Maunoury joined the army on September 7, 1914. Wounded in action while serving with the infantry, he transferred to the French Air Service on June 2, 1916. He scored his first victory as an observer with Escadrille C64. Reassigned to F16 on January 27, 1917, Maunoury was selected for pilot training and received a Pilot's Brevet on June 7, 1917. As a fighting pilot, he joined N152 on September 19, 1917 but did not score any victories until the summer of the following year. During 1918, he shot down 8 balloons and 2 German two-seaters.

Chevalier de la Légion d'Honneur
"Officer of high moral values. Severely wounded in the infantry where he was remarkable because of his audacity. He refused an assignment to auxiliary service and entered aviation at his request as an observer. After having shot down one enemy plane he was transferred to pursuit aviation where he has never ceased to demonstrate the noble qualities of spirit, energy and bravery. On September 15, 1918, in the course of a patrol, he flamed two enemy observation balloons. Two wounds, three enemy planes an six balloons shot down. Four citations." Chevalier de la Légion d'Honneur citation, October 9, 1918