As a Generaloberst, commanded the German Eighth Army before the war, owing his position more to connections during peacetime than military genius. His sizable girth earned him the nickname Der Dicke, the 'Thick One.' Nonetheless, in the opening stages of the war, he found himself facing two Russian armies commanded by General Jilinsky, which held a four-to-one advantage over Prittwitz's forces.
Prittwitz was not Germany's brightest star, but did recognize talent among his staff. While his Chief of Staff, Waldersee, was more yes-man than advisor, one young staff officer, Lieutenant Colonel Max von Hoffmann, had the talent for command. Hoffmann and Prittwitz planned draw the Russian army commanded by Rennenkampf onto East Prussian soil and defeat it, then turn south to the other Russian army commanded by Samsonov.
General Francois, commander of the German I Corps would have no Slav on Prussian soil and so, attacked, driving the Russians to within 5 miles of their own border. Francois' action could not be adequately supported by the rest of the Eighth Army and resulted in the 'losing' battle of Gumbinnen. To Prittwitz's credit, when his subordinates urged him to press on the attack, he wisely chose to pull back and regroup. This regrouping made the 'victory' of Tannenburg possible, though he is seldom given any of the credit.
Though the Battle of Gumbinnen was hardly a disaster, Moltke used the occasion to replace Prittwitz and Waldersee with Hindenburg and Ludendorff on 20 August 1914. Prittwitz accepted the replacement without complaint. Hoffmann remained.
Among those serving in Prittwitz's Eighth Army were:
I Corps: von Francois
XVII Corps: Mackensen
XX Corps: Schotlz
I Res. Corps: Otto von Below