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.[9] Membership at this point was drawn from the SS, the Sicherheitsdienst (Security Service; SD), the police, and the Gestapo.[10][11] Heydrich placed SS-Obergruppenführer Werner Best in command, who assigned Hans-Joachim Tesmer [de] 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.[12] Some had previously been members of paramilitary groups such as the Freikorps.[13] 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.[14] Army intelligence was in constant contact with Einsatzgruppen to coordinate their activities with other units.[15]