Ruffey was given command of the Third Army at the outbreak of war and charged with attacking along the line from Montmedy to Rocroi. Third Army consisted of IV, V and VI Corps, the 7th Cavalry Division and a group of three reserve divisions. His army came under heavy German pressure from mid-August, suffering a defeat at the Battle of the Ardennes, a part of the Battle of the Frontiers. On 23 August Ruffey warned his corps commanders not again to send infantry on bayonet charges without fire support from artillery or even small arms.