During World War II, the Nazi German were a sub-group of the "" (mobile killing squads) – up to 3,000 men total – usually composed of 500–1,000 functionaries of the SS and Gestapo, whose mission was to exterminate Jews, Polish intellectuals, Romani, and communists in the captured territories often far behind the advancing German front. "Einsatzkommandos", along with "Sonderkommandos", were responsible for the systematic killing of Jews during the aftermath of Operation Barbarossa, the invasion of the Soviet Union. After the war several commanders were tried in the Einsatzgruppen trial, convicted, and executed.