Thomas enlisted on 29th April 1899. He was 20 years and 5 months old. On 1st January 1902 he was appointed Lance Corporal, then shortly after gained promotion to the rank of Corporal. He re-engaged into the R.A.M.C. at Jersey 2nd January 1910, haven served his 1st period of engagement. On 10th August 1914 he gained promotion to the rank of Serjeant. Thomas entered the war in France on 14th August 1914, as part of the Regimental Medical Officer's team for the 1st Bn. Lincolnshire Regiment. His name appears on a list of R.A.M.C. personnel who were taken captive up to & including 31st December 1914 - (kindly provided by Steve Mattocks). He was taken to the German prisoner of war camp Cassel on 30th September 1914, then on to Ohrdruf on 27th November 1914. He was awarded the Distinguished Conduct Medal, along with 5 others, "in recognition of great devotion to duty and eminent services rendered by them when prisoners of war, during epidemics of Cholera and Typhus fever, at the Prisoner of War Camps in Gottingen and Ohrdruf, respectively." He was repatriated on 29th June 1915, during which time he gained promoted to the rank of Staff Serjeant on 9th May 1915. On 21st July 1915 he transferred to serve with the Mediterranean Expeditionary Force. On 10th September 1917 he was serving with No 68 General Hospital when he was serving under the rank of acting Serjeant Major, then on 18th November 1918 he was serving with No 78 General Hospital when his rank reverted back to his permanent rank of Staff Serjeant. He returned to the UK on 6th January 1919, and was discharged on 28th April 1920 on termination of 2nd period of engagement. At this time his home address was 76 St Peters Street, South Croydon, Surrey.