The use of concentration camp prisoners in the armament industry, which started in Austria at the Steyr-Münichholz camp in March 1942, led to the construction of numerous subcamps of the main concentration camp of Mauthausen. To the regional centers where subcamps were built, belonged the industrial areas of Vienna–Wiener Neustadt and central Upper Austria with its large industrial complexes. Together with »Reichswerke Hermann Göring« and »Steyr-Daimler-Puch AG,« the companies were mostly part of the rapidly expanding airplane and rocket industry, which had been transferred to Austria because of the latter's perceived »air safety.« These plants used prisoners in construction and pro-duction.
The relocation of armament factories to subterranean facilities started in fall 1943 and led to site selections for subcamps, which were located far away from the traditional war industry centers. They were chosen according to geological and traffic engineering criteria. The largest underground constructions were located near Melk, near Ebensee, and in Gusen. Together with the complex of Maut-hausen/Gusen, the camps of Ebensee and Melk developed into the largest concentration camps of Austria.