McClintock first served in Egypt from November 1914, as a private in the Ceylon Planters' Rifle Corps, however he was soon commissioned as a second lieutenant in the West Lancashire Brigade, Royal Field Artillery, and was promoted to temporary lieutenant on 5 July 1915. He was seconded for duty with the Royal Flying Corps on 4 April 1916, and was appointed a flying officer. He first served as an observer/gunner in No. 2 Squadron RFC, before training as a pilot, and being appointed a flying officer on 4 August. On 1 January 1917 he was appointed a flight commander with the temporary rank of captain. On 28 June his promotion to lieutenant in the Royal Field Artillery was made substantive, while remaining seconded to the RFC. In July he was posted to No. 64 Squadron RFC, flying the Airco DH.5 fighter. The squadron moved to France in October, and took part in the battle of Cambrai, flying low-level ground attack missions. The squadron replaced their DH.5s with the SE.5a in March 1918. McClintock gained his first aerial victory on 10 March 1918, driving down an LVG C reconnaissance aircraft over Marquion. On the afternoon of 23 March he destroyed a Pfalz D.III over Pronville, and an Albatros D.V over Biache. The following day he destroyed another Type C over Le Transloy, and finally on 2 April another D.V over Fricourt. On 20 April he was appointed a temporary major, to serve as commander of No. 3 Squadron RAF. McClintock was awarded the Military Cross which was gazetted on 21 June 1918. His citation read:
Post-war career
McClintock was granted a permanent commission in the RAF, with the rank of captain, on 1 August 1919. From 1920 he served at the No. 3 School of Technical Training at RAF Manston, while living in Birchington-on-Sea. On 22 June 1922Flight Lieutenant McClintock was flying a Sopwith Snipe at RAF Northolt, practising for a relay race to be held at the RAF's Annual Aerial Pageant at Hendon Aerodrome, when his aircraft crashed and he was killed.
Personal life
McClintock married Mary Gordon Laird at the Church of the Holy Trinity, Kensington Gore, London, on 20 December 1916. They had two children: John Arthur Peter McClintock, who served as a flight lieutenant in the Auxiliary Air Force, and was killed in action during World War II, and Pamela Mary McClintock, who was less than four months old at the time of her father's death.