ROTOR was an elaborate air defence radar system built by the British Government in the early 1950s to counter possible attack by Soviet bombers. To get it operational as quickly as possible, it was initially made up primarily of WWII-era systems, notably the original Chain Home radars for the early warning role, and the AMES Type 7 for plotting and interception control. Data from these stations was sent to a network of control stations, mostly built underground, using an extensive telephone and telex network. A similar expedient system in the United States was the Lashup Radar Network.

ROTOR called for the continual upgrading of the network over time, both the radars and the command and control systems. Among these upgrades was a new microwave frequency radar to replace Chain Home c. 1957. An experimental system, Green Garlic, was so successful that it began replacing Chain Home starting in 1954. In service, these proved so accurate that they could replace the Type 7 radars as well, and their greatly improved range meant that fewer radars would be needed to provide coverage over the entire United Kingdom. This led to the Master Radar Stations that filled both early warning and ground controlled interception roles. The original ROTOR plans for 66 radars was repeatedly reduced, ultimately only requiring half that number of stations. Many of the operations rooms, recently completed, were sold, and the original concept of ROTOR with centralized command and control was abandoned.

The introduction of the carcinotron radar jammer in the mid-1950s was a serious blow to the system; a single aircraft carrying a carcinotron could jam the ROTOR radars so completely that they were rendered useless. At the same time, the introduction of the hydrogen bomb meant that aircraft could deliver a catastrophic blow. The idea of whole-country defence became untenable, there was simply no way to stop every aircraft, especially in the presence of jamming. The introduction of the ballistic missile resulted in further dramatic changes in the nature of the strategic threat. The only way to defend against missile attacks was deterrence, and if that failed, interceptor aircraft and missiles would have no measurable effect on the eventual outcome.

ROTOR was initially to be replaced by a new network dedicated largely to defending the V-bomber force, the "1958 Plan". This role was eventually abandoned, leaving only the task of locating aircraft carrying jammers to keep the BMEWS radars free from interference and prevent a successful sneak attack by missiles. Such a system did not require a large number of radars nor country-wide coverage. To reduce the cost of this much smaller network, studies on integrating the military radars with civilian air traffic control led to the Linesman/Mediator system of only five primary stations. The original ROTOR was replaced by Linesman in stages, starting in 1967.

As the threat of German air attack became ever more remote, UK radar operations were wound down late in the war, and by the end they were already largely unused. After the war ended, there was a general feeling that another war was at least ten years in the future. Given the rapid ongoing improvements in radar systems through this period, the Air Ministry felt there was no point introducing new radars that would likely become obsolete in a few years. They planned to allow radar to continue developing through this period and use the existing WWII-era systems in the meantime.

To consider the issue in more depth, the Cherry Report was commissioned in 1945. This report noted that the increasing speeds of new bombers, and especially future designs that were jet-powered, would travel across the plotting boards of the existing Dowding system so rapidly that they would fly off the maps before the interception could be arranged. The report suggested that a radar with 250 miles (400 km) range would be needed to replace the existing AMES Type 7/GCI systems, which were limited to about 90 miles (140 km) against bomber-sized targets. Estimating that such a radar would be available around 1957, the report suggested that existing GCI stations should receive upgraded antennas with more accuracy, new electronics for better performance, upgrades to their display systems, four Type 13's for height measuring, and two Type 14 units for anti-jamming use. Additionally, their information would be sent to six new command centres, who would produce much larger maps of the airspace, up to 1,000 miles (1,600 km) across. All of the sites would be upgraded with hardened bunkers to allow them to survive a near miss.

The Berlin Blockade of July 1948 led to concerns about the next war's estimated time-frame. A White Paper on the state of the network was completed in March 1949. This found that the stations were in a terrible state, with many of them suffering weather damage and a number of them having been broken into and vandalized. A complete defense would also require 1152 fighters and 265 AA regiments, of which only 352 fighters and 75 regiments were actually available. All of this was given extreme urgency with the 29 August 1949 test of the first Soviet atomic bomb. That month, a new directive stated RAF Fighter Command's mission was the defense of Great Britain.

It was known that the Soviets had made exact copies of the B-29 Superfortress as the Tupolev Tu-4, and these aircraft had the performance needed to reach the UK with a nuclear payload. These were fast, but not fast enough to escape the existing radars if they were upgraded as the Cherry Report suggested. Most of the new network would be made up of 28 rebuilt Chain Home systems, while the rest were taken from the existing selection of Chain Home Low, Chain Home Extra Low and the various Ground-controlled interception (GCI) radars. This was, in part, a stop-gap measure anticipating the availability of the dramatically improved radar, which was now known as the Microwave Early Warning (MEW), which was expected in the 1957 time-frame. Interception guidance would still be handled by existing systems in either case.