[4] Tidmarsh was commissioned as a second lieutenant in the 4th Battalion, Royal Irish Regiment (Special Reserve) on 23 April 1915.
24 Squadron, he was piloting an Airco DH.2 on 2 April 1916 when he scored his—and his squadron's—first victory, destroying a German Albatros two-seater and killing its crew of Karl Oscar Breibisch-Guthmann and Paul Wein.
[6] He was promoted to lieutenant on 1 July 1916,[10] and appointed a flight commander with the temporary rank of captain on 16 August 1916.
[14] With the outbreak of World War II imminent, he was recommissioned as a flying officer in the Administrative and Special Duties Branch of the Royal Air Force Volunteer Reserve on 31 August 1939.
[15] He was promoted to temporary squadron leader on 1 September 1942,[16] and relinquished his commission due to ill-health on 20 January 1944.
[17] He died in a Dublin nursing home on 27 November 1944,[18] just 18 days after his brother Gerard, who was serving as a major in the British Army.