Wikipedia
Sonderdienst were the Nazi German paramilitary formations created in semicolonial General Government during the occupation of Poland in World War II. They were based on similar SS formations called Volksdeutscher Selbstschutz operating in the Warthegau district of German-annexed western part of Poland in 1939.
Sonderdienst were founded on 6 May 1940 by Gauleiter Hans Frank who stationed in occupied Kraków. Initially, they were made up of ethnic German Volksdeutsche who lived in Poland before the attack and joined the invading force thereafter. However, after the 1941 Operation Barbarossa they also included Soviet prisoners of war who volunteered for special training, such as the Trawniki men (German: Trawnikimänner) deployed at all major killing sites of the " Final Solution". A lot of those men did not know German and required translation by their native commanders. The Abteilung Sonderdienst (Department of Special Services) was subordinate to Oberkommando der Wehrmacht sabotage division under Colonel Erwin von Lahousen (1 September 1939 – July 1943), and Colonel Wessel Freytag von Loringhoven (July 1943 – June 1944).