Between 1939 and 1945, the Ordnungspolizei maintained battalion formations, trained and outfitted by their main police offices within Germany.[5][6] Specific duties varied widely from unit to unit and from one year to another,[7][8] but one task was that of controlling civilian populations of the conquered or colonized countries.[9] 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.