Project Sign was the first U.S. Air Force investigation of UFOs and lasted from January 1948 to April 1949. Based at Wright-Patterson AFB, Dayton, OH, it collected several hundred sighting reports from government and
nongovernment sources, and claimed to explain most of them. Due to its unwillingness to accept UFO reports not sent directly to it, the Project Sign files include only a few dozen reports from 1947, while newspapers received more than
1 ,500 reports in just two weeks.