My tactic is to directly in front of the convoy at a 30 degree angle facing toward them. I then go silent running and drop down to about 20 feet and shut off the engine. I then get on the hydrophone and listen. When I hear the first ships start to pass over me, I creep up to periscope depth at three knots silent running and fire everything I have at everything that's moving. This is followed by a crash dive and a silent run of 2 or 3 knots accross the direction of travel of the convoy so i emerge out the other side and get away nice and safe. So far this tactic has worked well for me (knocks wood).
