This description is second hand from my father.
He was a radar operator at Brunswick Navy Air Station from 1954 to 1958.
The guys that were on watch called everyone over.
They said we have been watching this for a few minutes.
And it wasn't declared, so they tracked it.
It went level for quite a distance then it flew off the radar.
The radar at the time went across for a distance.
The other Doppler, the best at the time, went from up to down.
Up it maxed out at 150,000.
He said they watched the aircraft move across and then it went straight up and up, right off the radar.
I asked him if it could have been a missile he said they didn't have any at the time.