Ever since it came into the public eye in 1989, Area 51 has been a source of conspiracy, with many questioning its purpose and whether the US government is hiding something from the public behind its heavily guarded barbed wire fence. The site's existence was officially acknowledged by the CIA only in 2013.

Now, the 400-page report by the CIA has resurfaced and is catching the attention of many for the first time as it's being shared on the popular social media site X. The report highlights many of the base’s activities pre-1974, outlining how secret U-2 spy plane testing was the explanation for many potential UFO sightings. The report stated: "High-altitude testing of the U-2 soon led to an unexpected side effect - a tremendous increase in reports of unidentified flying objects (UFOs).

"Once U-2s started flying at altitudes above 60,000 feet, air-traffic controllers began receiving increasing numbers of UFO reports.

"At times, when a U-2 pilot made a turn, the sunlight reflecting off the U-2’s silver wings would cause a series of glints or flashes. This caused airliner pilots to report seeing a bright object high above them."

The base was constructed in July 1955, and contained just a runway, housing, water wells and a small amount of hangar and shop space.

The following month, the CIA began there project AQUATONE, a programme to develop the Lockheed U-2 strategic reconnaissance aircraft.

The aircraft was designed to survey the Soviet Union from a great distance, and to aid in building intelligence during the Cold War.

Following these test flights, the base began the OXCART programme in 1960, which developed the A-12 reconnaissance plane.

This new aircraft was able to undertake missions where speed and stealth were pivotal, with it being used for five years to fly over areas deemed politically sensitive.

"In early 1962, CIA officials became concerned about the possibility that the Soviet Union might learn about the OXCART program through overhead reconnaissance," the document went on to say.

To test this, they had Area 51 itself "photographed by a U-2 and later by a CORONA reconnaissance satellite".

However, astronauts on America’s first space station also photographed the site.

The Skylab astronauts inadvertently photographed the Groom Lake test site despite specific instructions not to do so.

The report itself was obtained through a Freedom of Information Act request made in 2005, yet many have been critical of it.

"The notion that the U-2 explains most sightings at that time is utter rot and baloney," self-proclaimed Ufologist Stanton Friedman said in 2013.

"Can the U-2 sit still in the sky? Make right-angle turns in the middle of the sky? Take off from nothing?"