Gary Thornton was born in Delano, California, in 1941. He enlisted in the U.S. Navy Reserve on September 26, 1959, and served at NAS Oakland, California, until 1961, and then at NAS Alameda, California, until November 1963. Thornton went on active duty at Naval Air Reserve Training Unit Jacksonville, Florida, on November 3, 1963, and was accepted into Naval Pre-Flight School in January 1965. He began Pre-Flight at NAS Pensacola, Florida, on February 17, 1965, and completed the program on June 26 of that year. He then attended Naval Aviation Officer School at NAS Sherman Field, Florida, graduating on November 5, 1965. Thornton then completed Radar Intercept Officer Training at NAS Glynco, Georgia, on February 4, 1966, and was commissioned an Ensign in the U.S. Navy on February 10, 1966. After one month of recruiting duty, he reported to VF-121 for Replacement Air Group training as an F-4 Phantom II RIO at NAS Miramar, California, completing the syllabus in August 1966. He then joined VF-96 at Miramar, and embarked aboard USS Enterprise for Southeast Asia in November 1966. Thornton began flying combat missions in December 1966 and was forced to eject over North Vietnam while flying his 45th combat mission and was taken as a Prisoner of War on February 20, 1967. After spending 2,205 days in captivity, he was released during Operation Homecoming on March 4, 1973. CDR Thornton attended Naval Postgraduate School at Monterey, California, from September 1973 to September 1975, and then flew P-3 Orions at NAS Moffett Field, California. He then completed a short tour with VP-47 before serving as Admin Officer for Moffett Field from January 1978 to June 1980. His next assignment was as Officer in Charge at NALF Crows Landing, California, where he served from June 1980 to June 1981, followed by Operations Officer at Moffett Field, from June 1981 to May 1982. CDR Thornton served as Officer in Charge of the Combined Service Support Program School at NAS Alameda, California, from May 1982 until his retirement from the Navy on September 1, 1991.

His Silver Star Citation reads:

For conspicuous gallantry and intrepidity while interned as a Prisoner of War in North Vietnam. On 25 February 1967, his captors, completely ignoring international agreements, subjected him to extreme mental and physical cruelties in an attempt to obtain military information and false confessions for propaganda purposes. Through his resistance to those brutalities, he contributed significantly toward the eventual abandonment of harsh treatment by the North Vietnamese, which was attracting international attention. By his determination, courage, resourcefulness, and devotion to duty, he reflected great credit upon himself and upheld the highest traditions of the Naval Service and the United States Armed Forces.