Dora 1 is a former German submarine base and bunker built during World War II in Trondheim, Norway. Trondheim was traditionally referred to as Drontheim in German, and the name DORA is the letter "D" in the German phonetic alphabet.
Following the occupation of Norway in 1940, it was soon realised that the country only had limited facilities for minor naval repairs. More extensive work usually meant a return to Germany. The capitulation of France two months later overshadowed the strategic importance of Norway to some extent, but it was still regarded as a better location for access to the Atlantic and Arctic Oceans than Germany. Nevertheless, better protection for U-boats from aerial attack was required so a bunker-building programme was instigated.
Construction of the bunker which would become part of the largest German naval base in Northern Europe, started in the autumn of 1941, one year after the invasion of Norway. The concrete roof was 3.5 m (11 ft 6 in) thick and reinforced with steel. The walls were also concrete but these were 3 m (9 ft 10 in) thick. The whole bunker was 153 m × 105 m (167 yd × 115 yd). The work was undertaken by the Todt Organisation's (OT) Einsatzgruppe 'Wiking' and the Sager & Wörner construction company from Munich.
The OT used slave labour extensively; five Serbian workers died when a wall fell on them. This incident fuelled a widespread urban legend that the Germans simply left the bodies inside the wall. While German engineers did calculate that the five bodies would not weaken the fortification considerably, the bodies were removed before construction continued.
Difficulties with the labour force was not the only problem. The acquisition of raw materials was also a problem. Many Norwegian buildings were erected from timber so cement, sand and aggregate - components essential for the production of concrete - were often hard to extract in sufficient quantities. The steel required for reinforcing was mostly imported from Germany. The weather also played its part; roads and railways were often affected by snow and ice. Pre-fabricated accommodation units from Germany proved to be inadequate. More ships were delayed by the weather than enemy interference. Most construction machinery also had to be imported.
The bunkers in Norway were originally slated for a second floor to be built over the submarine pens. This was to house accommodation, workshops and offices. The idea was abandoned at the end of 1941 due to the problems already mentioned. The choice of site did not help either. Accumulated mud, on top of clay and sand layers proved to be incompatible with existing designs.
Dora 1 developed a noticeable sag of up to 15 cm (5.9 in) which seemed to concern the builders more than the U-boat men. It was finally handed over to the Kriegsmarine on 20 June 1943 as the home base of the 13th U-boat Flotilla. The bunker, which could be hermetically sealed when attacked, had room for 16 U-boats.
Construction of a smaller bunker to the west of Dora 1, Dora 2, was started in 1942, but it was only half-completed by the end of the war. This building is presently used by a shipyard.
After World War II
After the war, Dora 1 was to be blown up using dynamite, but this project was eventually cancelled due to the massive construction and the sheer size of the bunker. Blowing it up would have caused serious damage to the surrounding buildings as well. The base was used briefly by the Norwegian Defence Forces; two extra stories, painted in blue, were added.
Today, the former naval base is the home of the city and state archives, a bowling alley and several other businesses. The submarine pens originally built for holding German U-boats are now being used as a harbour for civilian boats.