November 9, 1915 – The Morava Offensive Operation was undertaken by the Bulgarian First Army between 14 October 1915 and 9 November 1915 as part of the strategic offensive operation of Army Group Mackensen against Serbia in 1915. Under the command of Lieutenant General Kliment Boyadzhiev the Bulgarians seized the fortified areas of Pirot, Niš and the valley of the river Morava. As a result the Serbian forces were compelled to retreat towards Kosovo. In the beginning due to the harsh weather and the tough terrain the Bulgarian advance was slow but despite the desperate resistance of the defenders, there was a Bulgarian breakthrough near Pirot in 10 days and the Serbs retreated to the Timok and the Bulgarian 1st Army chased them. The battle continued for 27 days and the Bulgarians penetrated up to 90 km deep into the enemy’s territory. The Serbs lost 6,000 men; 60 guns and huge amount of military equipment.