After completing two years of Aeronautical Engineering, John entered naval flight training in 1952. He was designated a naval aviator and comminssioned in the U.S. Marine Corps in 1954. During his Marine career, he served in numerous billets including tours as a fighter pilot, helicopter pilot, and flight instructor (in Naval Air Training Command). He attended the U.S. Naval Test Pilot School at Patuxent River, and after completion servered as project test pilot for three years on numerous fixed and rotary wing aircraft programs. He flew 59 missions in Vietnam in the McDonnell Douglas F4B Phantom.