Tannenberg Phase 4 1–14 September 1914

Following the destruction of the encircled Russian 2nd Army at Tannenberg, the Germans pressed on towards the remaining Russian forces occupying East Prussia. After hearing news of this defeat, General Paul von Rennenkampf halted movement towards the Germans and was preparing to take up a more defensive position. His 1st Army was spread across the forested terrain around the Insterburg gap, but was now outnumbered by the Germans. General Hindenberg judged the northern part of the line was more secure because of the protection provided by the heavy fortifications at Königsberg. This gave him a surplus of troops that he deployed to the south in an attempt to outflank the Russian line, which had been somewhat isolated after trying to provide support for the 2nd Army before it was defeated. The battle began on this southern flank on 7 September but the Russians initially provided stronger resistance than expected.