During World War II, the Nazi German Einsatzkommandos were a sub-group of five Einsatzgruppen mobile killing squads—up to 3,000 men each—usually composed of 500-1,000 functionaries of the SS and Gestapo, whose mission was to kill Jews, Polish intellectuals, Romani, communists and the NKVD collaborators in the captured territories often far behind the advancing German front.
After the outbreak of war with the Soviet Union known as Operation Barbarossa, the Red Army began to retreat so fast, that the large Einsatzgruppen had to be split into dozens of smaller commandos (Einsatzkommandos), responsible for systematically killing Jews and, among others, Soviet political activists behind the Wehrmacht lines. Several Einsatzkommando officers were tried and hanged after the war (see Einsatzgruppen Trial).
From June 1941 until the end of the war, the four Einsatzgruppen (A-D), together with their eager Eastern European auxiliaries killed around 1.5 million Jews in the occupied parts of the Soviet Union.
The method was first of all mass shootings. The Jews were captured or arrested, forced to dig their own graves or simply placed along large mass graves, and then shot so that they fell into the grave.
These commandos followed the troops when they were invading the various European countries, rounded up all of the Jews, shot them and dumped them into ditches.
Each squad shot for about one hour and was then replaced. The persons who still had to be shot were assembled near the place of the execution and were guarded. NUERNBERG MILITARY TRIBUNAL