Unless I'm mistaken, the Japanese only had one "huge European Liner", the Conte Verde. She was a cruise ship that that got scuttled to prevent the japanese from using it, but they were able to raise the ship and turn it into a troop carrier.
Early on in my SH4 career, I found the big huge european liner, heading south, under destroyer escort and managed to sink it.
I was very pleased with myself. I thought "wow, I found this one of a kind ship and sunk it". But two patrols later I found two more "huge european liners", and then a third, each part of different convoy groups. A degree of frustration kicked in, just because I felt like, to the best of my knowledge, the japs shouldn't have anymore of these. (I acknowledge I could be wrong, my research on this only extends as far as a brief google search)
They've become my "white whale" so to speak. Big tonnage score aside, when I see one, a big bullseye appears in my mind and I always make an attempt to get it. Only one has ever escaped me, because of dud torpedoes and a fierce destroyer that spotted me early in my attack and forced me to dive and escape the area.