Hello GoldenRivet,
yeah, already cooled down. You are certainly right, but it IS just so frustrating

.
Imagine running even as fast at 5 knots submerged - there is no way anyone would have heard you in a 600 m radius of a lumbering merchant in mid-convoy - well, in reality, that is.
Escorts were faar away. And there was no sonar for sure.
Only a question, i did exercise some surface attacks at night before, but i would never come as near as to 600 m without being seen. Indeed they would spot me at some 4000 meters in pitch-black night in 1939 - so it seems it is not possible to make a typical early years-surface attack ?
Oh well, i wrote i like the challenge, seems i have to live up to that.
Greetings,
Catfish