page_title: Valentin submarine pens
section_title: Construction
hierarchical_section_title: Valentin submarine pens / Construction
context_page_description: The Valentin submarine factory is a protective shelter on the Weser River at the Bremen suburb of Rekum, built to construct German U-boats during World War II. The factory was under construction from 1943 to March 1945 using forced labour, but was damaged by air-raids and unfinished by the end of the war. The Valentin factory was the largest fortified U-boat facility in Germany, and was second only to those built at Brest in France.
  As a manufacturing facility, it differed from conventional U-boat pens, which were designed to house and service operational U-boats.
context_section_description: Production of U-boats by German shipyards had been dramatically reduced as a result of bombing by the Royal Air Force and the United States Army Air Forces, necessitating the creation of bomb-proof production sites. Many such sites were in use in 1944, including the U-boat pen Nordsee III on the German island of Helgoland, Fink II and Elbe II in Hamburg and Kilian in Kiel. Other sites in Germany and other occupied countries were under construction or planned, such as Hornisse in Bremen, Elbe XVII and Wenzel in Hamburg, Wespe in Wilhelmshaven, Kaspar in Kiel. Under the codename Valentin a submarine factory was to be built directly on 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 three boats and from August 1945 a monthly delivery of a minimum of 14 boats. A second bunker called Valentin II was planned as well.
  The bunker is around 426 metres (1,398 ft) long and 97 metres (318 ft) wide at its 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.
  The design and oversight of the Valentin's construction was carried out by the 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 prominent civil engineers.
  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.
caption: A roof truss of U-boat bunker "Valentin" is lifted into place (1944)
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