John H.Glenn entered the Naval Aviation Cadet Program in March 1942 and was graduated from this program and commissioned in the Marine Corps in 1943. After advanced training, he joined Marine Fighter Squadron 155 and spent a year flying F-4U fighters in the Marshall Islands.During his World War II service, he flew 59 combat missions. After the war, he was a member of Marine Fighter Squadron 218 on the North China patrol and served on Guam. From June 1948 to December 1950 Glenn was an instructor in advanced flight training at Corpus Christi, Texas. He then attended Amphibious Warfare Training at Quantico, Virginia. In Korea he flew 63 missions with Marine Fighter Squadron 311. As an exchange pilot with the Air Force Glenn flew 27 missions in the in F-86 Sabrejet. In the last nine days of fighting in Korea Glenn downed three MIG's in combat along the Yalu River.After Korea, Glenn attended Test Pilot School at the Naval Air Test Center, Patuxent River, Maryland. After graduation, he was project officer on a number of aircraft. He was assigned to the Fighter Design Branch of the Navy Bureau of Aeronautics (now Bureau of Naval Weapons) in Washington from November 1956 to April 1959, during which time he also attended the University of Maryland.In July 1957, while project officer of the F8U Crusader, he set a transcontinental speed record from Los Angeles to New York, spanning the country in 3 hours and 23 minutes. This was the first transcontinental flight to average supersonic speed. Glenn has nearly 9,000 hours of flying time, with approximately 3,000 hours in jet aircraft.
On February 20, 1962, Glenn piloted the Mercury-Atlas 6 "Friendship 7" spacecraft on the first manned orbital mission of the United States. Launched from Kennedy Space Center, Florida, he completed a successful three-orbit mission around the earth, reaching a maximum altitude (apogee) of approximately 162 statute miles and an orbital velocity of approximately 17,500 miles per hour. Glenn's "Friendship 7" Mercury spacecraft landed approximately 800 miles southeast of KSC in the vicinity of Grand Turk Island. Mission duration from launch to impact was 4 hours, 55 minutes, and 23 seconds.STS-95 Discovery (October 29 to November 7, 1998) was a 9-day mission during which the crew supported a variety of research payloads including deployment of the Spartan solar-observing spacecraft, the Hubble Space Telescope Orbital Systems Test Platform, and investigations on space flight and the aging process. The mission was accomplished in 134 Earth orbits, traveling 3.6 million miles in 213 hours and 44 minutes.