text: german u - boat bases in occupied norway german u - boat bases in occupied norway operated between 1940 and 1945 , when the kriegsmarine ( german navy ) , converted several naval bases in norway into submarine bases . norwegian coastal cities became available to the kriegsmarine after the invasion of denmark and norway in april 1940 . following the conclusion of the norwegian campaign ( june 1940 ) , the occupying germans began to transfer u - boats stationed in germany to many norwegian port cities such as bergen , narvik , trondheim , hammerfest and kirkenes . initial planning for many u - boat bunkers began in late 1940 . starting in 1941 , the todt organisation began the construction of bunkers in bergen and trondheim . these bunkers were completed by & ag between 1942 and 1943 . the kriegsmarine generally used u - boats stationed in norway to extend its range of operation in the north atlantic and arctic oceans . the norwegian bases housed u - boats that took part in the interception of allied convoys crossing the arctic ocean to the soviet union . following the liberation of france by the western allies in 1944 , u - boat activity in many norwegian ports increased . with the french ports captured or cut off , many german u - boats re - located to norwegian port cities . during the german occupation of norway , the kriegsmarine stationed over 240 u - boats in the nordic country at one time or another , most of them members of the 11th u - boat flotilla , which had 190 u - boats in its fleet during the flotilla 's entire career . other well - known flotillas in norway included the 13th and 14th flotillas . german invasion of norway germany invaded both norway and denmark on 9 april 1940 . norway was very important to germany for two reasons : firstly as a base for naval units to harass allied shipping in the north atlantic and arctic oceans , and secondly to secure shipments of iron ore coming in from sweden through the port of narvik . during operation weserübung , denmark fell in less than a day , becoming the briefest invasion in recorded military history . the norwegians put up a stiffer resistance to the invading german forces . nonetheless , by may the southern half of norway was under german control . following the german invasion of france and the low countries , the allies were forced to evacuate narvik , leaving the country to the germans who would occupy it until the end of the war . after the invasion , vidkun quisling led the collaborationist government of norway , based around the fascist nasjonal samling ( " national gathering " ) party . german use of norwegian ports during the occupation , several of the nation 's naval ports were turned into u - boat bases that were used to harass allied shipping in the north atlantic and arctic oceans . these included bergen , narvik , trondheim , hammerfest and kirkenes . over 240 u - boats were stationed in norway at various times during the war , most of them were members of the 11th u - boat flotilla which had 190 u - boats in its fleet during the flotilla 's career . other well - known flotillas in norway included the 13th and 14th flotillas . bergen the southern port of bergen was captured by the germans on 9 april 1940 , on the first day of the invasion . the germans immediately saw the potential for several norwegian harbours and ports to function as bases of operation for the kriegsmarine 's u - boats patrolling the north sea and the arctic ocean . it would become the home of the 11th u - boat flotilla . bergen was the first norwegian port to be established as a u - boat base . from july 1940 to the end of the war in may 1945 , 270 u - boat patrols originated in bergen . bergen was also the site where the only type xxi submarine left for a patrol in the war ; u - 2511 left the port on 3 may 1945 . planning for the first u - boat bunker in bergen began in late 1940 and was undertaken by the german military engineering group , the todt organisation . it coordinated the building of the first u - boat bunker in bergen , codenamed bruno , as well as several other u - boat bunkers along the norwegian coast . the construction of bruno began in 1941 . when it was completed it had seven pens , three of which were " dry " docks and three of which were " wet " docks . the seventh pen was used for storing fuel , torpedoes and other essentials . the bunker itself had a roof up to 6 metres ( 20 ft ) thick and was 131 metres ( 430 ft ) by 143 metres ( 469 ft ) in area . once bruno was completed , it could hold up to 9 u - boats . bergen remained a quiet base during the first few years of the occupation , experiencing only one large allied air attack . in 1943 , the u - boat base added two new bunkers , u - stützpunkt prien and u - stützpunkt along with a shipyard named danziger werft . the u - boat base at bergen grew exponentially after the liberation of france by the western allies , when the senior commanding officer of u - boat operations in the west ( " west " ) was moved from angers , france to the city . a large expansion program was conducted at the base and several new anti - aircraft guns were set up to protect the u - boat bunkers . more engineers and technicians were moved to bergen to accommodate the increased technical requirements of the base as well . two more bunkers named werft 1 and 2 were also built during this time . in late 1944 several british air attacks damaged the u - boat bases in bergen . during one of these attacks , a ' tallboy ' bomb went straight through the roof of pen 3 , damaging it beyond repair and putting it out of action for the remainder of the war . the base was handed over to the allies , along with the rest of occupied norway , on 8 may 1945 when all german forces in europe surrendered . as a result of the intensive bombing of the city in late 1944 and 1945 , the bergen area was one of the worst damaged regions in the south of norway at the conclusion of the war . trondheim trondheim was an important u - boat base in norway during the war . it was the home of the 13th flotilla and sent out around 55 u - boat patrols between june 1940 and the end of the war in may 1945 . the list of u - boats in trondheim included following : u - 310 , u - 315 , u - 483 , u - 773 , u - 775 , u - 861 , u - 953 , u - 978 , u - 994 , u - 995 , u - 1019 , u - 1064 and u - 1203 . two u - boat bunkers , codenamed " dora i " and " dora ii " , were planned to be built in trondheim to provide additional repair facilities outside germany itself . like the bunkers in bergen , the two bunkers in trondheim came under the control of the todt organisation . only " dora i " , which the kriegsmarine took charge of in 1943 , was completed before the end of the war . at 153 feet ( 47 m ) long and 105 feet ( 32 m ) wide it had five pens with space to hold seven u - boats . construction of " dora ii " began in 1942 but was never completed . if finished it would have been 168 feet ( 51 m ) long by 102 feet ( 31 m ) wide , with four pens capable of holding six u - boats .