Linesman/Mediator

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Linesman/Mediator was a dual-purpose civil and military radar network in the United Kingdom between the 1960s and 1984. The military side (Linesman) was replaced by the Improved United Kingdom Air Defence Ground Environment (IUKADGE), while the civilian side (Mediator) became the modern public-private National Air Traffic Services (NATS).

In the 1950s, the Royal Air Force was installing a radar network known as ROTOR using war-era radars like Chain Home along with new command centres. A new radar, the AMES Type 80, replaced all of the ROTOR radars and command centres with a series of nine Master Control Radars and a number of associated secondary radars. While these installations were in progress in the early 1950s, CSF introduced the carcinotron, which could output a radio signal at any desired frequency. This made it a very effective jamming system, and it appeared to render ground-based radars like Type 80 useless.

Considering several possible solutions, the RAF selected an experimental radar known as Blue Yeoman, but later known as the AMES Type 85. This radar changed its frequency with every pulse, making it impossible for carcinotron operators to know what frequency to jam. The RAF initially proposed an extensive network similar to the Type 80s, known as the "1958 Plan". This was abandoned in the aftermath of the 1957 Defence White Paper, which saw the threat to be moving from bombers to ballistic missiles, and argued the system should be cancelled. In late 1958, a much smaller system with only three main radars and a single control centre became "Plan Ahead", with its primary purpose being to provide air cover and anti-jamming support for a new anti-missile BMEWS radar.

During this same period, civilian air traffic was increasing dramatically and led to the 1962 formation of the National Air Traffic Control Services organization to handle national-scale air traffic control (ATC). Given enemy aircraft might hide among civilian ones, it was seen that combining data from Plan Ahead and the ATC system would have many advantages. Plan Ahead became Linesman and the ATC system Mediator. The centres would share locations in West Drayton, just north of Heathrow, Glasgow Prestwick Airport, and Mediator planned a third site in Preston, Lancashire. Ultimately all three Mediator sites were built, while only "L1" at West Drayton was ever completed as part of Linesman.

Whilst Mediator proceeded relatively smoothly, construction of Linesman was greatly delayed and it was not fully operational until March 1974. By that time the strategic threat had changed dramatically, and air strikes on the UK once again became a possibility. Linesman's single centralized L1 command centre was vulnerable, and the sea-side radars even more so. Money set aside to improve Linesman was instead directed to building its replacement, UKADGE. UKADGE was further expanded with Marconi Martello and the Type 85s stood down in the 1990s.