I am not sure about the SS1 failure rate but on the SS3 a fleetmate did a test. To
keep things short we counted the failures out of 100 torps of each SS3 from each
nation.

We came to the conclusion that the failure rates where:

33% for UK, US and IJN
27% for KM

So you have a general idea of the failure rates. Tho Tier 1 uses different torps so it
might be completely different from the SS3.

I think its just random

i think it doesnt really matters.
all you need to do is to know the range of your torps.
and by some approximations, release your torps when the target is somewhere
near your max range, even if it doesnt explode on contact, the splash damage will
do the job.
I realise that the speed affects the hit rate too.
If u are real close, try using slow and aim ahead, instead of using fast.
My logic is that, you are at certain depth under water, if you use fast, the torp wont
raise to the so called hit depth, so most likely will pass under the targer..
but when you use slow speed, the torp will raise up to the hit depth b4 reaching the
target.
not really sure whether this is true or not.

Thank you for your re'ly. It was most helpful. I think the slapsh damage is the biggest
part of the IJN torps.

i have tested the HitRates on Subs, but only on T3 ones (specially because im considering
every tier having same Dud rate)

so basicly.... every nation gave me a 70% HitRate, expect KM which, with some analogies,
they have exacly 91% HitRate

but i have to say, when i was testing the IJN, there were 2 to 3 moments where they missed
both 4 shooted torps, whilst other nations this never happened! But in the end Hit Rate
gave me 69,4%, which i believe the right number might be 70%!

It probably wouldn't be too hard to test at fixed sailor skill (I suspect that the dud
rate is unrelated, though)

*ponders*

No clue, SDE has not released the ratios, and whatnot.

what I do know, is IJN has the highest dud rate.