The top-secret US Airforce facility hidden away in the Nevada desert is so classified that it was only in 2013 that the US Government openly admitted it existed.
And, last year Hillary Clinton vowed to send in a task force to find out just what goes on inside it if she made it to the White House as part of her election campaign.
Theories about what Area 51 is used for range from the development of classified aircraft to a storage facility for recovered UFOs and alien body parts after alleged flying saucer crashes.
Armed private security guards are authorised to use “lethal force” on anyone foolish enough to enter the site unannounced.
Last year, Express.co.uk ran a poll asking readers if they believed evidence of alien visitations of Earth was being hidden in Area 51.
There were 7,139 votes, and a remarkable 66 percent thought there was an alien cover up under way inside Area 51.
But, industry insider Andre Milne, founder of defence technology firm Unicorn Aerospace, which describes itself as “the world’s leading developer of advanced navigation technology”, claims this is not the case.
He says one of Area 51’s main purposes is to test Russian warplanes to ensure the US stays one step ahead of its Cold War rival.
Mr Milne claimed the US Airforce (USAF) uses Area 51 to study Russian fighter jets – something that used to be done by The 4477th Test and Evaluation Squadron at various locations until it was formally disbanded in July 1990.
He said: “An operational priority of the USAF is to fully understand the maximum endurance combat threshold of any potential adversaries primary front line military fighter aircraft.
“Following the official disbandment of The 4477th Test & Evaluation Squadron that was tasked with actively studying Russian fighter jets, Area 51 is now the unofficially designated base that does the exact same work as The 4477th.
“Hopefully this helps in quashing the nonsensical myth that Area 51 is intertwined with some fictitious alien technology conspiracy.
“Area 51 is a highly secured aerospace facility tasked with a wide variety of objectives to ensure the United States maintains a cutting edge of tactical air superiority against any potential threats.”
Last month Expresss.co.uk revealed pictures taken by a photographer of a mock dog fight between a US F-16 and a Russian Sukhoi SU-27 taking place in the skies above Area 51, before the fighters returned to base..
Mr Milne said that was an example of the work at Area 51 he has told of being underway.
He has previously told how so-called “Black Projects” are also underway inside Area 51.
Black Projects is a conspiracy theory name for the top-secret development of new experimental military aircraft.
Mr Milne says this is also ongoing at Area 51.
He said: “Area 51 is a very well secured US Air Force base that is mandated to test and evaluate the performance of experimental and or classified US military aircraft.
“The whole alien question being run out of Area 51 is complete nonsense.”
According to its website, Unicorn Aerospace is “committed to development of advanced aerospace technologies in order to maximise revenue stream growth potential into the respective markets of the private commercial and public military sectors.”.
Express.co.uk has contacted the United States Department of Defense for comment.