Thomas enlisted in to the Reserve on 2 Jul 1941 and was posted to 5th Works and Parks Company, Royal Australian Engineers (RAE) on 19 Jul 1941 as a Draftsman. On 30 Jan 1942 he was transferred to RAE Headquarters and detached to 20th Army Field Company, RAE on 29 Mar 1942. He returned to HQ, RAE on 9 Apr 1942 and entrained for 5th Military District (Western Australia) on 17 Apr 1942. Whilst in WA he transferred to the A.I.F. on 5 Mar 1942 and transferred to 1st Australian Commando Training Battalion at Canungra, Qld on 25 Feb 1943. He joined the unit on 15 May 1943 and embarked with the unit for New Guinea as a Trooper aboard S.S. “DUNTROON” on 17 Jun 1943 and returned to Australia with them aboard “TAROONA” on 3 Sept 1944.
After leave and reorganization, he embarked for New Britain aboard “TAROONA” on 9 Apr 1945 with the unit as a Trooper. He transferred to 22nd Infantry Battalion on 26 Dec 1945 and returned to Australia on 6 Mar 1946.
He was discharged on 26 Mar 1946.
He was entitled to the 1939-45 Star, Pacific Star, War Medal and Australian Service Medal 1939-45, pictured below. He is now also entitled to the Australian Service Medal 1945-75 with a clasp "S.W.Pacific".