In 1944 the Third Reich began work on the construction of a partially underground bunker factory codenamed Weingut I (English: Vineyard I) in the forest known as the , 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.