Army Group F
In July 1944, German defenses began to fail. After the failure of Operation Draufgänger (Daredevil) – a 1944 anti-partisan operation in Montenegro, Yugoslavia, and Northern Albania – three divisions of the "Narodnooslobodilačka vojska Jugoslavije" (the People's Liberation Army of Yugoslavia) (NOVJ) – managed to cross the Ibar River to the east and threaten the main railroad lines. After the failure of Operation Rübezahl in Montenegro in August 1944, two additional NOVJ divisions broke through the German blockade, successfully entrenching themselves in western Serbia. Army Group F command responded by deploying additional forces: the 1st Mountain Division arrived in Serbia in early August, followed by the 4th SS Panzergrenadier Division from the Thessaloniki area.