Thomas enlisted in the Citizens Military Force (Reserves) on 27 Dec 1940 and posted to 44th Infantry Battalion. He transferred to the A.I.F. on 17 May 1941 and was an original member of the unit, embarking aboard “S.S. ZEALANDIA” on 8 Dec 1941 for Timor as a Private in No 1 Sect, “A” Platoon. After the campaign on Timor, he embarked with the unit, for Australia aboard the Royal Dutch destroyer “Tjerk Hiddes” on 16 Dec 1942. After leave and reorganization he embarked with the unit as a Corporal in No 3 sect, “A” Troop for New Guinea aboard S.S. “DUNTROON” on 17 Jun 1943. He was appointed Lance Sergeant on 19 Jan 1944, wounded in action but remained on duty on 20 Mar 1944 and returned to Australia by plane on 31 May 1944. He attended a Small Arms Course from 25 Sept to 1 Dec 1944.
Thomas was Mentioned in Despatches, London Gazette, 8 Mar 1945 and in the Commonwealth of Australia Gazette, No 54-15 Mar 1945.
After further leave and reorganization, he embarked for New Britain aboard “TAROONA” on 9 Apr 1945 with the unit as a Lance Sergeant. He flew to Australia on 15 May 1945 to attend an Officer Cadet Training Unit from 21 May to 10 Sept 1945, commissioned as a Lieutenant on 9 Sept 1945. He transferred to Headquarters, South Australia on 9 Oct 1945 and then to Australia Staging Camp on 7 Jan 1946 and was discharged on 19 Jul 1946.
He was entitled to the 1939-45 Star, Pacific Star, War Medal and Australian Service Medal 1939-45, pictured below.