Like her sisters, "Karlsruhe" served as a training cruiser for naval cadets throughout the 1930s. During the Spanish Civil War, she joined the non-intervention patrols off the Spanish coast. She was in the process of being modernized at the outbreak of World War II in September 1939, and was therefore not ready for action until November 1939. In April 1940 "Karlsruhe" participated in Operation Weserübung, the invasion of Norway. She landed troops at Kristiansand, but while returning to Germany on 9 April, she was struck by a torpedo from the Royal Navy submarine and severely damaged. Unable to return to port, "Karlsruhe" was scuttled by an escorting German torpedo boat.