Top Secret assessment written by the staff of Project Sign in the late summer of 1948, which is reported to have concluded that the objects were interplanetary. It went up the chain to the Air Force Chief of Staff, Hoyt Vandenberg, who rejected it for want of proof, and the copies were destroyed.
The evidential position
No copy has ever surfaced. Its existence rests on the testimony of people who say they read it, most importantly Edward Ruppelt, who ran Project Blue Book and described the document in his 1956 book, and on the abrupt change of direction at Sign, which was renamed Project Grudge within months and reoriented toward explanation rather than assessment.
Why it carries weight anyway
It is the earliest instance of the pattern the modern record keeps producing: an internal assessment that reaches a conclusion the institution will not carry, followed by a reorganisation. Ross Coulthart uses it in In Plain Sight as the hinge of the argument that official dismissal was a policy rather than a finding, and it sits directly beside the Twining Memo 1947, which is a real document saying the phenomenon is something real and not visionary or fictitious.
Connections
Project Sign · Project Grudge · Project Blue Book · Twining Memo 1947 · Nathan F. Twining · In Plain Sight · Ross Coulthart · Triple Coverup