Now here’s a rarity for this stage in the War: a plan that worked. A hundred years ago today, as mentioned only yesterday, German, Austro-Hungarian and Bulgarian forces invaded Serbia on two fronts. Within two months, the country had been conquered and most of the invasion’s limited objectives achieved, at which point the invaders secured their gains and redeployed resources back to other fronts. The attack’s only failure lay in allowing the remains of the Serbian Army to retreat into Albania, but chasing it across the mountains would have risked heavy casualties in a largely symbolic cause, and it would be a long time before Serbian forces troubled the Central Powers again. So what was the secret of the year’s only complete offensive success?
The answer is that there was no secret. For once, the offensive tactics and technology of 1915, efficiently used, found circumstances ideal for their success. The offensive method in question, breakthrough tactics, has been described before, and amounted to massive concentration of men and firepower against a single point of the enemy defence. Breakthrough tactics had failed against well-prepared German defences on the Western Front and, after achieving initial successes during German offensives on the Eastern Front, they had fallen foul of extended supply lines and failed again. Serbia was different.
First of all, Serbia was barely able to defend itself. After the campaigns of 1914 had left its citizen army decimated, exhausted and short of every conceivable supply need, the country had been promised major reinforcement by Britain and France – but squabbles between the two had delayed help beyond usefulness. Serbian leaders had known for months that the invasion was coming, and that Bulgaria would take part, but Britain and France had also vetoed a Serbian plan for a preemptive summer strike against Bulgaria, which was still considered a potential ally in London and Paris. So the Serbian Army – some 200,000 typhus-ridden, hungry troops, all desperately short of ammunition and artillery support – could only take up its positions and wait for the hammer to fall.
It was a big hammer, deployed for generally sound strategic reasons. Austria-Hungary wanted to finish the job so poorly begun in 1914, and Bulgaria wanted territory it had failed to secure at the end of the Balkan Wars, but German military involvement took a wider perspective. German chief of staff Falkenhayn saw the removal of Serbia as a means to open up land communications with the Ottoman Empire and with its new Bulgarian allies. Once the Pless Convention had committed Bulgaria to the attack, Falkenhayn overruled the inevitable protests from Ludendorff and transferred forces from the Eastern Front to the Balkans. Come October, Serbia’s ragged defenders faced 300,000 efficiently concentrated, well-equipped and supported attackers, commanded by German Field Marshal Mackensen, star of the year’s Eastern Front offensives and the acknowledged master of breakthrough tactics.
When the hammer fell, with Austro-German attacks from the north and Bulgarian from the southeast, Serbian resistance crumbled very quickly. Once the government realised that Allied help wasn’t going to arrive, and even before the failure of General Sarrail’s unconvincing attempt to intercept the Bulgarians from Salonika, the campaign as a whole became a matter of retreat and pursuit. With no second line defences to overcome, and no problems with supply lines, the combined invasion force could deliver, within the limits of a relatively small theatre, the Holy Grail that had tormented Joffre and eluded Ludendorff – total victory through the shock and awe of breakthrough tactics.
The Serbian campaign of late 1915 makes a grimly fascinating story, and I’ll be having a word about it in weeks to come, but for now just an academic point: it took a small war within the War, in which defenders effectively fought with one hand tied behind their backs, for one of the period’s most efficient commanders to achieve the only clear-cut victory in Europe throughout 1915. So today marks the centenary of the exception that proved the rule.