After graduating from Dartmouth College in 1940, Braden enlisted in the British Army while the U.S. was still neutral in World War II, and he saw combat in Africa in the King's Royal Rifle Corps. When the United States entered the war, he was recruited by the U.S. Office of Strategic Services (OSS), the predecessor of the Central Intelligence Agency (CIA), and he was parachuted behind enemy lines into Nazi-occupied France. At the end of the war, with the encouragement of OSS Director William "Wild Bill" Donovan, who thought of Braden as a protégé, he and his OSS paratrooper compatriot Stewart Alsop wrote a journalistic book about the OSS, two years before it was replaced by Harry Truman with the CIA.