The Leonberg concentration camp existed for one year, from April 1944 until April 1945. It was an outpost of the Natzweiler concentration camp in Alsace. The first or old Engelberg tunnel at Leonberg was opened for traffic in 1938 after three years of construction. It was part of Reich highway 39; with two tubes, each 300 meters long, it was the first highway tunnel in Germany. Starting in April 1944, these tunnels were used as a Messerschmitt AG factory for the production of the Düsenflugzeug