Project Sign Technical Report

February 1949 — US Air Force / Air Materiel Command

Overview

Project Sign was the first official US Air Force investigation into unidentified flying objects, established in late 1947 in direct response to the wave of flying saucer sightings that began with Kenneth Arnold's report in June 1947 and the Roswell incident in July 1947. The project was based at Wright-Patterson Air Force Base and tasked with determining whether UFOs posed a national security threat.

The Estimate of the Situation

The most significant product of Project Sign was a classified document known as the "Estimate of the Situation" — a top-secret assessment that concluded the most credible UFO sightings were likely extraterrestrial in origin. This document was reportedly sent to Air Force Chief of Staff General Hoyt Vandenberg, who rejected the conclusion as unsupported and ordered all copies destroyed.

Key Cases

Project Sign investigated several significant incidents, including the death of Captain Thomas Mantell on January 7, 1948, who died while pursuing a UFO in his P-51 Mustang over Kentucky, and the Chiles-Whitted encounter of July 24, 1948, in which two airline pilots observed a torpedo-shaped craft with glowing windows pass their aircraft at close range.

Legacy

Although Project Sign was reorganized into Project Grudge (which took a debunking approach), its original "Estimate of the Situation" remains one of the most important documents in UFO history — evidence that the Air Force's own investigators initially concluded that UFOs had an extraterrestrial explanation.