All new German torpedoes were test-fired with dummy warheads six or more times by the Torpedoversuchsanstalt (torpedo inspectorate) to ensure they were in perfect working order before being issued to the U-Boat fleet. Even with this, torpedo failure rates were high.
Charles McCain is a Washington DC based freelance journalist and novelist. He is the author of "An Honorable German," a World War Two naval epic. You can read more of his work on his website: http://charlesmccain.com/ View all posts by Charles McCain