In 1941, construction of the DORA 1 submarine base started in Trondheim. Two years later, in June 1943, it was handed over to the flotilla commander, Korvettenkapitän (later Fregattenkapitän) Rolf Rüggeberg. The 13th submarine flotilla was a front line unit, and a total of 55 Type VIIC and VIIC/41 served with it until the end of the war in May 1945.