The Nazi mobile killing units that carried out mass shootings in Eastern Europe were called the Einsatzgruppen.
These units operated behind the German army during the invasion of the Soviet Union, which began on 22 June 1941. They were organized by the SS and police leadership and worked with local collaborators and other German authorities. Their victims included Jews, Roma, Communist officials, prisoners of war, and others targeted by Nazi racial and political policies.
The Einsatzgruppen murdered people in cities, villages, forests, and ravines. At Babyn Yar near Kyiv, for example, they and their collaborators killed more than 33,000 Jews on 29–30 September 1941. Their shooting campaigns were a central part of the Holocaust before extermination camps became the principal killing mechanism.