Actually the torpedoing of the Wilhelm Gustloff led to the death of over 9000.
But that wasn’t a “British Maritime Loss” was it?
Correct. Soviet sub sank the Wilhelm Gustloff—as many as 9,400 people were killed on 1/30/45:
https://en.wikipedia.org/wiki/MV_Wilhelm_Gustloff
Largest loss of life in the sinking of a ship in history.
I was just about to bring that up. I’m thinking too that that was the only Soviet action by one of their subs in the whole of WW2 - I could be mistaken (maybe).