Good question I think.
What was the date/year?
I have had 4 out of 5 "duds" on a Type IIB in September '39
Me I consider this failure a function of the "dud" and consider it part of the modelling of a dud. I appreciate that "dud" means to many of us a failed detonation.
Might be better if they called it failed torpedo option for clarity. But it happens, failed torpedos...