[banryu79]

Originally Posted by GJO

What is not established, so far, is the impact that high waves (the typical "North Atlantic Rollers") had on torpedo failure.

I haven't the slightest idea about how much the "wave factor" coud determine a torpedo failure (in the broadest sense: either determining a premature detonation or causing the torpedo to miss the target). The thesis linked by Warren Peace doesn't quantify this aspect.

But reading that it is clear that the main culprit of the crappy performances of early war torpedoes was the pistol (both AZ and MZ aka impact & magnetic, each one in its specific way).

Just to sum up things for readers of this thread that do not want to read the whole thesis to dig up some statistics, I report them here:

During this time from the middle of November 1939 to June 12, 1940, the Uboats had fired a total of 531 torpedoes equipped with the Pi A+B pistol. Of the 531 torpedoes a total of 440 employed the magnetic setting. Ofthese, forty-three torpedoes (9.8%) were categorized as “self-detonators.” Nine torpedoes (2.0%) were “early detonators.” Sixteen
(3.6%) were “electric detonators,” while a further thirty-three were “miss detonators” (Fehlzündungen).

Obviously this is a rather complicatedsystem of classification, and it is not necessary for the purposes of this study to knowthe exact meaning of each of these vague subcategories. What is pertinent to this study is that tallying up all the individual sub-categories together reveals a total of 101 torpedoes for 23 percent of the total torpedoes fired that spontaneously exploded without hitting either the target or another object. Any of these explosions could have been noticed by an accompanying escort vessel, alerting it to the U-boat’s location and hence jeopardizing the safety of the U-boat and its crew.

Short version:

Data about Torpedoes equipped with the Pi A+B pistol - MZ setting.
period: November 1939 to June 12, 1940
fired: 440 with magnetic setting (out of 531 total eels fired).
premature detonations: 101 (23%).

So, consider how do you would feel, as a kaleun, if every 4th eel you attempt to fire is not a weapon that you throw at your enemy but an out loud scream to every ear in your sorrounding that say: "HELLO WORLD!!!".
And here we are only counting the fishes that went Ka-boom too early, add in also the dud ones and the wrong-depth runners and I let you imagine how much the failure rate climbs...

(Btw, after June 12, 1940, Bdu ordered to fire torps with the AZ setting, and due to the recents improvements on the pistol the failure rate dropped significantly, coincidentally this time frame mark the start of the "Happy Time" and MZ detonation would not be used again until 1942).