Between 1939 and 1945 , the '' Ordnungspolizei '' maintained battalion formations , trained and outfitted by their main police offices within Germany . Specific duties varied widely from unit to unit and from one year to another , but one task was that of controlling civilian populations of the conquered or colonized countries . After the German invasion of the Soviet Union in Operation Barbarossa of 1941 , the Order Police joined the SS Einsatzgruppen in the massacres of Jews behind the German lines . The first mass killing of 3,000 Jews by the German police occurred in Białystok on 12 July 1941 in the territories of Poland annexed by the Soviet Union , followed by the Bloody Sunday massacre of 10,000-12,000 Jews by the Reserve Police Battalion 133 , perpetrated in Stanisławów ( now Ivano-Frankivsk , Ukraine ) on 12 October 1941 with the aid of SiPo and the Ukrainian Auxiliary Police . The shootings in Russia proper culminated in the Battalion 45 massacre of 33,000 Jews at Babi Yar . The Order Police battalions became indispensable in the implementation of the Final Solution after the Wannsee Conference of 1942 . They rounded up tens of thousands of Nazi ghetto inmates for deportations to extermination camps during the liquidation of the Jewish ghettos in German-occupied Poland , but also participated themselves in the killing of Polish Jews along with the Holocaust executioners known as Trawnikis . During Operation Reinhard mass murders were committed by Battalion 101 against women , children and the elderly in various locations including forced-labour camps and subcamps , most notably during the '' Aktion Erntefest '' of 1943 , the single largest German massacre of Jews in the entire war , with 42,000 victims shot in the execution pits over the bodies of others
Aktion Erntefest
Aktion Erntefest
Reserve Police Battalion 101