The AMES Type 80, sometimes known by its development rainbow code Green Garlic, was a powerful early warning (EW) and ground-controlled interception (GCI) radar developed by the Telecommunications Research Establishment (TRE) and built by Decca for the Royal Air Force (RAF). It could reliably detect a large fighter or small bomber at ranges over , and large, high-flying aircraft were seen out to the radar horizon. It was the primary military ground-based radar in the UK from the mid-1950s into the late 1960s, providing coverage over the entire British Isles.
In the late 1940s, the RAF developed the ROTOR plan to provide radar coverage over the UK in a phased rollout. As part of Stage 2, a new EW radar with long range would be deployed starting in 1957. A TRE research project, Green Garlic, appeared to be able to fill this role years earlier. The first examples of the Type 80 were being installed in 1953 and became operational in 1955. New sites received updated Mark III models and some formed the Master Radar Stations (MRS) that directly directed air defences, filling the GCI role as well. The original ROTOR plans for over 60 stations was reduced by half, retaining only a small number of older radars to fill gaps. Many of the ROTOR operations rooms, only recently completed, were sold off.
The system was developed during a period of rapid development in both radar technology and the nature of the strategic threat. The introduction of the hydrogen bomb led to serious questions about the nature of the defence, as a single bomber escaping interception was capable of causing catastrophic damage. Meanwhile, the introduction of the carcinotron radar jammer appeared to make such attacks much more likely to succeed. This led to plans to replace the Type 80s even before they were fully installed, relying on a much smaller network known as Linesman/Mediator with only three main sites. Two Type 80s were retained in this network for coverage over the North Sea, and several more were used for air traffic control.
Some of the Mark I models shut down as early as 1959 as the Mark III's increased range began filling gaps. Most of the UK fleet shut down in the late 1960s as Linesman's AMES Type 85s came online. The Type 80 also saw some overseas use by the RAF, with stations in Germany, Cyprus, Malta and Christmas Island. One was used by the Royal Canadian Air Force for operations around Metz. Four were used in Sweden. Potential sales for NADGE lost to a system from Thomson-CSF. The Swedish examples, Tom, Dick, Harry and Fred, were in use until 1978/79. The last Type 80, at RAF Buchan, shut down in 1993 after 37 years of operation. A total of about 35 Type 80s were built.
History Chain Home
By the middle of 1943, the UK's radar network was in a fairly complete form. It primarily used the Chain Home radars for early warning, supplanted by Chain Home Low and a handful of other special-purpose early warning designs. For fighter direction, or ground controlled interception (GCI) as it was known, the primary system was the somewhat more modern AMES Type 7, with smaller numbers of the advanced AMES Type 14 entering service late in the war. Starting in 1943, with the threat of German air attack waning, the Dowding system began to wind down operations. At the end of the war this process accelerated, as it was believed another war was at least a decade off.
To address the UK's needs during this expected interwar period, in 1945 Group Captain J. Cherry authored "A Memorandum on the Raid Reporting and Control Aspects of the United Kingdom Air Defense Organization", better known as the Cherry Report. It outlined a number of problems in the existing network and suggested a slow improvement to the equipment over the next decade. Much of the work detailed ways to improve the system by sending all of the radar data from the outlying stations to Master GCI stations, instead of having to hand data from station to station as aircraft moved about.
The Cherry Report was soon followed by a series of Defense White Papers covering all of the armed forces, calling for a rapid drawdown of military strength. In the area of air defence, they suggested moving the emphasis to research and development, as they expected there would be rapid technological improvement over the next few years and there was no point building existing designs that would soon be obsolete.
ROTOR
Events in the late 1940s led to a revaluation of this policy. These included the opening of the Korean War, the Berlin Airlift, and especially the test of the first Soviet atomic bomb in 1949. The Soviets were known to have built copies of the US Boeing B-29 as the Tupolev Tu-4, which could reach the UK while carrying one of these weapons. Several new reports on air defence were quickly produced. By 1950 these had resulted in two broad deployment plans, ROTOR and VAST, covering systems in the UK and overseas, respectively.
ROTOR was to be a two-phase program, initially providing coverage only in the "Core Defended Area" around London, and then gradually expanding to cover the entire British Isles over time. For Phase I, twenty eight of the wartime radar sites would be upgraded with new electronics, a further fourteen "Chain Early Warning" stations using the Type 14 and Type 13 would be added, along with eight new GCI stations with upgraded Type 7's. Many other wartime stations would be shut down. Control would be divided among six Sector Operations Centres, coordinating reports from the radars in their area. Phase I was to be completed by the end of 1952, or 1953 at the latest.
ROTOR Phase II would replace the early warning portions of the network with a dramatically more powerful Microwave Early Warning (MEW) radar, which would push the detection range out and give the operators more time to deal with aircraft that were now expected to be jet powered. It would also mean fewer stations would be needed to provide complete coverage, and the coverage would extend over the entire British Isles.
For both phases of ROTOR, shorter-range radars like the Type 7 and Type 14 would continue to fill the GCI role. It was understood that the GCI radars would have to be replaced at some point, and by 1950 there were several radar systems under consideration for this role. The two Phase II concepts were formalized under Operational Requirements OR2047 for the early warning system, and OR2046 for the GCI system.
It was also realized that passing the information from the early warning to the GCI radars would be problematic, so ROTOR also called for the construction of six Sector Operation Centers (SOCs) to coordinate the information being provided from the EW radars. Four of these were newly built underground bunkers, while two were rebuilt from WWII control centres. Plans began to develop a system to automatically forward information from the radars to the SOCs and combine it onto a single large display.
The cost of Phase I was enormous; £24 million for construction, £8.5 million for new electronics, and £19 million for telecommunications systems. In modern terms, this is £ million in . Despite this, the system was already seen to be almost useless against new jet powered aircraft. A report by the RAF Fighter Command's Air Officer Commander in Chief stated:
Green Garlic The ROTOR plans were taking place during a period of rapid technical development at the UK's radar research establishments — the RAF-oriented Telecommunications Research Establishment (TRE), the Army-oriented Radar Research and Development Establishment (RRDE), and the Navy's Admiralty Signal Establishment.
Among the important advances in the immediate post-war era were higher-power cavity magnetrons over 1 MW, and the introduction of new wide-bandwidth low-noise crystal detectors. In 1950, the TRE combined these crystal detectors with new electronics and produced a microwave-frequency receiver that added 10 dB of signal-to-noise ratio, slightly more than three times the sensitivity of previous designs. The radar equation is based on the 4th root of received energy, meaning that three times the energy results in about a 75% increase in effective range. Combining the new receiver with the more powerful magnetrons suggested a doubling of the effective range was possible.
To test these concepts, the TRE built a lash-up system using two antennas from the Type 14 radars, placing them side by side on a Type 7 turntable, and replacing the Type 14's 500 kW cavity magnetron with a new 1.5 MW model. The resulting system had an antenna that was effectively , with a beam-width of degree. The first example, known as Green Garlic, was operational on 18 February 1951, and a few days later it demonstrated its ability to detect de Havilland Mosquito and Gloster Meteor aircraft at ranges of , and track them continually at while flying at , a rather dramatic improvement over the roughly maximum range of the original Type 14. Against an English Electric Canberra at , the maximum range was increased to and tracking range to .
With relatively minor improvements, Green Garlic could fill most of the requirements of OR2047, yet do so years earlier than the MEW. This led to changes in the ROTOR plans so that these new radars, referred to within the plans as Stage IA, or Stage , would be deployed as part of ROTOR Phase II. Not only would the system be ready earlier than MEW, it would eliminate many of the existing WWII-era stations saving £1.6 million in installation costs, and another £1.5 million a year in continued operations. Almost all design effort within the TRE switched to the Stage IA, leaving little manpower available for the original MEW. MEW's development was spun off to Marconi Wireless Telephones.
Type 80 development Development of a production version of Green Garlic was mostly concerned with the design of an antenna that would provide more vertical coverage than the horizon-scanning pattern of the Type 14. A further increase in angular resolution was also desirable, and these two features led to a much larger antenna. This, in turn, led to the need for a more robust turntable than the Type 7. An added advantage of the larger antenna would be that the energy of the beam would be concentrated into a smaller angle, only of a degree. This allowed it to overpower jammers, a significant problem for the Type 7 where roughly 500 kW of power was spread over a 3 degree width.
An order for eight production units was delivered in July 1952, with Decca building the electronics, Currans the turntable assembly, and Starkie Gardiner the semi-parabolic reflector antenna. At this time the system was given the name AMES Type 80, separating them from wartime designs that were numbered in the teens. The first of the units would be purely experimental and would be installed at RAF Bard Hill, the following six units were expected to be installed through 1953 and be operational in mid-1954. This set of quickly installed systems was carried out under "Operation ROTOR 2".
The design's improved resolution allowed it to distinguish between closely spaced targets at , well over twice the range of the Type 7. That meant it could potentially fill the OR2046 GCI role as well. This would benefit from even higher angular resolution, but much more important was its ability to scan at higher altitudes so that the area above the station would be at least partially covered. Faster scanning rates would also be desirable. This could be accomplished through the design of a somewhat modified antenna, which became the AMES Type 81. However, as the Type 14 was seen as adequate in the short term, this project was given lower priority.