Members of the Einsatzgruppen units at this point were drawn from the SS, the SD and the police.[16] They were used during the invasion of Poland to forcefully de-politicise the Polish people and kill members of groups most clearly identified with Polish national identity: the intelligentsia, members of the clergy, teachers, and members of the nobility.[16] When the units were re-formed prior to the invasion of the Soviet Union in 1941, the men of the Einsatzgruppen were recruited from the SD, Gestapo, Kripo, Orpo and Waffen-SS.[17] These mobile death squads were active in the implementation of the Final Solution in the territories overrun by the Nazi forces.[18]