The 1915 Gorlice–Tarnów offensive was the largest military operation of the First World War.
Initially planned as a minor tactical maneuver to relieve pressure on Austro-Hungarian forces, the Gorlice–Tarnów offensive evolved into a massive, 70-day campaign. It shattered Russian lines, forced a retreat across Galicia, and resulted in over 1.5 million casualties, marking a decisive turning point in the Eastern Front's strategic landscape.
In early 1915, the Austro-Hungarian Army faced a dire situation. Having suffered casualties equal to half its initial strength, it struggled to hold the Carpathian passes against Russian advances. General Franz Conrad von Hötzendorf, the Austro-Hungarian chief of staff, eventually threatened a separate peace unless Germany provided reinforcements. German Chief of Staff Erich von Falkenhayn, seeking to permanently diminish Russia's offensive capacity, agreed to a joint operation. He formed the new 11th Army, commanded by August von Mackensen, utilizing German divisions trained in Western Front assault tactics and heavily supported by artillery.
The offensive began on 2 May 1915, following a devastating bombardment by heavy mortars and field guns. The German 11th Army, supported by the Austro-Hungarian 4th Army, broke through Russian defenses near Gorlice. Despite desperate Russian counterattacks, the Central Powers advanced rapidly, capturing Sanok by 11 May and Lemberg by 22 June. The operation forced the Russian Empire into a total strategic retreat, eventually leading to the evacuation of Warsaw and the loss of the Polish salient. By the time the offensive concluded, the Central Powers had pushed Russian forces back to the lines held in August 1914.
The scale of the conflict was unprecedented. Approximately 4.5 million men were involved over 70 days, resulting in more than 1.5 million total casualties. Estimates suggest 170,628 Russian troops and 140,420 Central Powers soldiers died during the operation. While the offensive failed to knock Russia out of the war, it inflicted the largest defeat on the Russian Empire, forcing its army to switch entirely to strategic defense. The campaign's success was attributed to the Central Powers' overwhelming artillery superiority and the systemic failures of the Russian command, which struggled with poor coordination and severe shortages of ammunition.
Source: Gorlice–Tarnów offensive
