In response to Adolf Hitler's plan to invade Poland on 1 September 1939, Heydrich re-formed the "Einsatzgruppen" to travel in the wake of the German armies. Membership at this point was drawn from the SS, the "Sicherheitsdienst" (Security Service; SD), the police, and the Gestapo. Heydrich placed SS-"Obergruppenführer" Werner Best in command, who assigned to choose personnel for the task forces and their subgroups, called "Einsatzkommandos", from among educated people with military experience and a strong ideological commitment to Nazism. Some had previously been members of paramilitary groups such as the "Freikorps". Heydrich instructed Wagner in meetings in late July that the "Einsatzgruppen" should undertake their operations in cooperation with the "Ordnungspolizei" (Order Police; Orpo) and military commanders in the area. Army intelligence was in constant contact with "Einsatzgruppen" to coordinate their activities with other units.