Retired as a Colonel in the United States Marine Corps. During World War II, he was a pilot-instructor and test pilot. During the Korean War, he flew 85 combat missions after being called back to active service in 1952. Was commissioned a Brigadier General in the California Air National Guard in 1966 and continued to serve after he began his acting career. Along with
James Stewart, he held the highest active military rank of any actor in history. McMahon was the highest-ranking officer to become an actor, and Stewart was the established actor who achieved the highest rank. Both were decorated combat aviators.
