Fought from 26–30 August 1914, the Battle of Tannenberg demonstrated the strength of German organization and training and the weaknesses of its Russian counterpart. The generals of the two Russian armies invading Prussia barely spoke to one another; field communications were addressed through the military governor of Warsaw, and actions on the ground were bereft of any coordination. The Germans, taken unawares by the Russian invasion and seemingly on the run, had the flexibility to immediately change commander and implement a complete reversal of strategy, resulting in a comprehensive victory. Germany’s superior communication, mobility and tactics, such as the stalling of Rennenkampf while encircling the Russian Second Army, ensured their success. Later, as Germany moved further away from their home ground, the poorly maintained roads on the eastern front severely affected supply lines, making them lose their advantage.