They didn't.
That's the short answer.
Neither U-boat captains nor US submarine commanders had the tools or the time and expertise to investigate torpedo failures. They reported the failures, along with all available data on the circumstances surrounding the failures, to "higher authority". It was the responsibility of "higher authority" to do the investigations and fix the problems.
What you will find is that the "higher authority" in both navies failed miserably to do their job. They refused to believe there was anything wrong with the torpedoes, they blamed the captains/crews for the failures.
In both navies, the problems were finally addressed and fixed only after the operational commanders (BdU and COMSUBPAC) insisted the submarine skippers were right. There was overwhelming evidence that there were problems with torpedoes that the technical authorities needed to investigate and resolve. A(nother) perfect example of bureaucratic arrogance.
|