Rennenkampf and the Russian First Army were the first to encounter the German Eighth Army, winning the Battle of Gumbinnen. The defeat led the German High Command to dismiss von Prittwitz and his chief of staff, replacing them with General (later Field Marshal) Paul von Hindenburg and General Erich Ludendorff. Hindenburg and Ludendorff arrived on the Eastern Front and decided to attack Samsonov's advancing forces with the full weight of the Eighth Army. Hindenburg and Ludendorff were strengthened in making this decision by intercepted Russian wireless communications, which indicated that Rennenkampf and the Russian First Army could not reach the proposed battle in time to be of assistance, and by an intercepted order from Samsonov, showing the movement of his forces. The armies made contact on August 22 and for six days the numerically superior Russians had some success. However, by August 29 the Germans had surrounded Samsonov's Second Army in the woods between Allenstein and Willenberg. The rout that followed was named the Battle of Tannenberg by Hindenburg, to compensate for a defeat of the Teutonic Knights by the Kingdom of Poland and the Grand Duchy of Lithuania at the same location five centuries earlier.