[UKönig]

As far as realism goes, at least we don't have to maintain the equipment in the usual sense.
In peacetime/practice firing, recently manufactured torpedoes had always been used, and so the question of longevity never came up. But now it was discovered that after lying for a few weeks in a patrolling U-boat (with all the dampness, temperature variations, and crew knocking about), their functioning was further impaired. So, to add to all the existing burdens on the uboat captain, a new one was introduced, namely, to periodically regulate *all* torpedo mechanisms on board. In the case of those currently loaded in the tubes, this meant withdrawing them 3/4s back into the sub, recharging the batteries and checking the accuracy of their instruments, once every 48 hours (this was the procedure that the crew in "Das Boot" was doing, which earned Lt. Werner an oily rag in the face, when he got in their way).
Although these efforts did help reduce the number of torpedo failures, it was the early detonation of a torp fired by U39 at the aircraft carrier HMS Ark Royal, 150 miles west of the Hebrides, on Sept. 14 1939, responsible for the first U boat loss of the war...