He graduated from Yale University, where he studied French history and was a member of the Berzelius Secret Society along with friends such as William Warren Scranton.
[14] On August 10, 1944, Dewey parachuted into southern France as the leader of a 10-man team from the United States Office of Strategic Services (OSS).
[15] Dewey arrived on September 4, 1945, in Saigon to head a seven-man OSS team "to represent American interests" and collect intelligence.
[15] Working with the Viet Minh, he arranged the repatriation of 4,549 Allied POWs, including 240 Americans, from two Japanese camps near Saigon,[16] code named Project Embankment.
Because the British occupation forces who had arrived to accept the Japanese surrender were short of troops, they armed French POWs on September 22 to protect the city from a potential Viet Minh attack.
[18] On September 26 because the airplane scheduled to fly Dewey out did not arrive on time at Tan Son Nhat International Airport, he returned for a lunch meeting with war correspondents Bill Downs and Jim McGlincy at the villa that OSS had requisitioned in Saigon.
Bluechel later recalled that Dewey had shaken his fist and yelled at three Vietnamese soldiers in French while driving back to headquarters.
Reportedly, Ho Chi Minh sent a letter of condolence about Dewey's death to U.S. President Harry S. Truman while also ordering a search for the colonel's body.
Dewey is not listed on the Vietnam Veterans Memorial in Washington, D.C. because the United States Department of Defense has ruled that the war officially started, from a U.S. perspective, on November 1, 1955, after the U.S. took over following the French defeat at Dien Bien Phu.
[23] Dewey is also remembered in an inscription on one of the walls in the National Cathedral, Washington, DC, which states that he was killed in action Indo-China 1945.