The Russian armies crossed into East Prussia with their goal as Koenigsberg. At first the battle appeared to go well for the Russians, with the German's first counterattack repulsed on August 20. General Maximilian Prittwitz[?], the theatre commander, was sacked when he attempted to completely abandon East Prussia to the Russians.
While replacements were en route, the 8th Army's Chief of Operations[?], Max Hoffmann[?], redeployed the army. Hoffmann's plan left a screening force to delay the Russian 1st Army (under General Pavel Rennenkampf[?]) which was approaching from the east, and set a trap for the Russian 2nd Army (under General Alexander Samsonov[?]) which was moving up from the south.
The German field commander, General Hermann Francois[?], allowed the 2nd Army to advance, and then cut them off from their already tenuous supply route. This forced massive surrenders and the almost complete destruction of the 2nd Army near Frogenau[?]. However, General Erich von Ludendorff, the chief of staff for new theatre commander Field-Marshal Paul von Hindenburg dated the official dispatch reporting the victory from the nearby village of Tannenberg, and the battle is thus known to history. In 1410, an ancestor of Hindenburg had fallen in an earlier battle near Tannenberg.
The German victory compelled Rennenkampf to withdraw his army from East Prussia, and thus cleared German territory of invaders. The Russians remained on the defensive along the German front for the rest of the war.