Project Sign · UFOCosmos

The first official US Air Force investigation into flying saucers, established in 1947 following the Kenneth Arnold sighting and the Roswell incident. Sign concluded that some UFOs were real and possibly interplanetary in origin — a conclusion that was classified and the project was terminated.

Project Sign was established in December 1947 at Wright-Patterson Air Force Base under the command of Air Materiel Command. It was the first systematic government effort to investigate UFO reports following the Arnold sighting in June 1947 and the Roswell incident in July 1947. Sign investigators collected over 240 incident reports in its first year of operation. The project produced a classified document known as the "Estimate of the Situation," which concluded that UFOs were real aerial phenomena of possible interplanetary origin. The document was submitted to Air Force Chief of Staff General Hoyt Vandenberg, who rejected its conclusions and ordered it destroyed. Project Sign was renamed Project Grudge in 1949, which took a more dismissive stance toward UFO reports. The existence of the Estimate of the Situation remained classified and was only confirmed decades later by personnel who had worked on the project.