Dora 1 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 . History . Background . 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 . 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 thick and reinforced with steel . The walls were also concrete but these were thick . The whole bunker was . 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 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 - boat s . 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 Force s ; 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 .