It all began in 1947. Lt. General Nathan Twining, the commander of Air Materiel Command, sent a secret memo on “Flying Discs” to the commanding general of the Army Air Forces at the Pentagon. Twining stated that “the phenomenon reported is something real and not visionary or fictitious.” The silent, disc-like objects demonstrated “extreme rates of climb, maneuverability (particularly in roll), and motion which must be considered evasive when sighted or contacted by friendly aircraft and radar.”
A new project, code-named “Sign,” based at Wright Field (now Wright-Patterson Air Force Base) outside Dayton, Ohio, was given the mandate to collect U.F.O. reports and assess whether the phenomenon was a threat to national security. With Russia ruled out as the source, the staff wrote a top secret “Estimate of the Situation,” concluding that, based on the evidence, U.F.O.s most likely had an interplanetary origin.
According to government officials at the time, the estimate was rejected by General Hoyt Vandenberg, the Air Force chief of staff. From then on, the proponents of the off-planet hypothesis lost ground, with Vandenberg and others insisting that conventional explanations be found.
Project Sign eventually evolved into Project Blue Book, with the aim of convincing the public that flying saucers could be explained.
Yet behind the scenes, authorities grappled with something sobering: Well-documented U.F.O. encounters involved multiple trained observers, radar data, photographs, marks on the ground and physical effects on airplanes.
In 1952, Major General John Samford, the Air Force director of intelligence, briefed the F.B.I., saying it was “not entirely impossible that the objects sighted may possibly be ships from another planet such as Mars,” according to government documents. Air Intelligence had largely ruled out an earthly source, the F.B.I. memo reported.