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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.

Work also began on a new microwave frequency radar to replace Chain Home c. 1957. The 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.

ROTOR called for the continual upgrading of the network over time, both the radars and the command and control systems. The introduction of the carcinotron radar jammer in the mid-1950s was a serious blow to these plans; 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 and ballistic missile greatly changed the nature of the strategic threat, and the idea of whole-country defence became untenable. 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.

A similar expedient system in the United States was the Lashup Radar Network.

As the threat of German air attack became ever more remote, UK radar operations were wound down late in the war, and by the time the war ended were already largely unused. When 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.^[1]

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.^[2] 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. Additionally, all of the sites would be upgraded with hardened bunkers to allow them to survive a near miss.^[3]

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.^[4] 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.^[5]

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, which was expected in the 1957 time-frame. Interception guidance would still be handled by existing systems in either case.^[2]

All of the radars were to be improved in terms of siting, with the addition of hardened control bunkers to protect the operators from a conventional attack. On the east coast, where a Soviet attack would be most likely, the bunkers were underground in the 'R' series (R1, R2, R3 and R4 etc.), while those on the western side of the UK were generally semi-sunken hardened structures ('R6') or above ground 'Secco' type huts (Hartland Point etc.). The R-series bunkers themselves were otherwise similar, featuring 10-foot-thick (3.0 m) concrete walls with all equipment, operations generators and air conditioning located inside.^[3]

Additionally, ROTOR re-arranged the existing RAF Fighter Command structure into six "Sector Operational Commands" (SOC) with their own command bunkers (three level 'R4' protected accommodation). Only four of these were built. Additional "Anti-Aircraft Operations Rooms" were built to coordinate the British Army's AA defences in the same overall system. The entire network of bunkers, radars, fighter control and command centres used up 350,000 tons of concrete, 20,000 tons of steel and thousands of miles of telephone and telex connections.

The work was mainly carried out by the Marconi Wireless and Telegraph Company in several phases, called ROTOR 1, ROTOR 2 and ROTOR 3.

As work on the Microwave Early Warning system began, researchers at the Royal Radar Establishment were experimenting with new cavity magnetrons and crystal detectors that, combined with a ad hoc antenna, increased the range of their existing microwave radars on the order of four times. While the resulting "Green Garlic" did not meet all of the requirements for the original MEW, it was close enough and would be available years earlier.

The decision was made to make the MEW a long-term development with additional features such as moving target indication while the Green Garlic would be mated to an enormous antenna that would give it range over 200 nautical miles (370 km; 230 mi). Installations, under the name AMES Type 80, began in 1954 with the first systems declared operational the next year. As installations continued, it was found that the accuracy was such that it could also be used to direct the interceptors, with no need to forward the information to the ROTOR control centres. By concentrating all of the plotting at a single site the total number of operators was greatly reduced.

As a result of the introduction of the Type 80, many of the existing ROTOR sites were rationalized into Master Radar Stations (MRS), while the rest were made redundant, some only two years after opening. During the same period, the introduction of the first surface-to-air missiles rendered the anti-aircraft guns obsolete, and the Army handed the air defence mission entirely to the RAF. All of the AAOR sites were closed.

A few of the ROTOR and AAOR stations were re-used for Regional Seats of Government or local authority wartime headquarters. Until the end of the Cold War, many of the sites were retained by the government. They were later sold to private buyers, converted into museums (for example Hack Green) or transferred to the National Air Traffic Control Centre.

RAF Aird Uig

Anstruther

Barnton Quarry

Bawburgh

RAF Beachy Head

RAF Bempton

RAF Boulmer

Box

Buchan

Calvo

RAF Charmy Down

Chenies

Cold Hesledon

Comberton

Crosslaw

Danby Beacon

Douglas Wood

Drone Hill

Drytree

Dunkirk

Fairlight

Faraid Head

Folly

Foreness

Gailes

RAF Goldsborough

Hack Green

Hartland Point

Hayscastle Cross

High Street

Hill Head

RAF Holmpton

Hope Cove

Hopton

Inverbervie

Kelvedon Hatch

Kilchiaran

Killard Point

Langtoft

Longley Lane

Murlough Bay

Neatishead

Netherbutton

Pevensey

Poling

Portland

Prestatyn

RAF Ringstead

Rye

Sandwich

RAF Saxa Vord

Scarinish

School Hill

Seaton Snook

Sennen

RAF Shipton

Snaefell

Sopley

St Annes

St Margarets

St Twynnells

Staxton
Wold

Stenigot

Stoke Holy Cross

Swingate

Trelanvean

Treleaver

Trerew

Trewan Sands

Trimingham

Truleigh Hill

Ventnor

RAF Wartling

West Beckham

West Myne

West Prawle

Wick

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Locations of former ROTOR sites in the United Kingdom

At the Radar Research Establishment in Malvern, Worcestershire a ROTOR bunker was constructed above ground to allow equipment to be tested in an operational environment. The building, locally designated as H Building, originally incorporated a replica of the sector operations centre at RAF Bawburgh. The building was demolished June 2020.^{[citation needed]}

RAF Staxton Wold is the only Chain Home site still used as a military radar site but with no remains of the CH station on site after being rebuilt for Linesman/Mediator in 1964. Today it is the former home of an RAF TPS 77 RRH (remote radar head).^[6]

RAF Boulmer is a working RAF building, which is housed in an ex-"ROTOR" R3 RAF Boulmer ('EZS') GCI R3 ROTOR Radar Station & Control and Reporting Centre in the UK Air Surveillance and Control System.

In terms of current condition, the ROTOR sites vary from demolished to intact.

For example, West Myne^[7] in Somerset was the last ROTOR 3 CHEL site. It was completed in 1957 after the introduction of the Type 80 radar and after many ROTOR stations had already closed. The site was within Exmoor National Park and its creation was strenuously opposed by the National Trust who lost no time in obliterating the site immediately after closure.

Many of the buildings have been re-purposed since being active as ROTOR sites. An example is the Bawburgh R4 SOC^[8] which was re-purposed as SRHQ4.1 and then RGHQ4.1 to suit the evolving needs of government. The building is intact, but it has been significantly reconfigured since its use as a ROTOR SOC, notably with the addition of an extra floor and the flooring-over of the original R4 operations well.

July 2019; Kent Underground Exploration are starting talks with TDC hoping to be given access to find and uncover the Foreness, Kent station which grid ref is TR 385710

• Gough, Jack (1993). Watching the Skies: The History of Ground Radar in the Air Defense of the United Kingdom. Her Majesty's Stationery Office. ISBN 9780117727236.
• Morris, Alec (1996). "UK Control & Reporting System from the End of WWII to ROTOR and Beyond". In Hunter, Sandy (ed.). Defending Northern Skies. Royal Air Force Historical Society.

• Cold War: Building for Nuclear Confrontation 1946-89, Cocroft, Thomas and Barnwell, English Heritage 2003, ISBN 1873592817

• The ROTOR radar system
• R3 Anstruther bunker, now a museum
• The Rotor Radar System, explanations & photographs
• Page about ROTOR at Subterranea Britannica
• Map of 'retained' CH sites and ROTOR sites