The UK radar system was rapidly run down after the end of the Second World War. It was then envisaged that it would be at least another ten years before another conflict in the European / Atlantic theatre, but the first Soviet nuclear test in 1949, and cold war changed this view irreparably. 

The perceived threat was the Soviet Tu-4 long-range four engine bombers armed with 20 Kt yield atomic bombs. It was doubtful that the run down state of the UK's air defences that they could have been detected and intercepted. In 1949 the Cherry report recommended an urgent overhaul and improvement of the UK's air defences, under the codename Rotor. It was recommended that a network of some 170 radar sites left over from the last war be rationalised and consolidated to 66 sites, and that the best existing radar be completely re-built to higher peacetime standards. The essential elements of the wartime Control and Reporting structure was to be retained: - a hierarchical command and control system, separate sectors etc. The contract was given to the Marconi Wireless and Telegraph Company and was the largest government contract awarded to a UK firm.

 The re-manufactured radar equipment consumed valuable manpower and resources, at a time when the country was under dire economic circumstances, with rationing still in place for many items. But this effort resulted in massive improvement in reliability and maintainability, as well as performance: some equipment had its range more than doubled. All achieved in complete secrecy. 

 Research commenced on a new Centimetric Early Warning (CEW) radar, code named Green Garlic, later known as Type 80, as a replacement for the Chain Home / Ground Controlled Intercept radars. But for the meantime the primary long-range warning came from 28 selected rebuilt coastal Chain Home sites. 38 other sites were chosen for a variety of roles: Chain Home Extra Low (CHEL), CEW and GCI, using standardised sets of equipment: either the Type 7 or 11 GCI sets or the Type 13 and 14 centimetric sets.

 The Rotor project was divided into two areas, east coast and west coast, partly as an economy measure. The threat was seen as higher on the east coast, so the majority of the sites had underground-protected operations rooms. The west coast had mainly surface bunkers or semi-sunk ones. The distinctive feature of the east coast sites was the bungalow, which served as access/guardroom to the bunkers. The bungalow concealed an access corridor, which led to a one-, two- or three-level bunker.

 These bunkers were known as R1 for single level bunkers, R2, R3 and the SOC - R4. In construction, a massive hole was first dug and usually extensive de-watering had to take place. The bunker was then constructed and buried under earth. The bunker had 10-foot thick ferro-concrete walls, complete with its own borehole, generators and filtered air conditioning. They were supposed to give protection against a near miss by a 20 kT nuclear weapon. The west coast sites had similarly massive bunkers, but built on the surface.

 The whole Rotor programme consumed 350,000 tons of concrete, 20,000 tons of steel and thousands of miles of telephone and telex connections. The project progressed with the usual delays. But two developments came like a bombshell.