During World War One the Gorlice–Tarnów Offensive was initially conceived as a local offensive on the Eastern Front with the goal of relieving pressure on the Austro-Hungarians in the southern part of the front. Due to its success the offensive transformed into the Central Powers’ main offensive for 1915, causing the Russian lines to collapse. Because of the collapse, the Russian Army had to retreat far into Russian territory.
Mackensen planned to use his guns to blast aside the thin defenses between Gorlice and Tarnów, allowing his three armies then to burst through the Russian lines, with the German Twelfth Army driving onwards at the front, while the Austrian Third and Fourth Armies advanced in echelon on either side, protecting the flanks.
The Austro-Hungarian army had always been supranational, and professional officers made an effort to learn the languages of their men. Conrad himself, for instance, spoke seven languages. 1914 changed this. The professional officers were speedily wiped out. The new officers were men of a different stamp who had neither the will nor the opportunity to learn their men’s languages. Desertion began. By spring 1915, the Austrian army seemed to be on the verge of disintegration, and the process could seemingly only be halted if the Germans intervened.
The threat of Italian intervention against the Habsburg Monarchy made German help all the more urgent. When war began, Italy had declared neutrality, but as Austrian defeat succeeded Austrian defeat, the temptation for Italy to come into the war and seize Austrian territory was very strong. The matter was dragged out, partly to increase the terms Italy would get from the Entente, partly from domestic disputes, since the socialists and clericals were, on the whole, against joining in the war. But a coup d’état finally prompted Italian intervention.
Generals Ludendorff and Hindenburg would have preferred not to prepare a breakthrough in the center but to launch a double envelopment of the Russians from the Baltic and Carpathian fronts. They disfavored ‘ordinary victories’, which led only to Russian withdrawal to lines further east, and argued for cutting off the enemy from the great spaces of the Tsar's empire by a maneuver of encirclement. Though exercising command in the east, they were, however, subordinate to Falkenhayn and he overruled them.
Mackensen's operation order stressed the importance of a break-in which was rapid and deep enough to prevent the Russians bringing forward reserves to stem the flow. ‘The attack of Eleventh Army must, if its mission is to be fulfilled, be pushed forward fast... only through rapidity will the danger of the enemy renewing his resistance in the rearward positions be averted... Two methods are essential: deep penetration by the infantry and a rapid follow-up by the artillery.’ These orders anticipated the tactics which would be employed with such success against the British and French in 1918.
The Russian Army, for all its superiority of numbers, was in severe material difficulty. Between January and April, its divisions on the Eastern Front, except for the small number in the Caucasus, received only two million shells from the factories, at a time when preparatory bombardments with several hundred thousand shells were becoming the norm; worse, the output of the Russian arsenals was insufficient to provide soldiers with the most essential tool of warfare, a personal weapon. About 200,000 rifles were needed each month, to equip the new intakes of recruits, but only 50.000 were being produced.
There was an extensive amount of diversionary activity undertaken prior to Mackensen’s offensive, with attacks made by the Germans in the north and by the Austrians in the south in order to deflect Russian attention from the crucial sector. In any case the Russians ignored a series of intelligence reports drawing attention to the German build-up in the Krakow area, distracted as they were by their own plans for a Carpathian offensive. The Russians were also hampered by the continuing failure of the commanders of the South-West Front and the North-West Front to cooperate in any meaningful way.
When the guns blazed out, everything went according to plan as the heavy German and Austrian shells smashed through the Russians’ simple linear trench lines, killing and burying many. Those who ran for their lives were massacred by the shrapnel fire of the German field guns. By the time the infantry attacked it was a procession, as they smashed through the Dunajec and Biala line. The minimal Russian reserves were thrown into the bonfire and merely added to the flames.
A local success by the Russian Ninth Army, pushing Austrian General Karl von Pflanzer-Baltin back from the Dniestr to the Prut, was the only bright spot for Russia. But it was too remote to affect matters in Galicia, where both the Third and Eighth Armies lost heavily in the Battle of Sanok.
The Russian Third Army – or what was left of it – tumbled back in confusion all the way to the San River, the armies on either side of it being forced to conform or themselves be destroyed. Then the San River line was also breached, with the Germans pouring through, and it looked like Przemyśl would fall. The fortress was again under siege, this time by the Germans, who entered the city victorious. The Russians began in effect a ‘fighting retreat’.
The Central Powers advance continued and the city of Lemberg, today known as Lviv, was captured. All the Russian gains of 1914 had been swept away.
The Central Powers’ offensive attained much greater results than Ludendorff’s and Conrad’s enterprises in February of that year, although the forces allotted were not greatly different. It was partly a matter of weather: when Mackensen’s attack began, the roads were passable everywhere, which had not been the case in February, partly a matter of Russian weakness in matériel. The factor that lent Falkenhayn’s May offensive such dimensions of success was above all strategic.
Gorlice-Tarnów and Lemberg were cumulatively even more disastrous for Russia than Tannenberg. The Russians had to withdraw from Poland and Galicia in order to shorten their supply lines and consolidate new defensive positions. This was a severe blow to Russian morale.