On August 26, 1914, the German 8th Army, under the leadership of Paul von Hindenburg and Erich Ludendorff, strikes with lethal force against the advancing Russian 2nd Army, led by General Aleksandr Samsonov, in East Prussia during the opening weeks of the First World War.

In the middle of August 1914, much sooner than had been anticipated, Russia sent two armies into East Prussia, while Germany, according to its war strategy, had the bulk of its forces concentrated to the west, against France. The Russian 1st Army, under General Pavel Rennenkampf, advanced to the northeastern corner of East Prussia, while Samsonov’s 2nd Army made headway into the southwest, planning to join with Rennenkampf’s men and pin the outnumbered German 8th Army between them. After a Russian victory in the Battle of Gumbinnen on August 20, however, Rennenkampf paused to regroup his forces.

Meanwhile, change was afoot behind the German lines: Helmuth von Moltke, chief of the German general staff, chose to replace the previous leader, Maximilian von Prittwitz, after the latter issued a misguided order for a German retreat to the River Vistula, against the advice of his corps commanders. Hindenburg, a retired general of great stature, and Ludendorff, who had just led the German capture of the Belgian fortress of Liege, arrived in East Prussia and immediately authorized an aggressive counter-action against the Russians, previously planned by a senior staff officer in the region, Colonel Max Hoffmann.

Separated by the great Masurian Lakes, the two Russian armies were unable to effectively communicate with each other as to their movements, a circumstance that would prove deadly. Though Ludendorff succumbed to nerves initially, delaying the start of the German attack by one day, Hindenburg was able to calm his subordinate—not for the last time in what would become a fabled partnership. On August 26, after intercepting wireless messages from both Samsonov and Rennenkampf, the Germans were able to take Samsonov’s army by surprise with the force of their attack near the village of Tannenberg, to the southwest of the Masurian Lakes. The delay in starting the attack had given Samsonov’s forces more time to advance deeper into the sack formed by the German divisions enveloping them from both sides, the strength of which Samsonov consistently underestimated. After three days of battering by German artillery, Samsonov’s troops began their retreat; more German forces cut off their path and a massive slaughter ensued. In the first hours of August 30, confronting the reality of his army’s collapse, Samsonov went into the forest, away from his staff, and shot himself.

In total, over 30,000 Russian soldiers were killed and some 92,000 taken as prisoners in the Battle of Tannenberg—named thus by the Germans in vengeful remembrance of the village, where in 1410 the Poles had defeated the Teutonic Knights. By the end of August, Russia’s ambitious advance in East Prussia in August 1914 had achieved at least one of its goals, albeit at a tremendous cost: two German corps had been removed from the Western to the Eastern Front in order to confront the Russian menace. Though the two corps had not arrived in time to play a role in the Battle of Tannenberg—which would remain the greatest German triumph of the war against Russia on the Eastern Front—they would also be unable to aid their comrades at the Battle of the Marne in early September, when German forces advancing towards Paris were decisively defeated by British and French troops in a crucial victory for the Allies.