Believers and skeptics both agree that Captain Thomas Mantell was a real-life UFO victim. However, whether or not the UFO was as real as its prey is another story.

On the afternoon of January 7, 1948, the Kentucky Highway Patrol found itself inundated with reports of a flying saucer moving wildly to the west. The white, umbrella-shaped object of indeterminate size, seen from southern Ohio to central Tennessee, was rapidly changing speed and bearing in the clear blue sky. The Highway Patrol notified the military, which in turn decided to send the Air National Guard to investigate the reports.

Three P-51D Mustangs, led by Captain Mantell, arrived in the area of Fort Knox approximately an hour and a half after the first UFO sightings. Throughout the investigation, Mantell was in radio contact with the control tower at nearby Godman Air Force Base. The Mustangs quickly spotted the object and began ascending southwesterly at top speed in an attempt to get close enough to identify it. Mantell reported his observations to Godman:

Capt. Mantell: I am at 15,000 feet. I have the object in sight above and ahead of me, and it appears to be moving at about half my speed or approximately 180 miles per hour. I am going up to 20,000.

Godman AFB: Can you, uh, give us a description of the object? Over.

Capt. Mantell: It appears to be a metallic object or possibly reflection of sun from a metallic object, and it is of tremendous size.

At 23,000 feet, Mantell's wingmen dropped out of the chase due to lack of oxygen. Mantell, in his final communication, remained steadfast in his desire to "close in for a better look". By 3:15, his plane was lost to the National Guard. However, several civilian eyewitnesses on the ground saw Mantell's airplane level off, circle around, and then initiate a precipitous, spiraling dive. Somewhere around 15,000 feet, the aircraft exploded.

The severely damaged and half-buried wreckage of Mantell's P-51 was discovered after 5:00 on a farm near Franklin, Kentucky. The body of Mantell, still locked in the cockpit, was wearing a watch which had shattered at 3:18, presumably the moment of impact.

The Air Force's report determined that Mantell blacked out due to lack of oxygen around 25,000 feet. His plane had continued climbing to about 30,000 feet before going out of control. An aggressive pilot, Mantell had been determined to identify the threat at hand, and had paid the ultimate price. This was the height of the late 1940's UFO craze, and there was a sense of urgency about discovering the source of these mysterious objects.

Of course, the 1948 UFO wave also led to numerous, widely-believed, fictitious accounts of Mantell's demise. There were reports of a "death ray" fired from the object. Some claimed that Mantell's body was not found amongst the wreckage. Others said it was present – but full of bullets or highly radioactive. In time, these fanciful tales disappeared and the focus switched to the nature of Mantell's crafty eluder.

A Project Sign investigation, led by the esteemed Dr. J. Allen Hynek, famously concluded that the object was Venus, possibly coupled with airborne balloons. The public disregarded this report quickly. Venus at that time was not consistent with the brightness and locations of the sightings, and public records revealed no balloon activity. The controversial case and conclusion eventually tore apart Project Sign.

Today, Hynek is vindicated. As outlandish as it sounds, several of the reports can be directly attributed to the planet Venus. However, the balloon suggestion was his real triumph. There was indeed no public record of balloon activity over Kentucky on that day, but there was a major clandestine operation. A top secret (and immense) Skyhook balloon had been over the area. These balloons fit the descriptions given by most ground-based observers, as well as the reports of Mantell's wingmen. Skyhooks flew at 60,000 feet. This once controversial case is for all intents and purposes settled.

Anoxia, compounded by a mission's secrecy and a country's mania, is what killed Captain Thomas Mantell.