Elliot See and Charlie Bassett were the prime crew for Gemini 9. On February 28, 1966, they were flying in a NASA T-38 trainer to visit the McDonnell plant in St Louis, where their spacecraft was in assembly. See misjudged his landing approach, and in pulling up from the runway, hit Building 101 where the spacecraft was being assembled. Both astronauts were killed, and 14 persons on the ground were injured. As a result, the Gemini 9 backup crew became the prime crew, and all subsequent crew assignments were reshuffled. This ended up determining who would be the first man on the moon.…
From the NASA official Gemini program history, On the Shoulders of Titans":
One bright winter morning, the last day of February 1966, the Gemini IX foursome checked into Ellington Air Force Base, Texas, for flight clearance to St. Louis in two dual-seat T-38 jet aircraft. They planned to spend several days practicing on the rendezvous simulator at the McDonnell plant. At Ellington, the four fliers learned that weather in St. Louis was gloomy: 180-meter overcast, visibility 3 kilometers, rain, and fog, with little change expected. Instrument flight rules would be required. See called the St. Louis air traffic controllers, saying he would see them in a couple of hours. He and Cernan discussed the different runways at Lambert Field in St. Louis. See then climbed into the front seat of one T-38, with Bassett easing into the back seat. Stafford and Cernan got into the other plane. They took off from Ellington at 7:35 a.m. See and Bassett led, with Stafford and Cernan flying wing position.
Reaching St. Louis just before 9 o'clock, See radioed the Lambert Field control tower and learned that the overcast had lifted to 240 meters since his earlier call, but the visibility had dropped to 2.4 kilometers. Light snow flurries now mixed with the rain and fog. As the aircraft descended through the overcast, the pilots found themselves too far down the runway to land. See elected to keep the field in sight and he circled to the left underneath the cloud cover. Stafford followed a missed approach procedure and climbed straight ahead into the soup to 600 meters, intending to make another instrument approach. He landed safely on his next attempt.
Meanwhile, See had continued his left turn. The aircraft angled toward McDonnell Building 101, where technicians were working on the very spacecraft See and Bassett were scheduled to fly. Apparently recognizing that his sink rate was too high, See cut in his afterburners and attempted a sharp right turn; but it was too late. The aircraft struck the roof of the building and crashed into a courtyard. Both pilots were killed.
NASA named a seven-man board to investigate the accident. Led by Astronaut Alan B. Shepard, Jr., the board looked into all aspects of the tragedy - aircraft maintenance, pilot experience, medical histories, and weather conditions. Shepard's group listened to testimony from everyone who had anything to say, sifted the wreckage for clues, and drew conclusions. They found nothing wrong with the aircraft; it had functioned properly to the moment of impact. Within the past six months, See and Bassett had renewed their instrument flying certificates. Before and during the flight, both men had been in good physical and mental condition, as attested by medical examinations and by reported pre- and in-flight conversations. Furthermore, See was reputed to be an excellent test pilot. Careful, judicious, and technically competent, he should never have crashed at all. Weather appeared to have been the major contributing cause, and pilot error prompted by a desire not to lose sight of the field had carried them too low.
On Wednesday, 2 March 1966, Spacecraft No. 9, on its way to the flight dock for shipment to Cape Kennedy, passed an American flag flying at half-mast at the McDonnell plant. The next day, Elliot See and Charles Bassett, attended by their fellow astronauts, were buried in Arlington National Cemetery across the Potomac from the Nation's capital.
NASA assigned the Gemini IX prime crew positions to Stafford and Cernan, marking the first time in the agency's manned space flight history that a backup crew had taken over a mission. On 21 March James Lovell and Edwin Aldrin were given the backup duties. There would be no delay in the launch schedule.
First Launch: 1966 June.