Bernhard R. Kroener; Rolf-Dieter Muller; Hans Umbreit (2003). Germany and the Second World War. Vol. 5: Organization and Mobilization of the German Sphere of Power, Part 2: Wartime Administration, Economy, and Manpower Resources 1939-1941. Clarendon Press. p. 56. ISBN978-0-19-820873-0. Retrieved 12 October 2015.