[Sailor Steve]

Food was rarely a problem. If a boat was lucky, torpedoes would run out long before supplies did. Without replenishing a Type VII boat was good for about 35 days, but once on station the boat could patrol at a slow speed and extend that by quite a bit. Later in the war there were supply ships available, but the real limiting factor was morale. Sooner or later crew efficiency is going to drop, especially in the cramped quarters of a German u-boat.