When he graduated from the
University of Denver in 1955, he was commissioned as an officer in the US Army. He later earned his master's degree in International Affairs at
George Washington University's
Elliott School of International Affairs. Mahaffey went on to a distinguished military career, one that saw him earn three Silver Stars, two Distinguished Flying Crosses and four Bronze Stars for valor in combat and a Distinguished Service Medal, the Army's highest non-combat award. He commanded a battalion in the
9th Infantry Division during the Vietnam War. In 1975 he assumed command the 2nd Brigade of the
101st Airborne Division. He was succeeded in command of the 2nd Brigade by a fellow future four-star general, then-Colonel
Colin Powell. He also commanded the
3rd Infantry Division from 1981 to 1983. Mahaffey's other assignments included Division Operations Officer for the 101st Airborne Division, Assistant Commandant of the
United States Army Infantry School; Deputy Commanding General of the
Combined Arms Combat Development Activity; and Deputy Chief of Staff for operations for the Army. Mahaffey was promoted to four star rank in 1985 at the age of 51, making him one of the youngest four-star generals ever. ==Death and burial==