I haven't seen or sunk a Queen Mary Liner. Got a torpedo into the Hood once but she shrugged it off and sailed on.
Once I, almost, sank two battleships in one patrol:
I hit the Revenge, moving in the middle of a convoy at 5 knots, with 3 torps and she went down like a rock:
Then towards the end of my patrol (4 torpedoes left) I came across the Rodney under similar conditions (middle of the convoy moving 8 knots):
She went dead in the water, started to settle be the bows and then just floated there. I waited until the rest of the convoy sailed on, rose to periscope depth and waited some more. And waited, and waited. I finally took a stern shot at her with my last torpedo. The torp premed about 100 meters short. I waited around for two days but she just laid there. I was so frustrated that thought of ramming her went through my mind (very briefly).
Finally I sailed home.