The submarine pens built in WWII were some of the biggest concrete construction works of the war, and some of toughest targets throughout all of Europe. These immense structures were built to to protect Germany’s submarine fleet from aerial attack while refuelling, refitting or repairing.
The idea of protecting submarines from attack was first explored in WWI with wooden shelters, a time when men were dropping bombs weighing a fell kilograms from aircraft by hand. By WWII, aircraft were now carrying bombs weighing in the tons, and as such the levels of protection for the U-boats needed to be increased dramatically.
Britain’s refusal to surrender, plus the RAF attack on Berlin in 1940 meant commanders were convicted of the need to protect their submarine fleet.
The Saint-Nazaire submarine base. Image credit – Rama CC BY-SA 2.0
Construction of submarine bunkers in Hamburg and Heligoland island began, with many more on the way. The enormous scale of these bunkers made it clear from early on this was above the abilities of the Navy, so the civil and military engineering establishment Organisation Todt was brought in to take over the work.
Organisation Todt undertook the Third Reich’s biggest engineering projects, including the Autobahn network in its early days, the Atlantic Wall, many factories, air raid shelters and defensive networks in Germany.
In areas where the population was less resistant to their occupiers, much of the labour was performed by local workers. In places where the Nazi’s were less accepted, recruiting locals wasn’t an option, so forced labour was brought in from concentration camps near the construction site. Essentially slaves, these workers were subject to extreme inhumane treatment, with little food or water and often worked until they died.
Aside from their vast size, submarine bunkers were complex in their design. They had to provide office spaces, medical facilities, accommodation for personnel, storage for submarine supplies and spares, ammunition, anti-aircraft defences, fuel and power generators.
Allied air raids often harassed the worksites, damaging equipment and materials, disruption construction. Unfortunately, local civilian areas around the pens were also subject to bombs in collateral damage, and many of the slave labourers died during these attacks.
The bunkers were designed to be immune to all Allied bombs, with some having roofs up to 8 m thick (26 ft). These were enough to resist Allied bombs, accept two; the Tallboy and Grand Slam bombs. These British bombs weighed 12,000 lbs and 22,000 lbs respectively.
The 22,000 lb Grand Slam bomb.
They would reach supersonic speeds as they fell, burrowing into a target or the ground before exploding, with a thickened steel casing. The bombs were even able to destroy targets with a miss, as the shockwave travelling through the ground would subject the target to a localised earth quake, destroying it at its foundations.
While conventional bombs simply tickled the submarine pen roofs, a direct hit from a Tallboy or Grand Slam would do serious damage.
A new harbor basin is being excavated in front of the submarine boxes. Small tilting lorries move the earth away.
A view of the ruins of the U-Boat pens at Hamburg after their demolition.
An RAF officer inspects the hole left by a 22,000-lb deep-penetration ‘Grand Slam’ bomb which pierced the reinforced concrete roof of the German submarine pens at Farge, north of Bremen, Germany.
Bomb craters on the roof of a building at the German submarine base, Brest, France.
Brest U-boat pens after liberation, 1944
Brest U-boat pens after liberation.
Concrete shelters for German submarines on the Atlantic coast.
Concrete U-boat pens at Hamburg.
Working from rafts on the water, sappers of the Royal Engineers cut through steel girders of the Hamburg U-Boat pens to make spaces to house the explosive charges needed to demolish the pens.
In preparation for the demolition of the U-Boat pens at Hamburg, sappers of 224 Field Company, Royal Engineers, lower a German 250 kilo bomb into a well hole in the floor of the pens.
In preparation for the demolition of the U-Boat pens at Hamburg, Sapper Stidson from the Royal Engineers connects a group of German bombs with Cordtex-instantaneous detonation fuse.
In preparation for the demolition of the U-Boat pens at Hamburg sappers of 224 Field Company, Royal Engineers, roll out the firing cable once all the explosive charges are in place.
The U-Boat pens at Hamburg going up in smoke.
Construction of the Bremen U-boat pens. Bundesarchiv CC BY-SA 3.0
France, Lorient, submarine bunker under construction. Bundesarchiv CC BY-SA 3.0
German submarine base, Brest, oblique aerial view, on the right is the Naval Academy.
German U-boat pen ‘Valentin’ under construction. Bundesarchiv CC-BY-SA 3.0.
German U-Boat pens at Hamburg with a scuttled U-Boat in the foreground.
In preparation to demolish the U-Boat pens at Kiel an old cargo-ship is moored across the entrance to the pens to stop the blast damaging private property across the river.
Inside the Brest submarine pen on the Atlantic. Here, the submarines that have returned from a long patrol are repaired and re-equipped as necessary. Bundesarchiv CC BY-SA 3.0
Interior of the E-boat pens at le Havre, showing the collapsed roof, caused by 12,000-lb deep-penetration ‘Tallboy’ bombs dropped by No. 617 Squadron RAF on 14 June 1944.
Japanese submarine I-8 in Brest.
Original Caption – The giant bunkers on the Atlantic In a huge symphony of work, the giant bunkers were built on the Atlantic coast, providing our submarines with bomb-proof bases. October 1942
Prefabricated U-boat sections at Hamburg.
Remains of the U-Boat pens at Kiel after the explosion of the demolition charges.
Submarine bunker ‘Valentin’ under construction, Bremen. Bundesarchiv CC-BY-SA 3.0
The explosion caused by the detonation of charges to demolish the U-Boat pens at Kiel.
U-boat pens in St. Naziere. Bundesarchiv CC BY-SA 3.0
15-foot reinforced ferro-concrete U-Boat pen roof penetrated by a 22,000 lb MC Grand Slam bomb
A British soldier from 224 Field Company, Royal Engineers, examines a hole made by a 12,000 lb bomb in the 11 foot thick concrete roof of the German submarine pens pens at Hamburg.
A column of forced laborers walking next to wooden scaffolding of the Bremen U-boat pens. Bundesarchiv CC BY-SA 3.0
