Image's from
 Bart Vanderveen's book "Historic Military Vehicles Directory"
Reinhard Frank " Lastkraftwagen der Wehrmacht "
Udo Paulitz "Österreichs Feuerwehrveteranen - Fahrzeuge 1930 -70"

The 640 series replaced the Steyr 440 models in production during 1937. A total of 3780 were made until 1941 , nearly all for the German Army.  Various body types were mounted on this versatile chassis wich , like its predecessors , was characterized by its car-type front end with the spare wheels mounted on idler hubs ,thus serving as belly support wheels. The command/staff car version had choachbuilt convertible bodywork. 
The ambulance could accommodate four stretcher or eight sitting cases.