InvestigationProject SIGN (July 1947 – February 1949)

Project SIGN (originally given the cover name “Project Saucer” in early 1948) was the first formal U.S. Air Force investigation of unidentified aerial phenomena. It was opened at the Air Materiel Command Technical Intelligence Division at Wright Field, Dayton, Ohio, on 30 December 1947 by directive of USAF Commanding General Nathan F. Twining, in response to the post-24-June-1947 (Arnold) sighting wave. The first project officer was Capt. Robert R. Sneider; chief analyst Alfred C. Loedding; scientific consultant Dr. J. Allen Hynek (then Northwestern University Department of Astronomy, beginning his 22-year USAF UFO-investigation consultancy).

Project SIGN operated under the codename SIGN from December 1947 through February 1949. Its primary product was a Top Secret staff study, the “Estimate of the Situation,” drafted in summer 1948 by SIGN’s senior staff (Sneider, Loedding, and others), which surveyed the year’s accumulated sighting reports — including the Arnold sighting (June 1947), the Mantell incident (January 1948), and the Chiles-Whitted “rocket ship” sighting over Montgomery, Alabama (24 July 1948) — and reportedly concluded that the most reasonable explanation consistent with the witness corpus was that the objects were “interplanetary” in origin.

The Estimate was forwarded up the chain of command and reached USAF Chief of Staff Gen. Hoyt S. Vandenberg in late summer 1948. Vandenberg — formerly the second Director of Central Intelligence (1946–47) — rejected the Estimate’s conclusion on the grounds that the interplanetary hypothesis “lacked physical evidence.” He returned the document with instructions to declassify and destroy. No copy of the Estimate has ever surfaced in the public record; its existence is attested primarily by Capt. Edward J. Ruppelt’s 1956 memoir The Report on Unidentified Flying Objects (see also estimate-of-situation-1948).

Following Vandenberg’s rejection, Project SIGN was reorganized into the more skeptical Project GRUDGE in February 1949, under a posture that favored prosaic explanations and reduced the resources allocated to UFO investigation. The SIGN-to-GRUDGE transition is the canonical documentary instance of senior USAF leadership reversing a project-level interplanetary-hypothesis finding. SIGN’s final report, “Project Sign Final Report No. F-TR-2274-IA,” was issued in February 1949, with a conclusion substantially more skeptical than the rejected Estimate.

See also: blue-book; project-grudge-1949-1951; estimate-of-situation-1948.