Mac followed in his father's footsteps into the military and served in the United States Marine Corps. He was a Lieutenant in the 1st Battalion 8th Marines during the peacekeeping mission to Beirut, Lebanon. In Season 6 it was mentioned that he served in the Gulf War and he is shown wearing the Southwest Asia Service Medal, although he himself has never spoken of the deployment. His decorations include the Silver Star, Bronze Star, Purple Heart, Navy & Marine Corps Commendation Medal and Navy & Marine Corps Achievement Medal. He was discharged in March 1992 at Camp Lejeune.