Royal Air Force Menwith Hill is a Royal Air Force station near Harrogate, North Yorkshire, England, which provides communications and intelligence support services to the United Kingdom and the United States. The site contains an extensive satellite ground station and is a communications intercept and missile warning site. It has been described as the largest electronic monitoring station in the world.
RAF Menwith Hill is owned by the Ministry of Defence (MoD), but made available to the US Department of Defense (DoD) under the NATO Status of Forces Agreement 1951 and other, undisclosed agreements between the US and British governments. Her Majesty's Government (HMG) is entitled to possession of the site and retains control over its use and its facilities, though the administration of the base is the responsibility of the US authorities, with support provided by around 400 staff from Government Communications Headquarters (GCHQ), in addition to United States Air Force (USAF) and US National Security Agency (NSA) personnel. In 2014, the number of American personnel was reduced as part of a streamlining of operations due to improvements in technology.
The site acts as a ground station for a number of satellites operated by the US National Reconnaissance Office, on behalf of the NSA, with antennae contained in numerous distinctive white radomes, locally referred to as "the golf balls", and is alleged to be an element of the ECHELON system.