Central Powers attack Serbia

On the afternoon of 6 October 1915, or 23 September by the Julian calendar then used in Serbia, hundreds of German and Austro-Hungarian guns thundered along the whole northern border of Serbia, from Romanian Orsova on the Danube to Višegrad on the Drina. The day before, the artillery had begun ranging; now the bombardment proper began. On the same day the first Austro-Hungarian units crossed to the Serbian bank of the Drina and the Sava. The army group of Field Marshal August von Mackensen began the fourth invasion of Serbia in this war. This time the Serbs faced not only Austria-Hungary but also Germany, and within a few days Bulgaria was to join them.

The road to Constantinople

After three failed expeditions in 1914, which ended in defeat on the Kolubara, Austria-Hungary did not have the strength to defeat Serbia on its own. From the spring of 1915, however, the chief of the German General Staff, Erich von Falkenhayn, had been considering a new offensive. His main aim was to open an overland route from Germany to Turkey. Through Serbia ran the railway from Hungary through Belgrade, Niš and Sofia to Constantinople, and the Turks, defending themselves against the Allies at Gallipoli, were in ever greater need of German ammunition. When in the summer the Russian front fell back far to the east, the Germans could at last release troops for the Balkans. At the beginning of September Bulgaria concluded an alliance with them and undertook to attack Serbia together with them.

Command of the whole expedition was taken by Mackensen, the victor of Gorlice. On 20 September he arrived in Temesvár in southern Hungary. The plan envisaged an advance from two directions. From the north, across the Sava and the Danube, the German Eleventh Army of General Max von Gallwitz was to strike opposite Smederevo and Ram, together with the Austro-Hungarian Third Army of General Hermann Kövess, with its main forces at Belgrade. A few days later the Bulgarian First Army was to advance from the east, and the Bulgarian Second Army was to enter Macedonia and cut the Serbs’ railway to Salonika. According to the Austrian official history, Mackensen’s group and the Bulgarian Second Army together numbered 350 battalions and 1,400 guns against 275 Serbian battalions and 654 guns.

Mackensen did not want to wait. The Bulgarian mobilisation was dragging on, some Austro-Hungarian units were still on their way, and the Eleventh Army was asking for more bridging equipment. But autumn was approaching, and with it the košava, a violent east wind that could tear away the pontoon bridges on the Danube. Entente troops were beginning to arrive at Salonika, and Greece could still side with Serbia until the king dismissed Venizelos. On 4 October Mackensen set the start of the offensive for 6 October, and the crossing of the main forces for the night of 6–7 October.

Serbia in a vice

Serbia found itself in a hopeless position. Its army had not recovered from the losses of 1914 or from the typhus epidemic which in the winter and spring had killed tens of thousands of people. From the middle of September it was clear that Bulgaria was preparing for war. The Serbian command, in which, owing to the illness of Vojvoda Radomir Putnik, his deputy, Lieutenant-Colonel Živko Pavlović, played an ever greater role, wanted to strike at the Bulgarians before they completed their mobilisation. The British official history states that the Serbs were dissuaded from this intention by Lord Kitchener and the Foreign Secretary, Sir Edward Grey, and the Russians were equally opposed to it. The Entente still hoped to keep Bulgaria on its side, or at least neutral.

The Serbs therefore had to defend themselves on two fronts at once and divided their army into two almost equal parts. In the north remained the First Army of Vojvoda Živojin Mišić in Mačva and on the Drina, the Belgrade defence troops of General Mihailo Živković, and the Third Army of General Pavle Jurišić Šturm, strung out along the Danube. According to the Austrian official history, Živković had on the 50-kilometre sector at Belgrade only 20 third-levy battalions, that is the oldest reservists, and 75 guns. They were supported by the few heavy naval guns of the British mission of Admiral Ernest Troubridge and a few French guns. The Serbian staff expected the main blow across the Sava, between Obrenovac and Šabac, while the carefully concealed concentration of German troops opposite the mouth of the Morava was barely noticed by its airmen.

The first day

Shells of every calibre, including the heaviest mortars, rained down on Belgrade, Smederevo and the Serbian fortifications on the rivers. Smederevo was set ablaze, and the riverside districts of Belgrade were turned into ruins. The British correspondent Gordon Gordon-Smith, who was then in Niš, later wrote that in the first 48 hours more than 50,000 shells fell on Belgrade. This figure comes from contemporary accounts and is hard to verify. The British official history of the Macedonian campaign dates the start of the bombardment to 6 October, while the Austrian official history writes of the artillery ranging as early as 5 October.

That same day the Austro-Hungarian Landsturm, the territorial reserve of older age groups, entered Serbia from the west. The group of General Rudolf Streith crossed the Drina north-east of Bijeljina, but got stuck in the riverside thickets and backwaters and in the evening had to beat off Serbian counter-attacks. The group of General Béla Sorsich crossed the Sava under fire at Jarak, west of Šabac, and formed a small bridgehead, which it held despite attacks by the Serbian Danube Division. The Austro-Hungarian river monitors Szamos and Una, which supported this attack, came under fire from Serbian artillery near Šabac as they then sailed down the Sava, and Szamos was damaged. On the Danube, German patrol boats ferried the first soldiers of X Reserve Corps to the Serbian bank near Ram, and near Orsova the Austro-Hungarian group of General Artur Fülöpp feigned a crossing to distract the Serbs.

These were only preliminary moves. On the night of 6–7 October pontoons carrying the main forces set out onto the Sava and the Danube at Belgrade, at Ram and at the island opposite Kostolac. After three days of fighting, on 9 October, Belgrade was in the hands of the Central Powers’ forces, and on 14 October Bulgaria declared war on Serbia.