Complex sentence: He joined the Home Office in 1939, but served in the Royal Artillery in 1940 to 1941 before his appointment to posts in the Office of the Secretary of State in Cairo, and with UNRRA.
Split into simpler sentences: He joined the Home Office in 1939, and served in the Royal Artillery from 1940 to 1941. After his service, he was appointed to various posts in the Office of the Secretary of State in Cairo, and with UNRRA.