The Germans, just the Americans, had issues with torpedo failures early in the war. Both nations (and others) had issues with the "magnetic" pistols failing to properly detect and detonate, but they also had issues with running depth, in that when the torpedoes were tested, "practice" head were used to make adjustments. Once a warhead was fitted on the torpedoes, they ran deeper than set. There was a plethora of troubles...
http://www.uboataces.com/articles-wo...orpedoes.shtml
https://digitalcommons.georgiasouthe...99&context=etd