THESE are the mysterious aircraft that many believe hold the answer to one of the world's great alien conspiracies.

The unmarked white and red Boeing 737s appear like any other at first sight.

Lined up at Las Vegas' McCarran International Airport, several of the giant jets use their own private terminal.

But they are not used by the public and only serve one destination - Area 51.

4 The mysterious jets are lined up beside a private terminal at the McCarran International Airport near Las Vegas Credit: Alamy

4 The unmarked 737 jets only fly between the airport and the notoriously secretive Area 51 - where many believe there is evidence of aliens Credit: Wikipedia

Extra terrestrial theorists believe the top-secret military base - hidden away in the Nevada desert - contains the remains of an alien aircraft that crashed in the 1950s.

The area was bought up by the US military in 1955 and its existence was only acknowledged for the first time in 2005.

It is believed to be the testing site for top-secret cutting-edge military technology.

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The jets are run by the United States Air Force and even have their own mysterious call sign - Janet Airlines.

Nobody who flies on the planes is allowed to reveal where they are going or what their job is.

Operating from a private terminal at the Vegas airport, they only fly to and from Area 51.

But an extra-terrestrial expert who used to investigate UFOs for the British Ministry of Defence believes there is little to the rumours.

Nick Pope told the Mail: "Area 51 exists - it's part of a military testing range in Nevada - and because of the remote and sparsely-populated location, it's where various secret prototype aircraft and drones are developed and test flown.

4 The top secret military base was bought up by the US government in 1955 and was only acknowledged for the first time in 2005 Credit: Alamy

4 Some conspiracy theorists believe it is the site of an alien crash landing in the 50s Credit: Alamy

"The UFO and conspiracy theory community think it's the place where crashed UFOs are kept and where the US military are trying to back-engineer this alien technology.

"And even Hillary Clinton has said that if she's elected President she'll look into the claims.

"Sadly, despite the rumours, I've seen no evidence that we've recovered any extraterrestrial technology.

"Having been name-checked in movies like Independence Day, Area 51 has become part of pop culture and the secret is out, so if there ever was alien technology at Area 51, I suspect it's been moved to a location we've never heard of."

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