Between 1939 and 1945, the Ordnungspolizei maintained military formations, trained and outfitted by the main police offices within Germany.[13][14] Specific duties varied widely from unit to unit and from one year to another.[15] Generally, the Order Police were not directly involved in frontline combat,[16] except for Ardennes in May 1940, and the Siege of Leningrad in 1941.[17] The first 17 battalion formations (from 1943 renamed SS-Polizei-Bataillone) were deployed by Orpo in September 1939 along with the Wehrmacht army in the invasion of Poland.[14] The battalions guarded Polish prisoners of war behind the German lines, and carried out expulsion of Poles from Reichsgaue under the banner of Lebensraum.[18] They also committed atrocities against both the Catholic and the Jewish populations as part of those "resettlement actions".[19] After hostilities had ceased, the battalions - such as Reserve Police Battalion 101 - took up the role of security forces, patrolling the perimeters of the Jewish ghettos in German-occupied Poland (the internal ghetto security issues were managed by the SS, SD, and the Criminal Police, in conjunction with the Jewish ghetto administration).[20]