Mantell, a Kentucky Air National Guard pilot, died in the crash of his P-51 Mustang fighter, after being sent in pursuit of an unidentified flying object (UFO).
The event was among the most publicized early UFO incidents.
Later investigation by the United States Air Force's Project Blue Book indicated that Mantell may have died chasing a Skyhook balloon, which in 1948 was a top-secret project that Mantell would not have known about.
Mantell pursued the object in a steep climb, and disregarded suggestions to level his altitude.
At high altitude he blacked out from a lack of oxygen, his plane went into a downward spiral, and crashed.
In 1956, Air Force Captain Edward J.
Ruppelt (the first head of Project Blue Book) wrote that the Mantell crash was one of three "classic" UFO cases in 1948 that would help to define the UFO phenomenon in the public mind, and would help convince some Air Force intelligence specialists that UFOs were a "real", physical phenomenon.
The other two "classic" sightings in 1948 were the Chiles-Whitted UFO encounter and the Gorman dogfight.Historian David M.
Jacobs argues the Mantell case marked a sharp shift in both public and governmental perceptions of UFOs.
Previously, the news media often treated UFO reports with a whimsical or glib attitude reserved for “silly season news”.
Following Mantell's death, however, Jacobs notes "the fact that a person had died in an encounter with an alleged flying saucer dramatically increased public concern about the phenomenon.
Now a dramatic new prospect entered thought about UFOs: they might be not only extraterrestrial but potentially hostile as well."