RAF Menwith Hill is a Royal Air Force station near Harrogate, North Yorkshire which provides communications and intelligence support services to the United Kingdom and the United States of America. The site contains an extensive satellite ground station and is a communications intercept and missile warning site and has been described as the largest electronic monitoring station in the world.

Menwith Hill Station was established in 1956 by the US Army Security Agency (ASA). Menwith Hill was operated by ASA from 1958 until its turnover to NSA in June 1966. The Army 713th MI Group remains the Executive Agent for the NSA Menwith Hill field site, which was awarded the NSA’s “Station of the Year” prize for 1991 after its role in the Gulf War. The Air Intelligence Agency 451st Intelligence Squadron (451 IS) as an integral part of Menwith Hill Station (MHS). Inside the closely-guarded 560 acre base are two large operations blocks and many satellite tracking dishes and domes. Initial operations focused on monitoring international cable and microwave communications passing through Britain. In the early 1960s Menwith Hill was one of the first sites in the world to receive sophisticated early IBM computers, with which NSA automated the labor-intensive watch-list scrutiny of intercepted but unenciphered telex messages. Since then, Menwith Hill has sifted the international messages, telegrams, and telephone calls of citizens, corporations or governments to select information of political, military or economic value.