The Battle of Tannenberg, in which the Germans encircled and destroyed the Russian Second Army in late August 1914, effectively ended Russia's invasion of East Prussia before it had really begun.
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Overview
Russia invaded German territory with two armies: General Samsonov's Second Army in the southwest and General Rennenkampf's First Army in the northeast.
The two armies planned to combine and attack General Prittwitz's German Eighth Army, with Rennenkampf attacking from the front and Samsonov attacking from the rear.
This was the Russian plan, but Rennenkampf changed it after a bloody victory against the Eighth Army at the Battle of Gumbinnen. He paused to regroup his forces.
General Prittwitz, shaken by the Battle of Gumbinnen and fearful of encirclement, ordered a retreat to the River Vistula.
German Army Chief of Staff Helmuth von Moltke was furious at Prittwitz's decision and recalled him to Berlin, replacing him with the more aggressive combination of Paul von Hindenburg, who had been brought out of retirement at the age of 66, and Erich Ludendorff, who had distinguished himself at Liege.
Upon arriving in East Prussia on August 23, Hindenburg immediately reversed Prittwitz's decision to retreat. Instead, he authorized a plan of action prepared by Colonel Maximilian Hoffmann, Prittwitz's deputy chief of operations.
While Hindenburg and Ludendorff received much credit for the subsequent victory at Tannenberg, the actual plan of attack was devised in detail by Hoffmann.
General Prittwitz was shaken by the Battle of Gumbinnen and feared that he would be surrounded. He ordered a retreat to the River Vistula.
German Army Chief of Staff Helmuth von Moltke was furious when he heard this. He recalled Prittwitz and his deputy, von Waldersee, to Berlin. He replaced them with the more aggressive duo of Paul von Hindenburg and Erich Ludendorff.
Hindenburg arrived in East Prussia on August 23 and immediately reversed Prittwitz's decision to retreat. He authorized a plan of action prepared by Colonel Maximilian Hoffmann, Prittwitz's deputy chief of operations.
Hindenburg and Ludendorff received much credit for the subsequent victory at Tannenberg, but the actual plan of attack was devised by Hoffmann.
Meanwhile, General Samsonov was unaware that General Rennenkampf had paused to regroup at Gumbinnen. He assumed that Rennenkampf was still moving southwest.
Samsonov was also unaware of Hoffmann's plan or of its execution. He believed that his Second Army was on its way to pursue and destroy the retreating Eighth Army. He continued to direct his army of twelve divisions in a north-westerly direction toward the Vistula.
The Battle
On August 22, the bulk of Samsonov's forces reached the extremities of the German line. They fought and won small battles as they continued to advance into the German trap of encirclement.
On August 25, Ludendorff ordered General Francois to attack Samsonov's left wing at Usdau. Francois refused, saying that he needed more time to prepare his artillery.
Ludendorff and Hoffmann traveled to see Francois and repeated the order. Francois reluctantly agreed but said that he didn't have enough shells.
On their way back from meeting with Francois, Hoffmann was given two intelligence intercepts that had been sent by Rennenkampf and Samsonov. The intercepts were sent in the clear, meaning that they were not encrypted.
The first intercept from Rennenkampf revealed the distance between his and Samsonov's armies. It also detailed his First Army's marching plans, which did not include attacking Samsonov's Second Army.
The first intercept from Rennenkampf showed that the German Eighth Army would not have to worry about being attacked by the Russian First Army. The second intercept from Samsonov was even more remarkable.
Samsonov had attacked the heavily entrenched German XX Corps the day before, on August 24, at the Battle of Orlau-Frankenau. He had failed to defeat the Germans, but he believed that they were retreating to Tannenberg. As a result, he sent a message detailing his plans to pursue the Germans.
This information was invaluable to the Germans. It gave them a clear picture of the Russian forces and their plans. This allowed them to set a trap for Samsonov and destroy his army.
Hoffmann hurried after Ludendorff and Hindenburg with the intercepted messages. Ludendorff was skeptical of their authenticity, but Hindenburg was inclined to believe them because he knew about the personal quarrel between Rennenkampf and Samsonov.
Hindenburg and Hoffmann argued that Francois could wait for the arrival of artillery supplies before attacking Usdau. Ludendorff, however, wanted to assert his authority over Francois and insisted on the attack beginning as scheduled.
General Francois did not intend to attack without artillery support. He argued with Ludendorff and eventually attacked on August 27 with his I Corps. He quickly succeeded in taking Soldau to the Russian border, cutting off communication with Samsonov's center. Francois' forces confined Samsonov's left to the frontier.
Despite his success, Francois did not regain the trust of Hindenburg or Ludendorff, especially after they moved to Berlin to take over the direction of the war.
Ludendorff, fearing that Rennenkampf's forces might join the fray, ordered Francois to move back north. Francois ignored this order and instead moved his corps east to prevent Samsonov's center from retreating over the border.
Although this was disobedience of Ludendorff's order, it contributed to the sweeping victory that followed.
Helmuth von Moltke, the German Army Chief of Staff in Berlin, was also nervous about the German Army's prospects in the east.
He surprised Ludendorff by calling him and saying that he was sending a cavalry division and three corps from the west to bolster the Eastern Front. Ludendorff protested that the reinforcements were unnecessary, as they could be ill-afforded by the weakened German attack toward Paris.
Nevertheless, reinforcements were sent.
On August 25, after receiving the Russian radio intercepts, Ludendorff decided that Rennenkampf's forces were unlikely to attempt to join Samsonov.
He sent the two corps stationed at Gumbinnen south, where they met and engaged Samsonov's VI Corps, moving northwards at Bischofsburg the following day. Surprised and disorganized, both divisions retreated separately for the Russian border.
Ignoring warnings of a massed German advance moving south, Zhilinski directed Rennenkampf's First Army to the west to Konigsberg on August 26, a considerable distance from Samsonov's plight.
Given the degree of personal enmity between Rennenkampf and Samsonov, the former had no particular inclination to come to Samsonov's assistance.
Disaster struck Samsonov when Hoffmann and Ludendorff intercepted Zhilinski's unciphered order to Rennenkampf.
Ludendorff promptly dispatched Below from Bischofsburg to rejoin the German center and sent Mackensen south to meet up with General Francois. They joined in Willenberg, south of Bischofsburg, on August 29. Samsonov was now surrounded.
On August 28, Samsonov finally became aware of the peril he faced. His forces were dispersed, critically short of supplies, and his communications system was in tatters.
VI corps had already been defeated. Consequently, he ordered a general withdrawal on the evening of August 28.
Aftermath
Samsonov's forces were too disorganized to mount a successful defense. Many soldiers threw down their weapons and ran directly into the encircling German forces. Counter-attacks from the Russian border were weak and insufficient.
The Russians suffered a devastating defeat. Over 95,000 soldiers were captured, an estimated 30,000 were killed or wounded, and only around 10,000 of Samsonov's men escaped.
The Germans suffered fewer than 20,000 casualties and captured over 500 guns. Sixty trains were required to transport the captured equipment to Germany.
Samsonov, lost in the surrounding forests with his aides, shot himself. He was unable to face reporting the scale of the disaster to Tsar Nicholas II.
His body was subsequently found by German search parties and accorded a military burial.
Hindenburg and Ludendorff were celebrated as heroes in Germany. The victory at Tannenberg was so decisive, combined with later successes at the First and Second Battles of the Masurian Lakes, that Hindenburg replaced Erich von Falkenhayn as German Chief of Staff, bringing Ludendorff with him as his quartermaster general.
The victory was a major propaganda coup for Germany. The scale of the Russian defeat shocked Russia's allies, who wondered whether it signaled the defeat of the Russian army. However, this was not the case, as demonstrated by the lesser scale of German victories at the Masurian Lakes.
The sheer weight of the Russian army ensured its survival. Even so, no Russian army penetrated German territory again until the close of the Second World War in 1945.