You know a UFO has earned its "unidentified" status when cockpit transcripts from elite Navy fighter jets include this frantic pilot exclamation: "Holy s___, what is that?"

When Luis Elizondo ran a small team at the U.S. Department of Defense investigating military-based reports of unidentified aerial phenomena (UAP), he heard numerous such accounts—by some of the most highly trained aeronautic experts in the military. They describe objects that appeared to be intelligently controlled, possessing aerodynamic capabilities that far surpass any currently known aircraft technology.

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Now pursuing his investigations as part of To the Stars Academy of Arts & Sciences, Elizondo is an integral part of the investigative team featured on HISTORY's “Unidentified: Inside America’s UFO Investigation," where they have continued to gather eyewitness accounts like these:

"It's white. It has no wings. It has no rotors."

"It didn't fly like an aircraft. It was so unpredictable—high g, rapid velocity, rapid acceleration."

"I didn't see a trail."

"It was going 70-plus knots underwater."

Those reports—from Navy fighter pilots, radar operators and other witnesses from the USS Nimitz aircraft carrier strike group incident from November 2004—were among a handful of shocking encounters the Unidentified team explored. When Elizondo ran the Defense Department initiative, called the Advanced Aerospace Threat Identification Program, or AATIP, he compiled a list of extraordinary, logic-defying capabilities most commonly associated with unidentified aerial phenomena sightings. He calls those traits the “five observables”:

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1) Anti-gravity lift

Unlike any known aircraft, these objects have been sighted overcoming the earth’s gravity with no visible means of propulsion. They also lack any flight surfaces, such as wings. In the Nimitz incident, witnesses describe the crafts as tubular, shaped like a Tic Tac candy.

2) Sudden and instantaneous acceleration

The objects may accelerate or change direction so quickly that no human pilot could survive the g-forces—they would be crushed. In the Nimitz incident, radar operators say they tracked one of the UFOs as it dropped from the sky at more than 30 times the speed of sound. Black Aces squadron commander David Fravor, the Nimitz-based fighter pilot who was sent to intercept one of the objects, likened its rapid side-to-side movements, later captured on infrared video, to that of a ping-pong ball. Radar operators on the USS Princeton, part of the Nimitz carrier group, tracked the object accelerating from a standing position to traveling 60 miles in a minute—an astounding 3,600 miles an hour. According to manufacturer Boeing, the F/A 18 Super Hornet fighter jet typically currently reaches a maximum speed of Mach 1.6, or about 1,200 miles an hour.

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3) Hypersonic velocities without signatures

If an aircraft travels faster than the speed of sound, it typically leaves "signatures," like vapor trails and sonic booms. Many UFO accounts note the lack of such evidence.

4) Low observability, or cloaking

Even when objects are observed, getting a clear and detailed view of them—either through pilot sightings, radar or other means—remains difficult. Witnesses generally only see the glow or haze around them.

5) Trans-medium travel

Some UAP have been seen moving easily in and between different environments, such as space, the earth’s atmosphere and even water. In the Nimitz incident, witnesses described a UFO hovering over a churning "disturbance" just under the ocean's otherwise calm surface, leading to speculation that another craft had entered the water. USS Princeton radar operator Gary Vorhees later confirmed from a Navy sonar operator in the area that day that a craft was moving faster than 70 knots, roughly two times the speed of nuclear subs.

No one has yet gotten close to crafts that display these traits, so their origins are still unknown. Are they a super-top-secret U.S. defense project? Do they hail from Russia? China? Or from even further afield? The only thing we do know is that their capabilities exceed any technologies currently in the U.S. arsenal.

READ MORE: Interactive Map: UFO Sightings Taken Seriously by the U.S. Government.

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