For full details of Thomas' WW1 service and sources, see https://thefallenservicemenofsouthwestcountydurham.com/stephenson-t-w/

Thomas enlisted with the Army Reserve in Middlesbrough on 10.12.1915 aged 22 years and 1 month. He was mobilised on 29.3.1916 and joined the Royal Fusiliers with regimental number 10676.  On 10.8.1916, he was sent to France and posted to the 17th Battalion, Royal Fusiliers. 25.8.1916 transferred to the 22nd Battalion, Royal Fusiliers. Some time later he was assigned regimental number 9/79871. During the winter of 1916/17 he had spells in various Field Hospitals suffering from Scabies.  On 29.4.1917, he suffered a gun shot wound to the left thigh. He was treated by No 5 Field Ambulance and in No 24 General Hospital, Etaples. On 10.5.1917, he transferred to England. From 19.6.1917 t0 28.6.1917 he was on furlough at home with his parents in Butterknowle. He returned to France on 6.12.1917 and was posted first to the 2nd Battalion, then the 7th Battalion, Royal Fusiliers. On 26.1.1918, he was admitted to No 26 General Hospital with Trench Feet. He was transferred to the 15th (service) Battalion, Durham Light Infantry on 31.3.1918 and assigned regimental number 91960.

See https://thefallenservicemenofsouthwestcountydurham.com/stephenson-t-w/ for details of the 15th Battalion's campaigns during the spring and early summer of 1918, including on the Somme in May 1918. At the end of that month, Thomas was reported missing in action on 27.3.1918. As a prisoner with a penetrating gun shot wound to his right thigh, he died on 31.5.1918 in Bavarian Field Hospital No 28. He was buried initially at the Military Cemetery at Chateau Porcien (behind enemy lines) then at Sissonne British Cemetery when this was created after the Armistice.