CLASSIFIED!
AREA 51 has hit headlines again this week after a prank Facebook page encouraging alien hunters to storm the base en masse garnered more than 1.5million confirmed attendees.
The aim is to uncover whatever secrets are hidden there – but Area 51 is just a drop in the ocean when it comes to mysterious US bases.
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Dozens of secretive facilities are dotted across the globe, and we've put together some of the strangest below.
Area 6 – Nevada, USA
This top secret airbase was spotted in the Nevada desert on Google Earth in 2016.
The site is roughly 12 miles northeast of Area 51 and is part of the Nevada National Security Site, where 1,000 nuclear tests were carried out between 1945 and 1995.
Six nuclear tests and four detonations have been completed at Area 6, according to the US Department of Energy.
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The mysterious airbase has a 5,000ft runway that it's believed is used by federal agencies to carry out aircraft tests.
Area 6 is also believed be used to test Predator and Reaper drones.
The site was built in the 1950s for £7.7million but the lengthy runway seen in the Google Earth images was added in 2005.
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Fort Meade - Maryland, USA
Fort Meade is the headquarters of the mysterious National Surveillance Agency.
The NSA is tasked with surveillance and code-breaking, and its operations are shrouded in secrecy.
Unsurprisingly, Fort Meade has 24-hour security and its windows are mirrored to block out snoopers.
Whistleblower Edward Snowden leaked a series of documents in 2013 that proved the NSA was spying on American citizens.
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Pine Gap – Australia
Pine Gap is a top secret military compound located deep in the Australian Outback.
It's a joint venture between the Aussie and US governments and has been described as "Australia's Area 51".
Founded in 1970, the base was built at the height of the Cold War, with 400 American families flying to Australia to settle in nearby Alice Springs.
We don't know too much about the base, but the famed Edward Snowden WikiLeaks leak in 2013 lifted the lid on it a little.
Pine Gap is a satellite surveillance base and is involved in espionage operations.
The US National Surveillance Agency (NSA) uses the facility for the global interception and collection of internet and telephone communications.
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Diego Garcia - Indian Ocean
This tiny atoll has been a British Indian Ocean Territory since 1965.
In the 1970s, its 1,000 inhabitants were turfed out to make way for a joint US/UK military base.
Rumours have long circulated of a US prison camp on the tiny atoll in the Indian Ocean. Washington insists no such facility exists.
What is Area 51? The top secret US air base steeped in extra-terrestrial intrigue
AREA 51 is a highly classified US air base in the remote Nevada desert.
It is officially known as Homey Airport, but gained its now famous name from CIA documents that referred to it by the codename Area 51.
The exact purpose of the air base is not known publicly, and the area is heavily restricted.
Trespassers can face huge fines and lengthy prison sentences for setting foot in the zone.
Purchased by the US government in 1955, evidence suggests the site is used as a testing area for experimental aircraft and weapons.
But the secrecy surrounding it has led conspiracy theorists to suggest the area is holding extra-terrestrial secrets.
Theories suggest engineers examine crashed spacecrafts — and even hold meetings with aliens from across the galaxy.
The crash of a weather balloon at Roswell, New Mexico in 1947 sparked wild theories of an alien ship crash.
Some have suggested Area 51 is still storing parts of the crashed ship — or even its alien inhabitants.
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Dugway Proving Ground - Utah, USA
Dugway proving ground is the main biological and chemical weapons testing site for the US Army.
The top secret facility is sprawled across the Utah desert and develops new ways of working with deadly weapons.
Workers at the facility handle some of the most dangerous biological and chemical agents on the planet, including anthrax and other nerve agents.
In 1968, researchers working at the facility accidentally release the nerve gas VX into the air, killing thousands of sheep in Tooele County's Skull Valley.
Unsurprisingly, the base is kept tightly under wraps to preserve classified US military research.
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Unnamed base - Saudi Arabia
Another base unearthed by Google satellite snaps, this unnamed base in Saudi Arabia is yet to be officially recognised by the US government.
The remote airstrip deep in the Saudi desert is more than likely a secretive base for Predator and Reaper drones.
Its hangars bare resemblance to other US drone bases across the world.
Two former American intelligence officers told Danger Room that they thought the base was a drone centre.
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Area 25 – Nevada, USA
Area 25 was once used to test the rocket engines used by nuclear bombs during the 20th Century.
It's not far from Area's 51 and 6, and was strictly off-limits to civilians for several decades,
The site was so secretive that when a Mig-25 jet crashed nearby during a military test flight in 1984 journalists were quietly shepherded away.
Area 25 is now used for military exercises and training as well as tests on depleted uranium leftover from earlier projects.
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Area 51 "raid" organisers this week released a list of items alien "truthers" will need to storm military base.
A hidden military base from the 1860s was recently found buried beneath Alcatraz prison.
A skywatcher last week caught a rare glimpse of a secretive space plane owned by the US Air Force.
Which base do you think is creepiest? Let us know in the comments!
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