Project Sign — USAF First Official UAP Investigation

Project Sign was established by the US Army Air Forces on January 22, 1948, at Wright-Patterson AFB under the Air Technical Intelligence Center (ATIC). It was the first formal government UAP investigation program in US history. Project Sign analysts collected and evaluated incident reports from military personnel. In late 1948, the project's senior analysts produced a classified document known as the 'Estimate of the Situation' — an internal assessment concluding that the accumulated evidence most strongly supported an interplanetary origin for the best-documented UAP cases. The Estimate was forwarded up the chain of command to Air Force Chief of Staff General Hoyt S. Vandenberg. Vandenberg rejected the estimate, stating that the evidence was insufficient to support such a conclusion, and ordered all copies destroyed. Most copies were burned. Project Sign was reorganized and renamed Project Grudge in February 1949, with a new directive to debunk UAP reports rather than investigate them objectively. Captain Edward Ruppelt, who later headed Project Blue Book, noted in his memoir that Vandenberg's destruction of the Estimate of the Situation was a pivotal moment that shaped the USAF's officially dismissive posture toward UAP for the following two decades. A few surviving copies of the Estimate were discovered in 1969. Project Sign's case files are preserved at NARA as part of the Project Blue Book records.