Weingut I (English: Vineyard I) was the codename for a construction project, begun in 1944, to create an underground factory complex in the Mühldorfer Hart forest, near Mühldorf am Inn in Upper Bavaria, Germany. Plans for the bunker called for a massive reinforced concrete barrel vault composed of 12 arch sections under which Messerschmitt Me 262 jet engines would be manufactured in a nine-storey factory.
Upon completion these were to be sent to a similar installation in the area of Landsberg am Lech (codename Weingut II), where the final assembly of the aircraft was to take place. This network of underground factories was intended to ensure the production of the Me 262 at a time when the Allies had already gained control of the German airspace.
Despite it being increasingly clear to the organizers of the project that it would never be finished in time to make a difference in the war, the construction of Weingut I was approved on a 6-month timeline. Of a total of 10,000 workers who worked on the project, 8,500 were forced laborers and inmates of the Mühldorf concentration camp network. Of these more than 3,000 died of overwork, underfeeding, and SS brutality. By the war's end, only 7 of the planned total of 12 bunker sections had been built, and construction of the factory itself had not begun.
After the liberation of the area and its associated camps in May 1945, control of the construction site fell to the US Army, which made extensive studies of its innovative construction techniques before demolishing all but one section of the main bunker in 1947. Today the bunker grounds are a listed monument. Occasional tours of the site are offered by a Catholic nonprofit group in Mühldorf.
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