A surveillance station in Yorkshire was used to intercept satellite communications across the world, and shared this data with US spy satellites, according to the latest documents to be published from the stash leaked by US National Security Agency (NSA) whistleblower Edward Snowden in 2013.
The aim, at the time, was to target internet cafés and other sources of communications in the Middle East.
The documents show that Menwith Hill ran a programme to collect as much data as possible. GCHQ and the NSA had tools to collect (Asphalt), survey (Blacktop), process (Tarmac) and exploit (GTE/Index) the information.
The programme arose following an instruction from lieutenant general Keith Alexander in June 2008, then director of the NSA. "Why can't we collect all of the signals, all the time? Sounds like a good summer homework project for Menwith," he was reported as saying.
GCHQ responded by investing more than £30m on a new operations building at Menwith Hill with the ability to store and analyse a vast amount of intercepted communications.
The investment included a 200-seat auditorium to host classified operations meetings and other events, according to documents recently released by The Intercept, one of the outlets acting as custodian for the millions of documents leaked by Snowden.
The documents indicate that the investment between 2009 and 2011 allowed Menwith Hill to increase the level of signals processed from 140 out of 9,000 to almost all of the satellite signals that it targeted.
Menwith Hill exists officially to provide "rapid radio relay and conduct communications research", but in reality its activities have increasingly focused on eavesdropping, particularly on satellite communications.
The facility also takes data feeds from US spy satellites in orbit above countries of interest, which can capture signals from mobile phones and wireless networks.
The intelligence is fed into a programme called Ghosthunter, which focuses on targets in the Middle East "to learn and establish pattern of life for known terrorists who use internet cafés to communicate".
Relatively poor connectivity means that internet cafés in places like Yemen and Afghanistan tend to route communications via poorly secured VSAT systems that relay traffic at up to 16Mbps via commercial satellites in geosynchronous orbit.
However, while the latest documents provide new information about the activities conducted in places like Menwith Hill, and how the information has been used, the extent of Alexander's injunction to "collect all of the signals" remains unclear.
It is also not known whether such information gathering techniques are aimed at the UK, Europe and even the US.
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