On 8 September 1914, Masson re-enlisted in his old unit. After being transferred to the 36eme Regiment d'Infanterie for a short while, Masson began military pilot's training at Pau. He earned his Military Pilot's Brevet on a Caudron on 10 May 1915. He was then assigned to Escadrille 18, which was operating Caudrons. In September 1915, he received additional training, learning to fly Nieuports. He was then forwarded to a Nieuport squadron, Escadrille 16, in April 1916, and passed through to start instructing at Cazeau on the 16th. He was in this assignment only two months, checking into the famed Lafayette Escadrille, Escadrille N124, on 16 June 1916. Though he never became an ace, Masson did manage the remarkable feat of having his Nieuport 17's engine cut out while in a dogfight and still downing his German opponent, gliding to safety near the French front lines afterwards. His hasty departure from the wrecked airplane saved him from the German artillery fire that was rained down upon it. By the time Masson departed N124, he was an Adjutant.
