Following the Austro-Hungarian invasion of Serbia, the First Army was put under the command of General Petar Bojović. It acted as a strategic reserve in the area of Aranđelovac during the Battle of Cer, but most of its divisions were sent to support the Second and Third armies actively engaged in the battle. The army conducted a successful crossing of Sava and performed an offensive into Syrmia (then part of Austria-Hungary) but was recalled when Second invasion of Serbia (also known as the Battle of Drina) began. The army had the decisive role in the battle conducting a strong counterattack against the Austro- Hungarian 6th army. It was engaged in some of the fiercest fights of the whole Serbian theatre at Mackov kamen, which ended in a bloody stalemate. After a month-long period of trench warfare, in November 1914, the Austro-Hungarian Army began the third invasion of Serbia (also known as the Battle of Kolubara). During the defensive part of this battle this army was in the most difficult situation due to heavy casualties from the Battle of Drina and acute lack of artillery ammunition. It was at this point that general Živojin Mišić, who was previously the Aide of Commander in Chief of Serbian Army, (Vojvoda/Duke -equivalent of Field Marshal Radomir Putnik), was made commander of this army, as Bojović was wounded. He restored morale and discipline (which had started to waver) in the army, by insisting on a deeper withdrawal before the Austro-Hungarians, all the way to Gornji Milanovac.