Project Sign: The U.S. Air Force's first UFO investigation that left 20 percent of cases a mystery

In September 1947, the U.S. Air Force received numerous reports of mysterious objects in the sky. These reports left the public on edge. In response, the government launched an investigation called Project Sign. Since then, the government has received many of such reports, and even today, these sightings are shared by the Pentagon.

Here’s a look at how the investigation into the mysterious UFO sightings really began.

By early 1948, the Project Sign team wanted an astronomer who could spot sightings caused by planets or meteors. At that time, J. Allen Hynek was the director of Ohio State University’s McMillin Observatory. His wartime work on defense technology, including the first radio-controlled fuse, meant that he already had a high security clearance.

When Air Force visitors asked him to consult, he agreed. “I had scarcely heard of UFOs in 1948 and, like every other scientist I knew, assumed that they were nonsense,” he recalled.

Project Sign ran for a year and reviewed a total of 237 cases. In Hynek’s final report, he shared that about 32 percent of those reports traced back to astronomical causes. About 35 percent had other explanations, like balloons, rockets, flares or birds. 

But the other 13 percent lacked enough evidence. That left 20 percent with some evidence but no explanation. The Air Force was reluctant to use the phrase “unidentified flying object,” so it simply labeled them “unidentified.”

Hynek joined Project Blue Book in 1952. Most of the work was paperwork, but puzzling cases sometimes sent him into the field. There, he found that the people reporting UFOs seemed quite normal. “The witnesses I interviewed could have been lying, could have been insane or could have been hallucinating collectively—but I do not think so,” he recalled in his 1977 book.

In 1972, Hynek published his book titled The UFO Experience, in which he introduced his “Close Encounters” categories. The first kind means seeing a UFO up close, with details visible. In the second, the UFO leaves a physical mark, like scorched trees or car engines that suddenly die. In the third, witnesses report seeing occupants. 

Hynek never solved the mystery of UFOs. And reports of these strange sightings still continue to surface, including in the Pentagon’s recent release of UFO files. To this day, what these sightings actually represent remains unresolved.