Production of U-boats by German shipyards had been dramatically reduced by bombing by the Royal Air Force and the United States Army Air Forces. So many bomb-proof production sites were 1944 already in use as for example the U-boat pen Nordsee III on the German island Heligoland, Fink II and Elbe II in Hamburg and Kilian in Kiel, under construction or planned as Hornisse in Bremen, Elbe XVII and Wenzel in Hamburg, Wespe in Wilhelmshaven, Kaspar in Kiel and some more in Germany and in occupied countries. Under the codename Valentin a submarine factory was to be built directly at the Weser river between the Bremen suburbs Rekum and Farge. It was intended the facility would be used for the final assembly of Type XXI submarines, starting in April 1945 with 3 boats and from August 1945 a monthly delivery of minimal 14 boats. Besides this a further bunker called Valentin II was already planned.
The bunker is around 426 metres (1,398 ft) long and 97 metres (318 ft) wide at the widest point; the walls are 4.5 metres (15 ft) thick. The height of the structure is between 22.5 and 27 metres (74 and 89 ft). The roof was constructed using dozens of large, reinforced concrete arches, manufactured on-site and individually lifted into place. Most of the roof is around 4.5 metres (15 ft) thick but part of it is 7 metres (23 ft) thick as the Germans began adding to its thickness before the bunker was even completed. Construction required 650,000 cubic yards (500,000 m3) of concrete.
After completion, the bunker would have had a work–force of around 4,500 slave workers. Under the management of the Bremer Vulkan shipyard, each U-boat would have been assembled from eight, large, pre-fabricated sections manufactured in other shipyards such as Bremer Vulkan, Deschimag AG Weser with its bunker Hornisse, Kriegsmarinewerft Wilhelmshaven ´with bunker Wespe and Deschimag Seebeckwerft in Bremerhaven, and then shipped to Valentin on barges.
The bunker was to house 13 assembly bays (in German called Takt 1-13), each carrying out one part of the assembly process. Two bays (Takt 9/10) were underneath box-like structures on the roof that allowed the extra height needed for the installation of periscopes, submarine snorkels and antennas. The two last bays (Takt 12/13) were separated by high walls from the others and could be closed by water-tight floodgates. The final bay (Takt 13) was a dry dock with an 8 metres (26 ft) deep pool of water. The two separated bays could be flooded to altogether about 20 metres height from the bottom of the dock to the water-surface. When the floodgates were closed the boats would be launched from Takt 12 to Takt 13 and leak–tests of the completed U-boats as well as engine starts and several other tests were carried out in the dock Takt 13. Besides these assembly bays, there were several workshops and store-rooms for the prefabricated sections, diesel-engines and batteries, and tanks for fuel and lubricants.
The gateway in the western wall could be closed by a sliding bomb-proof door which opened to a small canal, a creek and then directly onto the Weser river. Through this, sections of submarine would be delivered by barges and completed submarines would leave.
It was intended that Valentin would commence production in late 1944, but this was postponed to mid-1945. However, if Valentin had been commissioned it is likely production would have been limited unless severe quality control problems with the prefabricated sections could have been solved (Albert Speer had directed the sections should be made by inland companies with little experience in shipbuilding). The Type XXI submarines assembled in other shipyards required lengthy re-working to fix flaws in the sections; out of the 118 boats completed, only four were rated fit for combat before the war ended in Europe.
The design and oversight of the Valentin's construction was carried out by Organisation Todt. Marineoberbaurat Edo Meiners was in charge overall; the on-site supervising engineer was Erich Lackner. He had a lengthy post-war career, becoming one of Germany's most important civil engineers.
Most of the 10,000-12,000 who built Valentin were slave workers, who lived in seven camps located between 3 and 8 kilometres (1.9 and 5.0 mi) from the bunker. Some were housed in the nearby Bremen-Farge concentration camp, a satellite camp of the Neuengamme concentration camp complex. The camp was sited at a large naval fuel oil storage facility; some prisoners were accommodated in an empty underground fuel tank.
The camp was initially run by the SS, but the expansion of the camp network in the area led to a shortage of personnel. By the summer of 1944, the camp was commanded by an army captain, Ulrich Wahl, and the prisoners were guarded by a detachment of naval infantry. Only a handful of SS men remained involved in the running of the camp.
The prisoners included German criminals and political prisoners, non–German civilian workers (Fremdarbeiter) as well as Russian, Polish, French and Greek prisoners of war.
Work on the bunker took place around the clock, with workers forced to work 12-hour shifts from 7am to 7pm. This resulted in a high death rate amongst prisoners. However, the identity of only 553 victims, mostly French prisoners, has been confirmed. The total number of deaths may be as high as 6,000 as the names of the Polish and Russian dead were not recorded. The worst work on the site was that of the so-called iron detachments (Eisenkommandos), responsible for the movement of iron and steel girders. A French survivor, Raymond Portefaix, stated that a prisoner's life expectancy fell dramatically on being assigned to one of these detachments. He described the Eisenkommandos as suicide squads.
By March 1945, the facility was 90% completed and the most of the necessary machine tools had been installed. Production of U-boats was due to begin within two months.
Read more about this topic: Valentin Submarine Pens
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