany had more than 400 submarines, only a fraction were operational in the Atlantic and Operation Torch still went ahead.
Chapter · 2:27:40-2:32:39
Why 300 U-boats would not win the Atlantic
Dönitz's famous 300-submarine requirement overlooks convoy routing, escort adaptation, operational losses, and competing theatres.