Air Materiel Command Report on Unidentified Flying Objects, 1947–1948 — Department of War File
This file is a collection of U.S. Government memoranda and correspondence relating to “Project Sign,” a 1948 U.S. Air Force program to investigate reports of high-performance airborne objects. The documents characterize some of these reports as being consistent with “real” objects rather than…
Incident Overview
In 1947–1948, in an undisclosed location, the Department of War preserved a documentary record that was declassified and published on August 7, 2026 as part of the fifth tranche of the Department of War’s Presidential Unsealing and Reporting System for UAP Encounters (PURSUE).
What the government released
This file is a collection of U.S. Government memoranda and correspondence relating to “Project Sign,” a 1948 U.S. Air Force program to investigate reports of high-performance airborne objects. The documents characterize some of these reports as being consistent with “real” objects rather than fabrications or resulting from perceptual errors. The U.S. Air Force cites the reported characteristics of the phenomena, e.g., high speed and maneuverability, as exceeding known performance envelopes of U.S. military aircraft and thereby presenting a potential national security threat, if validated. This potential threat prompted the Air Force to call on the Air Materiel Command (AMC), the Service’s Major Command for logistics and procurement from 1946 to 1961, to gather further evidence to assess the validity of the reports. The Air Force emphasized that there was an “imperative need” for such evidence to enable appropriate countermeasures. The stated urgency of this request reflects the strategic environment of the early Cold War, a period characterized by heightened national defense concerns amid rapid global advancements in aerospace design and development. In framing the call for an investigation, the Air Force noted that sustained public interest and persistent inquiries from the press may eventually require an official statement in response.
AMC’s investigation found that observers were generally not mistaken when reporting that they had seen an airborne object, but that their characterizations of those objects as unusual was likely a reflection of the “limits of their personal experience.” It identified “a great many” of the objects reported with a rounded appearance as “weather or upper air scientific balloons of some type.” It also identified several cases in which the reported objects were most likely celestial phenomena, such as Venus. AMC found that a small number of reports lacked a “reasonable everyday explanation,” but that “so far, no physical evidence of the existence of the unidentified sightings has been obtained.” AMC expressly considered whether the phenomena may have been “vehicles from another planet,” but found no evidence supporting such an origin. Ultimately, AMC found that “there is as yet no conclusive proof that unidentified flying objects, other than those which are known to be balloons, are real aircraft.” In light of these findings, AMC recommended that the Department of War should avoid publicly commenting on the subject of “flying discs.” Responding to the Air Force’s anticipated concerns regarding public interest in the subject, AMC recommended that the Department should reply in terms that minimize the investigation’s inconclusive findings, focusing on positive determinations in cases assessed to be weather balloons and celestial phenomena.
The case in this archive
This document is a primary source for the Project Sign progress report, written up here at length from the contemporary record. The file and the case history are worth reading against each other: the document is narrower and more cautious than the account that grew up around it, which is usually the point.
Status of the case
This is an archival document, and it should be read as one. It records what a particular office believed, or was willing to commit to paper, on the day it was written — not a present-day finding. The mid-century investigations worked from witness testimony, sparse instrumentation, and the strategic anxieties of the early Cold War, and the great majority of the sightings they catalogued were eventually attributed to aircraft, balloons, astronomical objects, and misidentification. The All-domain Anomaly Resolution Office has made no modern determination about the incidents described here, and the document’s release is not an endorsement of the conclusions inside it. Its value is as evidence of how the United States government investigated the question, and of what it chose to keep.