 It became increasingly clear to both Potiorek and Putnik that Austro @-@ Hungarian supply lines were over @-@ extended and so , on 1 December , Potiorek ordered the Austro @-@ Hungarian 6th Army to stop and wait for the 5th Army to secure its supply lines east of the Valjevo railway , resulting in a short pause to all Austro @-@ Hungarian military operations . Mišić exploited this brief respite by withdrawing the Serbian 1st Army a full 19 kilometres ( 12 mi ) from the front line and ensured that his soldiers had an opportunity to rest . The Serbian Army then converged around Mount Rudnik , where it received long @-@ promised supplies from its allies via the Niš – Salonika railroad . Putnik 's confidence in the ability of his army to launch a counterattack was restored . On 2 December , he ordered his forces to attack the Austro @-@ Hungarians all along the front and informed his officers that the offensive was to have the specific purpose of improving Serbian morale . Determined to play his part , the aging Serbian king , Peter I , took a rifle and accompanied his troops to the front . The Serbian offensive caught the Austro @-@ Hungarians by surprise , and at the time that the attack was launched they were holding a large military parade through the streets of Belgrade . The Austro @-@ Hungarians now found themselves defending along an over @-@ extended front as Potiorek had just begun strengthening his left flank , leaving the front line very lightly held . Potiorek knew that he could avoid a serious reversal on the battlefield by preventing the Serbian 1st Army from reaching the watershed of the Kolubara and Morava rivers , but the Serbs were confident . They discovered that the Austro @-@ Hungarians had failed to adequately prepare for a Serbian counterattack , as their artillery was positioned well behind the front line . This meant that the Austro @-@ Hungarian defenders would be unable to use their heavy guns to break up any Serbian advance . Rested and resupplied , the Serbs pushed forward towards Belgrade . By the night of 2 December , the Serbian 1st Army pushed several kilometres past Austro @-@ Hungarian lines , taking a large number of prisoners and inflicting heavy casualties on the Austro @-@ Hungarians . The 2nd and 3rd armies captured a number of important positions on high ground , while the Užice Army met fierce resistance but was ultimately able to push the Austro @-@ Hungarians back . 
