On his 19th birthday in January 1917, Fitzmaurice held the rank of Corporal, was an acting Sergeant, and commanded Platoon No. 13 of D Company, 7th Queen's. He was approved for a commission in May. On 8 June, Fitzmaurice left for England "to take up commission". He was sent for training to Cadet College and graduated to the 8th (Irish) Battalion, King's (Liverpool Regiment) as a Second Lieutenant on 28 November 1917. Fitzmaurice was then posted to the School of Military Aeronautics at Reading. 1 June 1918 Fitzmaurice began his "practical flying training" at Eastbourne Aerodrome. On 28 October 1918, having completed his elementary training at Eastbourne, Fitzmaurice was posted to the No. 1 School of Fighting and Aerial Gunnery at Marske-by-the-Sea, near Middlesbrough. He completed his training as a fighter pilot and was posted to sail to France on 11 November 1918, the day that the Armistice with Germany became effective. His sailing was cancelled when the Armistice was announced.