His sailing was cancelled when the Armistice was announced. After the war Fitzmaurice married Violet "Bill" Clarke on his 21st birthday. He continued to serve in the Royal Air Force, flying the mails with 110 Squadron. He served in the "Army of Occupation" until 1919. In May 1919, he was selected to undertake the first night mail flight (Folkestone to Boulogne). In 1919, he was selected for a Cape to Cairo flight (which did not materialize). From September to November 1919, Fitzmaurice commanded the 6th Wing Working Party of the RAF. He was assigned the task of removing useful material from six aerodromes which had been deactivated. In December he was demobilized and spent most of the following 18 months selling insurance for the North British and Mercantile Insurance Company. In about May 1921, Patricia Fitzmaurice was born. She was the only child of Violet and James Fitzmaurice. Fitzmaurice was recalled in May 1921 after 18 months and was attached to 25 Squadron. He accepted a Short Service Commission for four to six years. In August 1921 Fitzmaurice resigned his RAF commission. Sometime during his service in the RAF, Fitzmaurice adopted the accent used by English officers. He apparently retained this distinctively non-Irish accent for the remainder of his life. His new accent may have helped his career in the RAF. In February 1922, Fitzmaurice joined the Irish National Army's Air Service following the formation of the Irish Free State. Early in 1923 he was promoted to Captain. On 25 October 1925 he was promoted Acting Commandant and was appointed second-in-command of the Irish Air Corps, with headquarters in Baldonnel. He was later promoted Commandant on 1 September 1927. Fitzmaurice made his first attempt to fly the Atlantic in 1927, when in the Princess Xenia (aircraft) (a Fokker F.VIIa aircraft) piloted by Captain Robert Henry McIntosh, who got financial backing from an American millionaire William Bateman Leeds and his co-financier Captain Anthony (Wilfred Heyman) Joynson-Wreford. Captain Joynson-Wreford was to have been the navigator on the flight but unfortunately had to stand down due to the recurrence of an old war injury. Having received the meteorological forecast indicating, that even though the first 200 miles off the Irish coast were poor, the rest of the route to America was clear, so they decided to proceed with the attempt. A large crowd watched their take off from Baldonnel at 1:30 p.m., however,