existing radars were also planned. The existing Type 80 radars used in the MRS network were powerful but relatively easy to jam. Upgrades were aimed primarily at offering improved jamming resistance in the event of a noisy ECM environment. To augment the existing Type 80 a new Type 84 radar had already been proposed. Linesman proposed that three new radars were developed, two primary long-range search radars; Marconi's Type 84 and the AEI Type 85 "Blue Yeoman", with additional height finding capability being provided by the Decca HF 200 height-finder. To improve system resilience to jamming the two primary radars operated on different frequency bands, the Type 84 in "L" band, the Type 85 in "S" band. As the system developed more systems were added to improve the ECM capability of the system. During various reviews of Linesman and the "Ahead" plan it was decided to incorporate civilian air traffic control, the "Mediator" portion of the plan. Linesman and Mediator were now considered jointly, although this led to escalating costs and the subsequent need to scale down the original plan. Whilst the L1 was originally intended to be underground at Bawburgh, Norfolk, cost cutting between 1960 and 1962 led to a prototype of the L1 system being set up above-ground in Building 123 at West Drayton in 1963. The Mediator element set up LATCC (London Air Traffic Control Centre) in a building nearby. LATCC used the Linesman data in their Marconi Myriad computers to handle all air traffic control in the London area. Here the main manufacturers (Plessey – data processing, and Marconi – displays) carried out enhanced development. Each of the Linesman sites was able to operate on its own, but the network was intended to be controlled from the centralized "L1" site (now at West Drayton). Each of the field stations sent data to L1 over microwave links, eventually phone lines, where it was recombined to form a country-wide view of the airspace; a Recognized Air Picture (RAP). The original central computer system for Linesman consisted of 21 Plessey XL4 and XL6 germanium computers, integrated as the Radar Data Processing System (RDPS). These computers worked together using random highways that were a very early version of a Local Area Network. The 21 RDPS computers then worked to assemble the Recognised Air Picture (RAP) which covered an area 1024 by 1024 nautical miles over the British Isles. Three more