Gros joined the army in 1913 and was serving with an artillery regiment when the war began. Wounded in action on 25 September 1915, he transferred to the French Air Service on 16 February 1916. After receiving a Pilot's Brevet on 28 May, he was posted to Escadrille HF41 on 22 October. In April 1917, he scored his first only only victory of the year. On 1 January 1918, Gros joined Spa154, downing 5 balloons and 3 more enemy aircraft before he was badly wounded on 15 September 1918.