Menwith Hill Station was established in 1956 by the US Army Security Agency (ASA) and is a Crown freehold site belonging to the Ministry of Defence. It was known as the 13th US Army Security Agency Field Station. It was operated by the ASA from 1958 until its turnover to the NSA in June 1966. It was given the designation RAF Menwith Hill on 19 February 1996 (and became its Field Station F83), a simple administrative change to bring the station into line with other RAF sites made available by the Ministry of Defence to the US Government.
There is no security of tenure agreement in place at RAF Menwith Hill - assurances were given to the US authorities in 1955 and again in 1976 that the site would be made available to the US Forces by Her Majesty's Government for a period of 21 years (known as the security of tenure agreements) and were given to facilitate the commitment of US funding to the station.
In the early 1960s the station was one of the first sites in the world to receive sophisticated early IBM computers. These were used by the NSA to automate the labor-intensive tasks of scrutinising all those intercepted telex messages.
Until 1974 the station's speciality was the interception of International Leased Carrier (ILC) signals - the communications links run by civil agencies - the Post, Telegraph and Telephone ministries of eastern and western European countries. The station worked very closely with the British Post Office with a scheme to build a chain of microwave radio towers. This system was named 'Backbone' and was supposed to provide emergency links if Britain was attacked but when it was completed it turned out to be feeding signals directly into the intelligence base at Menwith Hill instead.
In the 1980s it developed a new operations block codenamed Steeplebush to expand its programme of satellite surveillance. A second phase, Steeplebush II, was developed in the early 1990s. A third is believed to be in preparation.