"Schlesien" saw limited combat during World War II, briefly bombarding Polish forces during the invasion of Poland in September 1939. She escorted minesweepers during Operation Weserübung, the invasion of Norway and Denmark in April 1940. After the operation, she was given secondary duties, primarily serving as a training ship and icebreaker. She ended her career providing fire support in the Baltic coast. While off Swinemünde on 3 May 1945, she struck a mine and was towed into Swinemünde, where she was sunk by her crew in shallow water, though much of her superstructure, including her main battery, remained above water. In the remaining days of the war, "Schlesien" used her anti-aircraft guns to defend the city from air attack. After the end of the war, she was broken up, though some parts of the ship remained visible until the 1970s.