Fletcher aspired to become an astronaut, and joined the Air Force Reserve Officer Training Corps. In 1974, he earned a Bachelor of Science degree in mechanical engineering, graduating with top honors. After graduation, he joined the U.S. Air Force. After flight training in Oklahoma, he was stationed in Alaska where he served as a F-4E Aircraft commander and NORAD Alert Force commander. During the Cold War, his duties included commanding squadrons to intercept Soviet military aircraft. In 1980, as budget cutbacks were reducing his squadron's flying time, Fletcher turned down a regular commission in the Air Force. He left the Air Force with the rank of captain, having received the Air Force Commendation Medal and the Outstanding Unit Award.