sentences:  He served as a captain in the Ayrshire Yeomanry and took part in the Normandy Landings, being awarded the Military Cross in 1945 for his survey work between Allied and enemy lines.After the war, he returned to Oxford to complete his degree and was an active member of the Oxford University Dramatic Society.In 1947, O'Brien joined the Dominions Office, then was at the Commonwealth Relations Office from 1947 to 1949.