Tactical flaw in the early story
I realize it was to set up the subsequent story line on the sub, but the handling of the Q-ship was so wrong. By 1943, sub commanders were a pretty savvy bunch. Presenting your beam to an unknown ship would be a recipe for disaster. The sub should have been positioned with its stern toward the unknown ship. The deck gun could still be employed, while also making the stern torpedo tubes available for attack, plus presenting a much smaller target to the Q-ship and being in a position to depart at high speed while still firing the deck gun and stern tubes.