Area-51's ultra-top secret cover was almost blown by one photograph Those with overactive imaginations contest it is where the United States government keeps live extraterrestrials, their spaceships and also where NASA concocted their fake moon landings. But Groom Lake, or as it is better known - Area 51 - is the site of the U.S. Air Force's top-secret aircraft development and according to the CIA no other place on Earth is as sensitive. However, new declassified documents outline how rookie astronauts aboard Skylab in 1974 inadvertently photographed the Nevada site and caused a huge national security debate that almost led to the acknowledgement of Area-51 almost 40 years before the CIA officially did. Image that caused a fuss: Photograph of the secret facility at Groom Lake taken by the Skylab 4 astronauts Astronauts Gerald Carr, Edward Gibson and William Pogue were the third and last Skylab crew launched into space on November 16th, 1973. Their mission was a qualified success and as part of it they took photographs of the Earth from space - including those of the ultra-high security Area 51. However, when they splashed down 280 kilometers southwest of San Diego on February 4th the first signs of a problem arose. Under the terms of a long-standing agreement between NASA and the US intelligence community all images taken from space were to be examined by the National Photographic Interpretation Center in Washington D.C. Compromising photographers: A photograph of the Skylab Space Station taken by a crew of astronauts on their way home Do not enter: Signs outside Groom Lake - Area 51 - show how tight security is around the top secret facility They discovered pictures of Groom Lake and the panic caused by this traveled as high as the CIA Director, William Colby. On April 19th, 1974, Colby sent a memo to undisclosed colleagues with equivalent security clearance stating, 'The issue arises from the fact that the recent Skylab mission inadvertently photographed the airfield at Groom Lake. 'There were specific instructions not to do this,' the memo stated, and Groom 'was the only location which had such an instruction.' This one memo confirms that the CIA considered Area 51 the only place on Earth too sensitive to be photographed from space. This was because although it was tacitly known amongst intelligence personnel that aircraft such as the U-2 spy plane and A-12 - the precursor to the legendary SR-71 Blackbird - were being tested, 'there were a lot more things going on at Groom than that'. Pushing boundaries: One of the aircraft tested at Groom Lake - Area 51 - was the A-12 - which was the precursor to the iconic SR71 Blackbird spy craft Test: This is the Have Blue - the test aircraft that led to the F117 Nighthawk the stealth fighter extensively tested at Area 51 by the U.S Air Force Now this of course was not alien spacecraft, but early drone technology and captured Russian aircraft. The photograph caused such a stir within the intelligence community that the issue became a hot potato that was thrown around the Pentagon, the USAF, NASA, the Justice Department and the CIA. 'This photo has been going through an interagency reviewing process aimed at a decision on how it should be handled,' one unnamed CIA source revealed according to The Space Review. There is no agreement. Department of Defense elements all believe it should be withheld from public release. NASA, and to a large degree State (department), has taken the position that it should be released. The mistake of the Skylab astronauts had inadvertently created tensions between civilian U.S. government agencies and those of the military. Colby expressed some doubts about the need to protect the image, since the Soviet Union had it from their satellites anyway. He further asked, 'If exposed, don't we just say classified USAF [U.S. Air Force] work is done there?' The CIA's declassified map of Groom Lake/Area 51 released in July - the first time the CIA admitted the facility in fact existed While NASA struggled with the decision, as a civilian agency they would have been keen for foreign governments not to assume that they engaged in spying or concealed their activities. 'There are some complicated precedents which, in fairness, should be reviewed before a final decision,' admitted the CIA source. Some of these included, 'A question of whether anything photographed in the United States can be classified if the platform is unclassified; Such complex issues in the UN concerning United States policies toward imagery from space" and 'the question of whether the photograph can be withheld without leaking.' As it transpired, the photo was withheld and never leaked and has only been released because the CIA decided to declassify documents. Spy Plane: The U-2 aircraft was one of the projects that initially placed the Groom Lake facility out of bounds for anyone without the highest security clearance Indeed, only in July 2013, following a FOIA request filed in 2005, the Central Intelligence Agency publicly acknowledged the existence of the base for the first time by declassifying documents detailing the history and purpose of Area 51. More than 60 declassified documents on the base were posted online last month by the National Security Archive in October. They reveal the U.S. governments desire to developed stealth aircraft such as the F117 and testing newly acquired Soviet Mig Fighter jets to assess their strengths and vulnerabilities. To dive into the Area 51 files, go to the National Security Archive's website: http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB443/