After defeating the Russians, German General Hermann von Francois convinced the German commander of the Eighth army, General Maximilian von Prittwitz, to launch an attack against the Russian First Army, led by General Paul von Rennenkampf, at Gumbinnen. Although Rennenkampf's army fought well, they were defeated and forced to retreat 8 km (around 4.9 miles). Due to this retreat, German General August von Mackensen decided to attack the Russians with help from German General Otto von Below. However, the Russian's were alerted by Francois's attack and used artillery to wreck havoc on General Mackensen's army, forcing him and General Below to withdraw 24 km (around 14.9 miles). General Maximilian von Prittwitz panicked after the successful Russian counter - attack and ordered a general withdraw to the River Vistula. The German Chief of Staff, Helmuth von Moltke, was furious at General Prittwitz and replaced him with General Paul von Hindenburg.