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The UK radar system was rapidly shut down at the end of the Second World War. At the time it was thought that it would be at least another decade ten years before another major conflict. The first Soviet nuclear test in 1949 and the outbreak of the Korean in 1950 quickly proved this to be wrong.

It quickly became clear that the major threat was the Soviet Union with the expectation being a major attack by Soviet Tu-4 bombers armed with 20 kT yield atomic bombs. With the delapidated state of the combined UK air defence it was unlikely that any attack would have effectively been detected or defended. The Cherry report of 1949 recommended an urgent overhaul and improvement of the UK's air defences, under the codename ROTOR. The report recommended that the network of 170 radar sites left over from the Second World War should be consolidated to 66 sites, and that the best existing radar be completely re-built to higher peacetime standards. The contract was awarded to the Marconi Wireless and Telegraph Company and was the largest government contract ever awarded to a UK firm.

At a time when rationing was still in place for some items the huge project consumed valuable resources in producing the re-manufactured radar equipment. It was felt the commitment was justified and the process resulted in massive improvements in reliability, performance and maintainability.

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. Whilst work continued on CEW 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.

Partly for economic reasons the ROTOR project was divided into two areas, east coast and west coast. 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 or semi-sunk bunkers. The distinctive feature of the east coast sites was the access/guardroom disguised as a bungalow which concealed an access corridor or shaft leading to a one, two or three level bunker. 

The ROTOR bunkers were known after the number of levels, R1 = single level, R2 = two level, R3 = three level and SOC = R4.

The bunkers were constructed by digging a massive hole, resolving issues such as water ingress, with the bunker then constructed in the hole then covered in 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.

At the top of the ROTOR hierarchy, four huge R4 SOCs were also built to provide command and control of the defences. Fighter Command split the UK into six sectors:

  • Scottish Sector: R4 SOC at Barnton Quarry
  • Northern Sector: R4 SOC at Shipton
  • Eastern Sector: R4 SOC at Bawburgh
  • Metropolitan Sector: R4 SOC at Kelvedon Hatch
  • Southern Sector: SOC at Box (WWII site re-used)
  • Western Sector: SOC at Langley Lane (WWII site re-used. Minor works were completed but the bunker was never equipped.)
In addition to this structure the AA guns of the Army got 28 protected Anti-Aircraft Operations Rooms (AAORs) in target areas. 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 issues experienced by any government led undertaking of this scale but two developments made the original ROTOR project redundant.

The development of the new Type 80 radar was completed in early 1953, this changed the whole concept of ROTOR. It was now possible to provide CEW and GCI functions at one installation. It was also found that on exercises, it was far easier to control the interceptors from the radar site itself, transferring data from the original ROTOR concept created too much of a delay.

In 1955 came the Soviet H-Bomb and the advent of supersonic high level bombers, it was now more important than ever that the UK's defence systems detected any inbound threat as early as possible. The original ROTOR concept was designed to combat 400mph piston engined war-era bombers, if could not cope with the new threat. It was at this time that the system of Master Radar Stations (MRS) was conceived.

The superior range of the new Type 80 radar meant that fewer sites were needed. Many ROTOR sites became Master Radar Stations but many more became redundant, this included the SOCs and the AAORs. The surplus sites, some less than two years old, were cleared and transferred to other government departments as war HQs.

Today many ROTOR sites remain, some having gone through several different owners and uses, and varying in states from intact to derelict to demolished.

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