Infantry service Guyou was serving as an enlisted
Brigadier in the cavalry reserves when war began. On 3 September 1914, he was assigned the duties of mounted scout for the
46eme Régiment d'Infanterie. On 12 October, he was promoted to
Maréchal-des-logis. On 12 April 1915, he was transferred to
8eme Régiment de Chasseurs. On 20 December 1915, he was sent for pilot's training. He earned Military Pilot's Brevet No. 2697, awarded on 17 February 1916.
Promotions and awards On 25 January 1918, Guyou was promoted to
Adjutant. On 6 April, he was awarded the
Médaille militaire to accompany his
Croix de Guerre. He received a temporary commission as a
sous lieutenant on 1 June 1918. His career as an ace was capped with the receipt of the ''Légion d'honneur'' on 16 October 1918. ==Post World War I==