Sandford arrived at the Western Front in France as a Captain in February 1915, and by May 1916 had been promoted to the rank of Major and was Officer Commanding of the 94th Battery, RGA, leading it in action at Hebuterne, Artois, at the start of the Somme Offensive on 1 July 1916 until he was posted to command 355 Battery in September 1918. Following the war he resigned his commission and moved to Ethiopia in 1920, where he became an advisor to Ethiopian Emperor Haile Selassie.
Sandford fled Ethiopia in early 1936 once it became clear that the 1935 Italian invasion of Ethiopia would succeed. Once back in England, Sandford maintained contact with the exiled Emperor, Haile Selassie, who was based in Bath. In August 1939, the head of the Middle East Command in Cairo, General Sir Archibald Wavell, summoned Sandford for duty. Wavell made Sandford a colonel and put him in charge of the Ethiopian Section in Middle East intelligence. Sandford immediately began liaising with resistance groups in Ethiopia, and in January 1940 toured the French- and British-held territories bordering Ethiopia to solicit support for a planned Allied-backed Ethiopian revolt against the Italians. The British plan to foster and assist the Ethiopian revolt was called Mission 101. Overall, Sandford's tour was relatively successful, and so upon his return to Cairo he selected the team he would use to implement Mission 101 and drew up two plans of action: Scheme A, which dealt with military preparations and the British role, and Scheme B, which focused on the propaganda methods to be used. As soon as Italy declared war on 10 June, Sandford and his team swung into action implementing his plan. Sandford oversaw Mission 101 until the arrival of Orde Wingate. Later in the war and in its immediate aftermath, Sandford served again as advisor to Emperor Selassie, both in military and political roles.
Sandford held various posts in the Ethiopian government, retiring as Director General of the Addis Ababa Municipality in 1951. Meanwhile, his wife, Christine, established the Sandford Community School in Addis Ababa. The school still exists and is considered to be one of the best International Schools in Ethiopia. After his retirement, Sandford devoted all his energies to farming the plot of land given him by Haile Selassie at Mulu near the townDerba, 60 km north of Addis Ababa, planting among others, coffee and plum trees, and building stables for cattle. Sandford died at the farm on 22 January 1972. After Selassie was overthrown by the Derg regime in 1974, the farm was nationalized, and more stables were built to increase the number of cattle. Within a few years however, the farm had ceased to be operational. Today, the farm plot is leased by a Dutch horticulture farm. The summerhouse built by Sandford is being renovated to its original state. Some parts of the construction had to be replaced but efforts are being made to keep the original material in place. The walls still contain the original cedar wood.
