In 1914, Thomas was working in Malaya as a civil engineer. At the outbreak of the war he returned to Scotland and enlisted. Perhaps because of his experience working in a tropical climate he was selected to serve in British East Africa. He enlisted in May 1915 and arrived in Mombasa, British East Africa in June of 1915.
He was initially a Lieutenant in the King’s African Rifles. At the outbreak of the war, the King’s African Rifles (KAR) was a three-battalion regiment consisting of a small number of British officers and approximately 2,300 Africans from various British colonial territories. While posted with the 3rd Battalion King’s African Rifles (3/KAR) Thomas saw action in several battles. His actions in the battle of Longido West on September 20, 1915 resulted in his being awarded the Military Cross. He was transferred to the Royal Engineers in the spring of 1916 as a Lieutenant and latterly acted as Captain while Lieutenant Colonel A.A. McHarg was on extended leave in 1917. In addition to being awarded the Military Cross, Thomas was twice mentioned in despatches by his commanders: on May 8, 1916 by Lieutenant General Jan Smuts and on October 11, 1917 by Lieutenant General Jakobus van Deventer.
Thomas Wilson wrote a series of letters from East Africa while he was serving with the King’s African Rifles and later with the Royal Engineers. Eight of these letters remain and are transcribed here. He started his African posting in Nairobi and eventually travelled as far south as Kilwa Kivinje. which is just south of Dar es Salaam. His letters are presented and transcribed here and are interspersed with accounts of the major actions in which he took part.