A need for as much additional information as possible about these craft, their performance characteristics and their purpose led to the undertaking known as U.S. Air Force project SIGN in December, 1947… SIGN evolved into project GRUDGE in December, 1948. The operation is currently being conducted under the code name BLUE BOOK, with liason [sic] maintained through the Air Force officer who is head of the project.”
(Eisenhower briefing page 005)
Following the Arnold incident, the Air Force was given the responsibility of investigating UFO reports from the United States, first as Project Sign (also called Saucer), then Grudge, and finally Blue Book. Usually understaffed and underfunded, the Air Force program functioned more like a public relations office than a scientific investigation, according to the late astronomer J Allen Hynek.
(paranetinfo.com – site now defunct)
Project Blue Book terminated.