Roald Dahl worked for Shell in Tanzania before joining the Royal Air Force.
At the time, the territory was known as Tanganyika, a British-administered territory in East Africa. Dahl arrived there in 1938 after completing his education and began working for the Shell Petroleum Company. His job took him to remote areas and gave him experiences that later informed his autobiographical writing.
When the Second World War began, Dahl left his commercial career and entered military service. He first served as a fighter pilot with No. 80 Squadron, flying in the Middle East and North Africa.
The geographic name can cause confusion: Tanganyika became part of Tanzania in 1964 after uniting with Zanzibar. For a modern country-name answer, Tanzania is the standard answer, while Tanganyika is the historical name of the territory where Dahl worked.