On January 7, 1948, Captain Thomas F. Mantell, an experienced 25-year-old pilot, crashed his F-51D Mustang and was killed while in pursuit of an Unidentified Flying Object (UFO) over Kentucky. The object had been observed by numerous witnesses on the ground, including military police and personnel at Godman Army Airfield at Fort Knox.1 Mantell's death during an interception attempt became one of the first and most sensational stories of the early UFO era, sparking widespread public speculation and official inquiry.2
The Pursuit
After multiple ground sightings of a large, circular, and metallic-looking object, Mantell was leading a flight of four National Guard fighters when he was diverted to investigate.3 He reported the object was "metallic and of tremendous size" and appeared to be climbing. Ignoring recommendations to level off, Mantell continued his pursuit above 25,000 feet without oxygen equipment, while his wingmen broke off.4 His last radio transmission was garbled, and his plane was later found crashed on a farm near Franklin, Kentucky.1
Investigation and Explanation
The U.S. Air Force's initial investigation suggested Mantell may have been chasing the planet Venus, but this was quickly challenged due to the object's apparent size and movement.2 The official explanation later concluded that Mantell had misidentified and was fatally pursuing a classified high-altitude Skyhook balloon, which was being used for cosmic ray research and was unknown to the public and most military personnel at the time.5 The Air Force concluded that he lost consciousness due to hypoxia (lack of oxygen) at high altitude, causing him to lose control of his aircraft.4