Russian army and then moving to confront the second army was now at risk. A retreat to the Vistula could allow both Russian armies to combine. Eventually, Prittwitz changed his mind and decided instead to attack the Russian Second Army. A change from facing an army to the east, to an army in the south had been rehearsed by the Germans during war games. François's I Corps, joined by the 3rd Reserve Division, would move by train to the west of XX Corps. The I Reserve Corps and XVII Corps would withdraw westwards. In the meantime, Samsonov was delayed in his advance because of the lack of good railways and roads, and Rennenkampf was slow to pursue the withdrawal because of his losses and limited supplies. As Mackensen commented, "I had the strong impression that my corps had not been outfought, nor had it suffered such heavy losses. In complete calm and good order and without any interference by the enemy, it made its withdrawal." Prittwitz's panic affected Moltke, who feared that Berlin itself could now be threatened by the advancing Russians. On 21 August, Moltke decided to replace Prittwitz and his chief of staff Georg von Waldersee. Paul von Hindenburg and Erich Ludendorff assumed their roles on 22 August. Prittwitz became the first army commander to be dismissed in World War I. References Further reading Conflicts in 1914 Battles of the Eastern Front (World War I) Battles of World War I involving Germany Battles of World War I involving Russia East Prussia History of Kaliningrad Oblast 1914 in the Russian Empire 1914 in Germany August 1914 events