Serbian collaborationist organizations the Serbian State Guard (SDS) and the Serbian Border Guard (SGS) reached a combined peak size of 21,000 men, the Serbian Volunteers Corps (SDK), the party militia of the fascist Yugoslav National Movement "Zbor" lead by Dimitrije Ljotić reached 9,886 men, its members helped guard and run concentration camps, and fought the Yugoslav Partisans and the Chetniks alongside the Germans. In October 1941, the Serbian Volunteer Corps participated in the notorious massacre of Serbian civilians at Kragujevac by providing assistance in the arrest and delivering of hostages to the German Wehrmacht. The members of the Serbian Volunteer Corps had to take an oath stating that they would fight to death both Communists and Chetniks.