MV Wilhelm Gustloff was a German military transport ship which was sunk on 30 January 1945 by Soviet submarine S-13 in the Baltic Sea while evacuating civilians and military personnel from East Prussia and the German-occupied Baltic states, and German military personnel from Gotenhafen (Gdynia) as the Red Army advanced. By one estimate, 9,400 people died, making it the largest loss of life in a single ship sinking in history.

S-13 was a Stalinets-class submarine of the Soviet Navy. Her keel was laid down by Krasnoye Sormovo in Gorky on 19 October 1938. She was launched on 25 April 1939 and commissioned on 31 July 1941 in the Baltic Fleet, under the command of Captain Pyotr Malanchenko. The submarine is best known for the 1945 sinking of Wilhelm Gustloff, a German military transport ship/converted cruise ship. With a career total of 44,701 GRT sunk or damaged, she is the highest-scoring Soviet submarine in history.