|Trondheim, in central Norway, was one of the most important portal cities in Norway during the war. Today she is the 3rd largest city in Norway. From there the 13th Flotilla operated from June 1940 until its surrender in May 1945 sending its 55 U-boats out to combat the Allies.|
The bunker was constructed since it was needed more repair facilities outside of Germany and the facility had to be well protected. The bunker at Trondheim, while under construction, came under the jurisdiction of the Todt organization.
Work on Dora 1 started in in the spring of 1941. It was handed over to the Kriegsmarine on 20 June 1943. The second bunker, Dora 2, was started in 1942. This bunker was never completed. The second bunker was a little more than half complete by the time the war ended.