Schirra was a Navy test pilot who was accepted into the Mercury program in 1959. He was assigned the third orbital flight (which he called Sigma 7) in October 1962, notable for its duration of 9 orbits and proximity to a high altitude nuclear test.
He flew a second mission in December 1965. Gemini 6A was a replacement mission meant to rendezvous with Gemini 7, but was threatened by a launch failure. Schirra saved the mission by not ejecting himself and fellow astronaut Thomas Stafford, allowing the launch to repeated three days later.
In October 1968 he commanded Apollo 7, the first manned Apollo flight, spending 11 days in orbit. The crew were struck down by colds and the mission was notable for their rebellion in refusing to wear helmets on reentry and the live television broadcasts.
Walter Schirra was the only pilot to fly in each of the first three manned US space projects. His family report he died of natural causes. He was 84.