Im sorry, but if a uboat captain or any other sub captain could have the opportunity to sink another sub i would have thought he would take it, considering the amount of damage they can inflict on there convoys/warships, so to say leave them alone doesn't really add up to me.
In this game the obj/missions/patrols are flawed as has been mentioned in other posts.
I will sink anything i can as long as it does not jeopardise whatever the mission i am on, not that there are any mission/patrols it can ruin.
Nico