Disk Over Los Alamos
My uncle worked on the Manhattan Project at Los Alamos during the 1940s and told me of this incident shortly before he died several years ago.
One day, a bright silvery disk was observed in the sky hovering over the facility and a plane was immediately dispatched from Kirtland Field to intercept and identify the object.
As the plane approached, the disk ascended upward out of its range.
A second larger plane with a higher operational ceiling was then sent up to continue the pursuit, and again the disk ascended upward until it disappeared.
Apparently, this incident was witnessed by a number of the facility staff.