John Clark was born in 1940 in Columbia, Missouri. He was commissioned through the Air Force ROTC program at the University of Missouri-Columbia on June 5, 1962. Clark graduated from Undergraduate Pilot Training and was awarded his pilot wings at Reese AFB, Texas, in August 1963. He next flew C-131 Samaritan transports with the 12th AeroMedical Transport Squadron at McGuire AFB, New Jersey, from October 1963 to June 1965. Clark then completed RF-4C Phantom II Combat Crew Training and served at RAF Alconbury, England, from June 1965 to October 1966. He began flying combat missions in Southeast Asia with the 11th Tactical Reconnaissance Squadron at Udorn Royal Thai AFB, Thailand, in October 1966. On March 12, 1967, Capt Clark was forced to eject over North Vietnam and was immediately captured and taken as a Prisoner of War. After spending 2,170 days in captivity, he was released during Operation Homecoming on February 18, 1973. He recovered from his injuries at the USAF Medical Center at Scott AFB, Illinois, and then went back to college through an Air Force Institute of Technology assignment at the University of Missouri-Columbia in October 1973. Clark then served as an instructor pilot at Vance AFB, Oklahoma, before leaving active duty on June 10, 1977. He spent time in the Missouri Air National Guard before joining the Air Force Reserve. He retired from the Air Force on January 12, 1992.