Immediately upon entering service, "Blücher" was assigned to the task force that supported the invasion of Norway in April 1940. "Blücher" served as the flagship of "Konteradmiral" (Rear Admiral) Oskar Kummetz, the commander of Group 5. The ship led the flotilla of warships into the Oslofjord on the night of 8 April, to seize Oslo, the capital of Norway. Two old coastal guns in the Oscarsborg Fortress engaged the ship at very close range, scoring two hits, as did several smaller guns in other batteries. Two torpedoes fired by a torpedo battery in the fortress struck the ship, causing serious damage. A major fire broke out aboard "Blücher", which could not be contained. The fire spread to one of her anti-aircraft gun magazines, causing a large explosion, and then spread further to the ship's fuel bunkers. "Blücher" then capsized and sank with major loss of life.