I've had good success with keel shots even early in the war, as long as the torpedo travels diagonally. If I shoot from ahead, the torpedo will explode toward the aft section of the shipcausing damage to engine room and rudder (I believe) with catastrophic effect.
Perpendicular shots, often will explode on the opposite side of target without causing serious damage. I set magnetic shots to run 1.5 meters below the ship's keel.
Hope this helps
