Project Blue Book Case #645. On February 25, 1950, an unidentified object was observed over Los Alamos, New Mexico — the nuclear weapons design laboratory. This was the earliest of multiple Blue Book unknowns from Los Alamos, occurring during the peak of the mysterious "green fireball" phenomenon that had alarmed scientists and military intelligence since late 1948.
Lincoln La Paz's investigation of the green fireballs was ongoing, and Project Twinkle was being organized to deploy observation equipment in the New Mexico corridor. The February 1950 Los Alamos sighting contributed to the sense of urgency driving these efforts.
Los Alamos in early 1950 was working toward the hydrogen bomb — President Truman had ordered a crash program to develop thermonuclear weapons just weeks earlier on January 31. Security concerns at the laboratory were at maximum intensity.
The case was classified "Unknown."