Einsatzgruppen were mobile killing squads of the Sicherheitspolizei and Sicherheitsdienst in World War 2. The followed around Nazi forces and killed targets that they were assigned. The Einsatzgruppen were first employed in Austria in March 1938, but their mission and performance there are still a mystery. Seven of the units(approx. 4200 men) followed the German invasion force into German invasion of Poland in September of 1939. They murdered Poland's elite: aristocrat, the intelligentsia, and priest, as well as many Jews while they were rounded up and herded into Jewish Ghettos. Five Units totaling 3,000 men also followed the Wehrmacht(German Army) during its invasion of the USSR in June of 1941 (operation Barbarossa) with orders to kill all Jews as well as Soviet political commissars. By November of 1941 as many as 600,000 Jews had been liquidated. Einsatzgruppen were also used against Soviet partisans, though these operations were often a cloak for helping to implement Hitler's Final Solution. It was planned that six units should be in the United Kingdom following its invasion, codenamed Sealion, which never took place.