Engelberg tunnel

The Engelberg Tunnel is a motorway tunnel on the German A81 Autobahn (motorway) just to the west of Stuttgart on the outskirts of Leonberg. During World War II it was used as a Nazi forced labor factory for the manufacture and storage of aircraft parts.

The name is sometimes used to refer to the Old Engelberg Tunnel - which was Germany's second ever motorway tunnel - and sometimes used to refer to its successor, the completely rebuilt lower Engelberg Tunnel. Both travel under the Engelberg hill to the east of Leonberg on the Stuttgart to Heilbronn A81 motorway.

The original Engelberg twin tunnel was opened to traffic on 5 November 1938 after three years' construction. The 318m long twin tunnel stood on 'Route 39' of the network of motorways built during the German Reich and was Germany's first ever motorway tunnel.

During World War II both tunnels were closed to traffic in 1944 to be used as a Messerschmitt factory. Nazi slave labourers were brought to work in the factory from the Natzweiler-Struthof concentration camp in Alsace. In shifts lasting between 12 and 18 hours, "Zwangsarbeiter" [forced workers] assembled wings for Me 262 type aircraft. To provide extra production area, an extra floor was built in the tunnels. Total production area was 11,000m².

Around 3000 people were forced to work in the Engelberg factory. 374 died there.

Shortly before the end of the Second World War all the machinery was removed and the tunnels were blown up.

The first tunnel was returned to full working order between 1946 and 1950. The second was completed in 1961.

Each tube of the old tunnel was only wide enough to accommodate two lanes of traffic (with no hard shoulder). As traffic volumes rose, the tunnel became a bottleneck, especially for heavy goods vehicles. Traffic jams were not so much caused by the restriction to two lanes as the steep approach to the tunnel. Vehicles approaching from the north had to overcome a 6 per cent ascent. Lorries slowed significantly before reaching the tunnel causing long tailbacks.

...
Wikipedia