[1] In 1915 he was mobilised as a member of the Territorial Force, serving in the East Surrey Regiment in France and Belgium.

[2] On 12 March 1917 he was awarded the Military Cross (MC) for gallantry for leading a successful raid on German lines.

During the Second World War, Thomas saw active service in France, Malaya, and Burma.

[4] In February, as a lieutenant colonel, Thomas took command of an ad hoc formation called "Tomforce" made up of troops from the 18th Infantry Division during the Battle of Singapore.

In 1945 he was appointed a Commander of the Order of the British Empire and awarded a Bar to his DSO, ending the war as a colonel.