Weingut I

In 1944 the Third Reich began work on the construction of a partially underground bunker factory codenamed Weingut I in the forest known as the Mühldorfer Hart, slightly to the west of Mühldorf am Inn in Upper Bavaria. 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, 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 time-line.

Source: Wikipedia