Project Blue Book was one of a series of systematic studies of
unidentified flying objects (UFOs) conducted by the
United States Air Force. It started in 1952, and it was the third study of its kind (the first two were projects
Sign (1947) and
Grudge (1949)). A termination order was given for the study in December 1969, and all activity under its auspices ceased in January 1970.