This almost always works for me. Be at periscope depth, & Make sure you have a stern tube ready to go, set to depth of 2m, fast speed, door open. Turn towards the attacker, at standard speed and when he gets to around 700m and closing, do a sharp turn to the left, maybe 60 degrees off your initial course, & increase to flank.
The attacker should pass off your stern, and when he is close (less than 200m)IMMEDIATELY turn 90 to 120 degrees to the right. He should pass close and drop charges and if you are lucky your stern will swing around far enough that it does no damage. Immediately bring up your scope and look to the rear. Your attacker should have passed you and now most likely be turning to the right so that he is broadside to your stern tubes at about 400m. I lock him up and send one at him usually breaking him in half.. I do this all the time and have sank all 4 escorts in convoys in late 41 before i even bother with the convoy using this method.
Try it
Tool.