Complex sentence: O'Neil served as a combat flier with the U.S. Air Force during the Korean War from 1950 to 1953; and was a member of the American Legion and the Veterans of Foreign Wars.
Split into simpler sentences: O'Neil served as a combat pilot with the U.S. Air Force during the Korean War from 1950 to 1953. He was a member of the American Legion and the Veterans of Foreign Wars.