Overview of Overview of GERMANGERMANUU--BOAT BASES AND BOAT BASES AND BUNKERSBUNKERS1941 1941 --19451945J. David RogersJ. David RogersBACKGROUND 1BACKGROUND 1German UGerman U--Boat fleet under the command Boat fleet under the command of of KonteradmiralKonteradmiralKarl Karl DonitzDonitz..As World War II erupts in September As World War II erupts in September 1939, the U1939, the U--Boat shows it’s potential:Boat shows it’s potential:Penetrated Royal Navy Home Fleet Penetrated Royal Navy Home Fleet anchorage at anchorage at ScapaScapaFlow, Scotland Flow, Scotland Sank the battleship Sank the battleship HMSHMSRoyal OakRoyal OakEscaped with easeEscaped with easeShots firedLocation of the Royal OakUnderwater obstaclesBACKGROUND BACKGROUND --22Late spring and summer of 1940, the German Late spring and summer of 1940, the German juggernaut invaded Norway, France and the juggernaut invaded Norway, France and the Low Countries, overwhelming all of them in a Low Countries, overwhelming all of them in a matter of weeks.matter of weeks.Germany took control of the port facilities Germany took control of the port facilities available to them.available to them.Prior to this acquisition, the distance to Prior to this acquisition, the distance to open sea from German ports in the Baltic open sea from German ports in the Baltic limited their range while also increasing limited their range while also increasing wear and vulnerability.wear and vulnerability.The down side was that all the new ports The down side was that all the new ports were within easy striking distance of were within easy striking distance of British bombersBritish bombers..• 1170 Patrols made from these 3 locationsBACKGROUND BACKGROUND --33Prior to war, UPrior to war, U--Boats were usually serviced Boats were usually serviced alongside their designated flotilla tender.alongside their designated flotilla tender.UU--Boats are more vulnerable to damage than Boats are more vulnerable to damage than surface vessels:surface vessels:If their pressure hull integrity is If their pressure hull integrity is compromised, a Ucompromised, a U--Boat would be unable to Boat would be unable to dive.dive.Most UMost U--Boats were not fit with adequate Boats were not fit with adequate firepower to protect themselves on the firepower to protect themselves on the ocean surface.ocean surface.Biggest vulnerability was detection and Biggest vulnerability was detection and attack by enemy aircraftattack by enemy aircraftLimited AntiLimited Anti--Aircraft firepowerAircraft firepowerU-Boats were initially fitted with a single 20 mm AA gun; later increasing to two (shown at left) and then four barrel configuration, shown belowSome specially-fitted U-flak boats were equipped with quad mount 2.2 cm anti-aircraft guns to provide additional AA protection for Wolf Packs.Concrete Pens Constructed to Concrete Pens Constructed to Protect the UProtect the U--Boats in coastal portsBoats in coastal portsThe German’s preThe German’s pre--war labor force war labor force consisted of approximately 300,000 consisted of approximately 300,000 laborers.laborers.After the outbreak of WW2, POWs and After the outbreak of WW2, POWs and concentration camp inmates were put to concentration camp inmates were put to work.work.Approximately 15,000 laborers were Approximately 15,000 laborers were needed to construct a massive Uneeded to construct a massive U--Boat Boat bunker.bunker.Construction of UConstruction of U--Boat PensBoat PensConstruction proceeded 24 hours a day Construction proceeded 24 hours a day using two 12 hour shiftsusing two 12 hour shiftsLights were used to facilitate work Lights were used to facilitate work throughout the night (except when under throughout the night (except when under attack)attack)Hazardous working conditionsHazardous working conditionsConstruction OperationsConstruction OperationsMaterials were initially transported from Materials were initially transported from GermanyGermanyCement in 50kg sacksCement in 50kg sacksReinforcing SteelReinforcing SteelMaterial requirements were vast, they Material requirements were vast, they were sourced locally and transported:were sourced locally and transported:RailroadRailroadBargesBargesTrucksTrucksBUNKER DESIGNBUNKER DESIGNWet and Dry Wet and Dry Docks in covered Docks in covered bombbomb--proof baysproof baysLock gatesLock gatesOfficesOfficesStorage facilitiesStorage facilitiesMachine ShopsMachine ShopsGeneratorsGeneratorsBUNKER DESIGNBUNKER DESIGNEach pen was designed as a free-standing drydock so essential maintenance and battle damage repairs could be carried out between combat deploymentsPRODUCTION BUNKER LAYOUTPRODUCTION BUNKER LAYOUTThe The Germans Germans also also enclosed enclosed all their Uall their U--Boat Boat production production facilities to facilities to resist resist Allied Allied bombingbombingCOASTAL BUNKER DESIGNCOASTAL BUNKER DESIGN• Biggest design concern was overhead protection from Allied bombing• Initial construction was bomb proof; but the bombs got bigger as war dragged onPROTECTION UPGRADESPROTECTION UPGRADES• Re concrete roof reinforced thickness up to 7 meters• Fangrost screens constructed on roofsThe RAF developed 12,000 lb Tallboy and 22,000 Grand Slam bombs to interdict U-Boat pensDEFENSIVE STRATEGYDEFENSIVE STRATEGYIncoming raid Incoming raid detected by radardetected by radarScramble fightersScramble fightersIntercept with AA Intercept with AA fire located in fire located in cities/portscities/portsRely on strength of Rely on strength of bunkerbunkerto resist to resist bomb penetrationbomb penetrationDEFENSIVE OPERATIONSDEFENSIVE OPERATIONSAs war As war progressed, progressed, biggest fear biggest fear was low flying was low flying fightersfightersTorpedo or Torpedo or bomb lobbomb lobBarrage Barrage balloons, balloons, torpedo net, torpedo net, AA positions, AA positions, steel doorssteel doorsBOMB DAMAGE ASSESSMENTBOMB DAMAGE ASSESSMENTThis aerial image shows craters caused by Allied air attacks before emplacement of fangrost covers to absorb bomb detonations.PRESENT DAY USEPRESENT DAY USEAfter the war it proved impractical to scrap After the war it proved impractical to scrap the Uthe