The footage, slowed down for effect, was published by “Section 51”, a US-based conspiracy theory YouTube channel collecting footage of “unidentified flying objects”.
It shows a fighter shadowing a US jet as it comes into land, while a triangular object can clearly be seen beside a Navy helicopter.
Commenting on the video, many people believed the object was a TR-3B, a supposed anti-gravity spy plane vehicle some maintain the US air force is developing.
One amazed YouTube user wrote: “TR-3B. It really exists!”
Another offered a detailed explanation, writing: “I think it’s a TR-3B, the latest of the US’s black projects vehicles.
“This is the next generation of secret technology developed by the skunk works and other secret development programs.
“It is in any case not alien. It might have been developed with the use of reverse-engineered alien technology. But built on this planet.”
Others were not so convinced, with user Jim Hatch penning: “Pretty sure they wouldn’t leave it parked on the deck of an aircraft carrier, was it an alien spacecraft or some sort of secret technology?”
And others suggested the object was Photoshopped into the footage, joking about the triangle craft’s “stealth shadow”.
One said: “Nice CGI.”
Another sceptic said: “So tell me why a craft which can defy gravity and travel faster than anything known by mankind, which doesn’t use fossil fuel stands on the deck of an aircraft carrier?”
But there were some who were not sure what to think.
Matt Simon said: “The problem with today’s CGI is that it’s getting damn near impossible to know what is real and what is fake.
“Unless you’re right there to actually witness it with your own eyes, when you see a compelling video and wonder if it’s real or fake, sometimes all you can do is shake your head and shrug your shoulders.”
Eventually, ufoofinterest.org, which claims to “debunk hoaxes, conspiracies and misinformation”, rubbished the UFO claims.
The group tweeted a video which showed the original US Navy training footage with no UFO in sight, proving it had been doctored.
They said: “Triangle shaped UFO spotted on US Aircraft Carrier in the Mediterranean Sea?
“It’s interesting to check out which sources the hoax promoter and CGI artist SECTION 51 used to fabricate his latest video.
“Here’s a source without that fake UFO.”