[4] He served in Sierra Leone 1898–99 (later known as the Hut Tax War), for which he received the East and West Africa Medal.

After the outbreak of the Second Boer War in October 1899, he was appointed on the Staff of the army in South Africa, and took part in a number of engagements and operations.

[4][5] He became Assistant Commissioner for the Anglo-French Boundary Commission in the East of Niger in late 1902, with the local rank of captain.

[6] After taking part in the Kano-Sokoto expedition which brought the Emirs in Nigeria under British control in 1903, he became Commander of the Ordnance Survey of Scotland in 1904.

[5] Foulkes served in World War I as Commander of 11th (Field) Company, taking part in the First Battle of Ypres in 1914 before becoming Britain's chief advisor on gas warfare in 1915 and General Officer Commanding the Special Brigade responsible for Chemical Warfare and Director of Gas Services in June 1917,[5] for which he was promoted to the temporary rank of brigadier general, taking over from Henry Fleetwood Thuillier.