s category called
unknown. This means that the observer was not affected by any
determinable psychological quirks and that after exhaustive
investigation the object that was reported could not be identified.
To be classed as an unknown, a UFO report also had to be "good,"
meaning that it had to come from a competent observer and had to
contain a reasonable amount of data.

Reports are often seen in the newspapers that say: "Mrs. Henry
Jones, of 5464 South Elm, said that 10:00A.M. she was shaking her
dust mop out of the bedroom window when she saw a flying saucer"; or
"Henry Armstrong was driving between Grundy Center and Rienbeck last
night when he saw a light. Henry thinks it was a flying saucer." This
is not a good UFO report.

This type of UFO report, if it was received by Project Blue Book,
was stamped "Insufficient Data for Evaluation" and dropped into the
dead file, where it became a mere statistic.

Next to the "Insufficient Data" file was a file marked "C.P." This
meant crackpot. Into this file went all reports from people who had
talked with flying saucer crews, who had inspected flying saucers
that had landed in the United States, who had ridden in flying
saucers, or who were members of flying saucer crews. By Project Blue
Book standards, these were not "good" UFO reports either.

But here is a "good" UFO report with an "unknown" conclusion:

On July 24, 1952, two Air Force colonels, flying a B-25, took off
from Hamilton Air Force Base, near San Francisco, for Colorado
Springs, Colorado. The day was clear, not a cloud in the sky.

The colonels had crossed the Sierra Nevada between Sacramento and
Reno and were flying east at 11,000 feet on "Green 3," the aerial
highway to Salt Lake City. At 3:40P.M. they were over the Carson Sink
area of Nevada, when one of the colonels noticed three objects ahead
of them and a little to their right. The objects looked like three F-
86's flying a tight V formation. If they were F-86's they should have
been lower, according to civil air regulations, but on a clear day
some pilots don't watch their altitude too closely.

In a matter of seconds the three aircraft were close enough to the B-
25 to be clearly seen. They were not F-86's. They were three bright
silver, delta wing craft with no tails and no pilot's canopies. The
only thing that broke the sharply defined, clean upper surface of the
triangular wing was a definite ridge that ran from the nose to the
tail.

In a