Fighting in Eastern Europe began with the first Austro-Hungarian invasion of Serbia in early August 1914. The number of Austro-Hungarian troops was far smaller than the 308,000-strong force intended when war was declared. This was because a large portion of the Austro-Hungarian 2nd Army had moved to the Russian Front, reducing the number of troops involved in the initial stages of the invasion to approximately 200,000. Forty percent of this force was composed of South Slavs living within Austro-Hungarian borders. On the other hand, the Serbs could muster some 450,000 men to oppose the Austro-Hungarians upon full mobilization. The main elements to face the Austro-Hungarians were the 1st, 2nd, 3rd and Užice Armies, with a combined strength of approximately 180,000 men. The Balkan Wars had only just concluded and Serbia was still recovering. Over 36,000 Serbian soldiers had been killed and 55,000 seriously wounded. Few recruits had been gained from the newly acquired territories, and the Serbian army had been stretched by the need to garrison them against Albanian insurgents and the threat of Bulgarian attack. To compound matters, the Serbian army was dangerously short of artillery, and had only just begun to replenish its ammunition stocks. Its supply problems also extended to more basic items. Many Serbian recruits reported for duty barefoot, and many units lacked any uniform other than a standard issue greatcoat and a traditional Serbian cap known as a "šajkača". Rifles were also in critically short supply. It was estimated that full mobilization would see some 50,000 Serbian soldiers with no equipment at all. The Austro-Hungarians, on the other hand, possessed an abundance of modern rifles and had twice as many machine guns and field guns as the Serbs. They also had better stocks of munitions, as well as much better transport and industrial infrastructure behind them. The Serbs had a slight advantage over the Austro-Hungarians: many of their soldiers were experienced veterans of the Balkan Wars and better trained than their Austro-Hungarian counterparts. Serb soldiers were also highly motivated, which compensated in part for their lack of weaponry.