Forrester graduated from West Point in June 1979 and was commissioned as a Second Lieutenant in the U.S. Army. He entered the U.S. Army Aviation School in 1979 and was designated an Army aviator in September 1980. He was subsequently assigned as an instructor pilot at the Aviation School and as the Aide-de-Camp to the Deputy Commanding General of the U.S. Army Aviation Center. In 1984, he was assigned to the 25th Infantry Division (Light), Schofield Barracks, Hawaii, where he served as a platoon leader, aviation company operations officer, and an assault helicopter battalion operations officer. After completing a master of science degree at the University of Virginia in 1989, he was assigned as a flight test engineer and as the research and development coordinator with the Army Aviation Engineering Flight Activity at Edwards Air Force Base, California. In June 1992, he graduated from the U.S. Naval Test Pilot School and was designated an experimental test pilot. In 1992, he was assigned as an engineering test pilot at the U.S. Army Aviation Technical Test Center, Fort Rucker, Alabama. Other military schools include the Army Parachutist Course, U.S. Army Ranger School, the Combined Arms Services Staff School, and the Command and General Staff College.
Master Army Aviator, he has logged over 3000 hours in 49 different aircraft.