"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 Main Security Office (RSHA); and after his assassination, under the control of his successor, Ernst Kaltenbrunner.