Mercury Astronaut
I was testing a P-51 fighter in Minneapolis when I spotted this object. […] It looked like a saucer, a disk. About the same time, I realized that it was suddenly going away from me – and there I was, running at about 300 miles per hour. I tracked it for a little way, and then all of a sudden the damn thing just took off. It pulled about a 45 degree climbing turn and accelerated and just flat disappeared.
About his 19 December, 1951 sighting. In his 1995 book “Deke! US Manned Space – From Mercury To The Shuttle”, he would speak about the incident in detail.