on mobilization in august 1914, general auguste dubail was put in the charge of the first army, which comprised the 7th, 8th, 13th, 14th, and 21st army corps, two divisions of cavalry and one reserve infantry division. it was massed between belfort and the general line mirecourt-lunéville with headquarters at epinal. first army then took part, along with the french second army, in the invasion of lorraine. the first army intended to take the strongly defended town of sarrebourg. bavarian crown prince rupprecht, commander of the german sixth army, was tasked with stopping the french invasion. the french attack was repulsed by rupprecht and his stratagem of pretending to retreat and then strongly attacking back. on 20 august rupprecht launched a major counter-offensive, driving the french armies out. dubail was replaced in 1915. a frantic 1916 saw four different commanders command the first army; an even more frantic 1917 saw five different commanders at the helm (including françois anthoine during the battle of passchendaele). by the time of passchendaele, the french first army was composed of two corps - the 1st army corps (composed of 4 divisions) and the 36th army corps (composed of 2 divisions).