 As the weather had improved slightly in early November, reconnaissance flights were able to keep Mackensen and his commanders apprised of Serbian movements.As the Germans and their allies advanced, the Serbians retreated.Although the loss of Niš, Kragujevac, Kruševac, and Kraljevo had cost the Serbians a tremendous quantity of equipment and had made a retreat inevitable, the Serbian army retained its organizational integrity while its rearguards managed to hold off the oncoming forces of the Central powers.