He began his career as a flying ace during the First World War, credited with five aerial victories.

He went to France in January 1915, and served as an infantryman on the Western Front until 2 December 1915, before being commissioned into the Welsh Regiment.

He claimed his first two victories in September 1917 while flying an Airco DH.5, destroying an Albatros D.III on the 25th near Cambrai, and another on the 28th at Bugnicourt, France.

A quarter-hour later, he joined with squadron-mates Russell Winnicott, Loudoun MacLean, and Frank Harold Taylor in driving another down out of control.

6 Squadron RAF, operating Royal Aircraft Factory R.E.8s and Bristol F.2 Fighters from Mosul, Iraq; he was Mentioned in Despatches on 19 April 1921.

[3] Thomas returned from foreign service to begin attending RAF Staff College on 1 May 1923.

On 1 September 1928, he began instructing cadets at the Royal Air Force College Cranwell.

[3] Once again posted overseas, Thomas began attending the Command and Staff College, Quetta on 24 December 1931.