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 murder 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. Organization of the Einsatzgruppen Einsatzgruppen () were paramilitary groups originally formed in 1938 under the direction of Reinhard Heydrich – Chief of the SD, and Sicherheitspolizei (Security Police; SiPo). They were operated by the Schutzstaffel (SS). The first Einsatzgruppen of World War II were formed in the course of the 1939 invasion of Poland. Then following a Hitler-Himmler directive, the Einsatzgruppen were re-formed in anticipation of the 1941 invasion of the Soviet Union. The Einsatzgruppen were once again under the control of Reinhard Heydrich as Chief of the Reich Security Main Office (RSHA); and after his assassination, under the control of his successor, Ernst Kaltenbrunner. Hitler ordered the SD and the Security Police to suppress the threat of native resistance behind the Wehrmacht's fighting front. Heydrich met with General Eduard Wagner representing Wilhelm Keitel, who agreed to the activation, commitment, command, and jurisdiction of Security Police and SD units in the Wehrmachts table of operations and equipment (TOE); in the rear operational areas, the Einsatzgruppen were to function in administrative sub-ordination to the field armies in order to effect the tasks assigned them by Heydrich. Their principal task (during the war), according to SS General Erich von dem Bach, at the Nuremberg Trials: "was the annihilation of the Jews, Gypsies, and Soviet political commissars". They were a key component in the implementation of the "Final Solution of the Jewish question" (German: Die Endlösung der Judenfrage) in the conquered territories. These killing units should be viewed in conjunction with the Holocaust. The military commanders knew the task of the Einsatzgruppen. The Einsatzgruppen depended upon their sponsoring army commander for billet, food, and transportation. Relations between the regular army and the SiPo and the SD were close. Einsatzgruppen commanders reported that the understanding by Wehrmacht commanders of Einsatzgruppen tasks made their operations considerably easier. For Operation Barbarossa (June 1941), initially