Interestingly enough, the Foo Fighter reports were explained by the Germans as American devices, and by the Americans as German machines. UFO sightings made by military personnel reached a peak in the mid-1940s, and the attention of the Air Force reached a new level. Classified orders gave instruction that these sightings be sent to the Technical Intelligence Division of the Air Force Materiel Command at Wright-Patterson Air Field.
The Air Force became a separate branch of the military in late summer of 1947, and the Air Intelligence at the Pentagon requested a report from the Air Materiel Command for information on Unidentified Flying Objects. A conference was called by Lt. General Nathan F. Twining, with personnel from several different branches within the service to discuss the UFO mystery.
This "think tank" produced a number of definitive conclusions: The UFO phenomena is real, and not visionary or fictitious, there are disc-shaped objects the size of airplanes flying in our skies, some of the sightings could be caused by natural phenomena, the operating characteristics of the unknown objects was extraordinary, such as rates of climb, maneuverability, and evasiveness.
Also given was a "common description." These objects were seen as metallic or light reflecting, they give no contrail, they were usually circular or elliptical in shape, flat on the bottom, and domed on top. It was not uncommon for the objects to be seen in groups of anywhere from three to nine.
Also, the objects made no sound, except for some reports of "rumbling" sounds. Any "private" enterprise of these objects was nearly impossible, due to the immense cost involved. The possibility that a foreign government possessed this technology could not be ruled out, however.
After all was said and done, on December 30, 1947, Major General L.C. Craigie, Director of Research and Development, issued an official order establishing "Project Sign." This project was also often referred to as "Project Saucer."
The main objective of Sign was... to collect, collate, evaluate and distribute to interested government agencies and contractors all information concerning sightings and phenomena in the atmosphere which can be construed to be of concern to the national security.
There were differing reactions to reports of UFOs being explained as extraterrestrial in origin, and some parts of reports were expunged, causing personal differences to inflame the project. Shortly thereafter Sign would officially be changed to Project Grudge.