Einsatzgruppen (mobile killing units) were German special duty units, composed primarily of SS and police personnel, assigned to kill Jews as part of the Nazi program to kill the Jews of Europe. During the invasion of the Soviet Union in June 1941, the mobile killing squads followed the German army as it advanced deep into Soviet territory, and carried out mass-murder operations. Wherever the mobile killing squads went they shot Jewish men, women, and children, without regard for age or gender. Mobile killing squads killed more than a million Jews and tens of thousands of Soviet political officials, partisans, and Roma (Gypsies).
US Holocaust Memorial Museum