Large, heavily protected underground factories were constructed - as with the partly-buried Weingut I complex for Jumo 004 jet engine production - to take up production of the Me 262, safe from bomb attacks. A disused mine complex under the Walpersberg mountain was adapted for production of complete aircraft. These were hauled to the flat top of the hill where a runway had been cleared, and flown out. Between 20 and 30 Me 262s were built here. The war ended before this and other underground factories could reach meaningful output. Wings were produced in Germany's oldest motorway tunnel at Engelberg, to the west of Stuttgart. At B8 Bergkristall-Esche II at St. Georgen/Gusen, Austria, slave labourers of concentration camp Gusen II produced fully equipped fuselages for the Me 262 at a monthly rate of 450 units on large assembly lines from early 1945. Gusen II was known as one of the harshest concentration camps; the typical life expectancy was six months. An estimated 35,000 to 50,000 people died on the forced labour details for the Me 262.