Thanks guys, makes sense. What actually happened to prompt me writing this was i was about 8000m from a large cargo. I then noticed two small river class warships approaching me. I was not sure initially if they saw me however when I realised, I launched all 4 bow torpedoes towards two ships including the large cargo. I then crash dived to 115m and the river class did bugger all really and i got away. So this poses two questions, how do I know if the warships saw me or their radar detected me ( I did not get radar signals detected at that time, although I did when I surfaced for the attack chasing the convoy ) and unfortunately all but one of my torpedoes prematurely detonated, the waters were quite choppy, do you think this was the cause or just bad luck. My other torpedo missed.
Thanks