Unlike the WWII ff's these things could show up on ground-based and airborne radar and apparently could also accelerate from the speed of an F-82 - and maybe F-94 - to "thousands of miles an hour" almost instantly. Dad said that everyone would be communicating relatively routinely until the thing would zip off, then the pilot or r/o would blurt out an expletive and/or excitedly try and describe the speed at which it was now traveling.
He rather liked reminiscing about odd stuff like that... his talking to pilots of shot-up B-29s trying to get back to Kadena, not so much.
My brother flew F-94 fighter-interceptors during the Korean war, stationed in Japan. He and his squadron had quite an experience chasing a UFO.
When it was written up in Stars and Stripes, he sent me the article. I wish now that I had saved it !