Before the invasion of Russia in June 1941, four Einsatzgruppen were formed, designated with the letters A, B, C, and D. Each Einsatzgruppe was subdivided into a group staff and several "Einsatz-" and "Sonderkommandos". Each was attached to an army group, a group of several German armies, except Einsatzgruppe D. Einsatzgruppe D was assigned to the Ilth Army which later became a part of a 4th army group after the Germans reached the Caucasus.
The following is reprinted here from the evidence on the organization of the Einsatzgruppen: a photocopy of a large chart which was exhibited in the courtroom throughout the trial, an Einsatzgruppen report dated 11 July 1941, and an affidavit of defendant Ohlendorf.