On August 26, 1914, Russian and German forces began the Battle of Tannenberg. As part of the initial Russian campaign against the Germans during the war, Tannenberg would result in utter catastrophe for the Russian forces. Inadequate supply lines due to an underdeveloped rail system in Russian territory and differences in the gauge of rail used in Russia and that used in Western Europe plagued the Russian forces. Further complications arose with compromised communications with the Russian armies. Shortages of communication cables forced the used of wireless communication between the frontlines and the commanders in the rear; however, the Russian code system had been broken by the Germans and new code books were in short supply (only two of the three commanders during the campaign possessed one), resulting in many transmissions being made in the clear in the hope that they wouldn't be intercepted. Insufficient intelligence/reconnaissance regarding German positions and troop movements further hindered the Russians.

By the end of August, the battle was over and Germany emerged victorious. A force of 150,000 Germans had met a larger force of 250,000 Russians and devastated them. For the loss of nearly 14,000 of their own killed or wounded, the Germans inflicted 78,000 killed or wounded on the Russians and captured a further 92,000 men. The Russian Second Army had been annihilated and its commander, General Alexander Samsonov, committed suicide in disgrace. German Generalfeldmarschall Paul von Hindenburg would rise to prominence as a direct result of his command during the decisive German victory during the Battle of Tannenberg.