Duncan Shields attended the United States Air Force Academy in Colorado Springs, Colorado. After graduating in 1976, he attended pilot and combat crew training on the KC-135 Stratotanker.
In 1983, Duncan attended Squadron Officers School and the Air Force Institute of Technology. He earned a Master of Science in Electrical Engineering with a focus in electro-optics.
Subsequently Duncan was a Developmental Engineer at the Air Force Electronic Warfare Center.
In the late 80s, Duncan spent time as a Major at the Air Command and Staff College.
While stationed at Plattsburgh AFB, Duncan continued to pilot the KC-135 as well as functioned in the roles of; instructor pilot, evaluator, flight commander, and operations officer. He was deployed to take part in Operation Desert Storm/Desert Shield.
As a Lt Col, Duncan was the 43 OSS Squadron Commander/43 OG Deputy group commander at Malmstrom AFB.
At his last duty station, Duncan was the Deputy Chief for Strategy Policy and Planning at the Air Mobility Command Headquarters. Duncan retired from the USAF in 1998.
After he retired, Duncan moved to Highlands Ranch with his wife, Celia, and their five children.