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The Improved United Kingdom Air Defence Ground Environment, normally shortened to either UKADGE or IUKADGE, was the
Royal Air Force The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
's (RAF)
ground-controlled interception Ground-controlled interception (GCI) is an air defence tactic whereby one or more radar stations or other observational stations are linked to a command communications centre which guides interceptor aircraft to an airborne target. This tactic wa ...
system covering the
British Isles The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...
during the 1990s. It consisted of a number of ground-based radar sites, links to
airborne early warning An airborne early warning and control (AEW&C) system is an airborne radar early warning system designed to detect aircraft, ships, vehicles, missiles and other incoming projectiles at long ranges, as well as performing command and control of t ...
aircraft and
Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
ships, a telecommunications system to send digital data and voice communications on a protected network, and processing systems based on
VAX-11/780 The VAX-11 is a discontinued family of 32-bit superminicomputers, running the Virtual Address eXtension (VAX) instruction set architecture (ISA), developed and manufactured by Digital Equipment Corporation (DEC). Development began in 1976. In ad ...
computers. The network ultimately contained a dozen long-range radars including four
Marconi Martello Martello is a family of phased array radar systems developed by Marconi Electronic Systems in the 1970s and introduced operationally in the early 1980s. They provided long-range early warning radar, early warning capabilities but also had the accu ...
, two General Electric TPS-592, and six
Plessey AR-320 The AR-320 is a 3D early warning radar developed by the UK's Plessey in partnership with US-based ITT-Gilfillan. The system combined the receiver electronics, computer systems and displays of the earlier Plessey AR-3D with a Gilfillan-developed ...
. UKADGE was developed in response to concerns about its predecessor,
Linesman/Mediator Linesman/Mediator was a dual-purpose civil and military radar network in the United Kingdom between the 1960s and 1984. The military side (Linesman) was replaced by the Improved United Kingdom Air Defence Ground Environment (IUKADGE), while the ...
. Linesman started in the 1950s, when it was assumed that any air attack on the UK would be by
hydrogen bomb A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lo ...
so no effort was made to "harden" the radars or its main control centre as such effort would be futile. By the mid-1960s, with the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
reaching strategic parity with
NATO The North Atlantic Treaty Organization (NATO ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...
, such an attack no longer seemed likely; it was assumed a war would have a protracted conventional stage, perhaps never going nuclear. In this environment, the highly exposed Linesman system was a target for attack by conventional weapons. UKADGE was intended to be highly survivable in this sort of war. It replaced Linesman's fixed communication links with a
packet switching In telecommunications, packet switching is a method of grouping Data (computing), data into short messages in fixed format, i.e. ''network packet, packets,'' that are transmitted over a digital Telecommunications network, network. Packets consi ...
network sending data to multiple command centres around the country. Radar sites had the ability to control interceptions by themselves, while the overall recognised air picture was compiled and directed at Strike Command headquarters. To complicate the use of
radar jammer Radar jamming and deception is a form of electronic countermeasures (ECMs) that intentionally sends out radio frequency signals to interfere with the operation of radar by saturating its receiver with noise or false information. Concepts that blan ...
s, several new radars were introduced that operated across a wide band of frequencies from L to S (C to F in
NATO The North Atlantic Treaty Organization (NATO ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...
terms). Peacetime radars were located at existing radar sites re-used from Linesman, while additional radars were ready to be set up at pre-surveyed locations. Like Linesman before it, UKADGE soon ran into major delays. It was not declared operational until 1 June 1993, six years late, by which time the ending of the
Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...
had led to a loss in interest in the programme. Even at that date, the system was missing a number of components and required considerable remedial work. By the 2000s, the system was increasingly difficult to maintain as many of the equipment vendors had since gone out of business or abandoned their product lines. In 2001,
IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...
won a contract to rebuild the command and communications portions of the system, which emerged as the current
Air Surveillance and Control System An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...
(ASACS), which is in the process of being replaced by the new Project Guardian.


History


Defence in the nuclear era

In 1957,
Duncan Sandys Duncan Edwin Duncan-Sandys, Baron Duncan-Sandys (; 24 January 1908 – 26 November 1987), was a British politician and minister in successive Conservative governments in the 1950s and 1960s. He was a son-in-law of Winston Churchill and played a ...
introduced his Defence White Paper which, among other topics, considered the effect of the introduction of
ballistic missile A ballistic missile is a type of missile that uses projectile motion to deliver warheads on a target. These weapons are powered only during relatively brief periods—most of the flight is unpowered. Short-range ballistic missiles (SRBM) typic ...
s on the UK's defensive posture. Continuing the prevailing notion that any attack on the UK would be nuclear, the paper suggested that future attacks would likely be made by ballistic missiles. As there was no defence against these weapons, the only possible way to stop them would be to deter them. This meant the
V bomber The "V bombers" were the Royal Air Force (RAF) aircraft during the 1950s and 1960s that comprised the Nuclear weapons and the United Kingdom, United Kingdom's strategic nuclear strike force known officially as the V force or Bomber Command Mai ...
force had to be able to launch with extreme rapidity. At the time, the
Royal Air Force The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
(RAF) had been planning a new nationwide anti-bomber radar network known as Plan Ahead. This was, conceptually, a replacement for the earlier network of
AMES Type 80 The Air Ministry Experimental Station, AMES Type 80, sometimes known by its development rainbow code Green Garlic, was a powerful early-warning radar, early warning (EW) and ground-controlled interception (GCI) radar developed by the Telecommuni ...
radars, using fewer but longer-ranged radars. The main goal was to counter the
carcinotron A backward wave oscillator (BWO), also called carcinotron or backward wave tube, is a vacuum tube that is used to generate microwaves up to the Terahertz radiation, terahertz range. Belonging to the traveling-wave tube family, it is an electroni ...
jammer, which rendered the Type 80 almost useless. Another problem was the ever-increasing civilian air traffic, which confused the picture seen by the Type 80 operators. Plan Ahead would send all of its information to two underground locations where the radar data would be compared to known civilian
flight plan Flight plans are documents filed by a aviator, pilot or flight dispatcher with the local Air Navigation Service Provider (e.g., the Federal Aviation Administration, FAA in the United States) prior to departure which indicate the plane's planned ...
s, targets separated out, and directions sent to the
interceptor aircraft An interceptor aircraft, or simply interceptor, is a type of fighter aircraft designed specifically for the defensive interception role against an attacking enemy aircraft, particularly bombers and reconnaissance aircraft. Aircraft that are c ...
. It was felt this could only be accomplished at centralised stations that had all of the data on both military and civilian aircraft. As part of ongoing discussions, brought to a head with the release of the White Paper, Plan Ahead was put in doubt. There was no purpose in defending against bombers if the attack came by missiles, and it seemed unlikely the detection of a bomber attack would not also indicate missiles were on the way. The V bombers would have to launch on any credible sign of an attack in either case. The only clear role for the radars appeared to be to indicate an attack was coming and give time for the V force to launch; actually plotting a response seemed superfluous as the V force would (hopefully) be gone by the time the attack landed. What was really needed was a new radar dedicated to detecting a missile launch. After rapidly completed negotiations, the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
agreed to move one of their new
BMEWS The RCA 474L Ballistic Missile Early Warning System (BMEWS, 474L System, Project 474L) was a United States Air Force Cold War early warning radar, computer, and communications system, for ballistic missile detection. The network of twelve radar ...
radars to the UK, initially to Scotland, but later to Yorkshire at
RAF Fylingdales Royal Air Force Fylingdales (RAF Fylingdales) is a Royal Air Force List of Royal Air Force stations, station on Snod Hill in the North York Moors, England. Its motto is ''Vigilamus'' ("We are watching"). It is a radar Military base, base and i ...
where it could be better protected. This led to a new concept for Plan Ahead that removed most air defences, and shrunk the area covered by radar to that around the air and missiles bases in the Midlands.


Linesman

Meanwhile, the level of civilian air traffic was growing rapidly and badly needed new radars and automation. Studies began to see if Plan Ahead could be combined with the
air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled air ...
(ATC) network, allowing both users to share their radar coverage. This concept was accepted, and on 22 February 1961, Plan Ahead became the Linesman half of the
Linesman/Mediator Linesman/Mediator was a dual-purpose civil and military radar network in the United Kingdom between the 1960s and 1984. The military side (Linesman) was replaced by the Improved United Kingdom Air Defence Ground Environment (IUKADGE), while the ...
system. As part of this change, the civilian and military sides would have the share data, which resulted in the military centre being moved to London so it could be as close as possible to its civilian counterpart. In the era of a three-day war and attacks by
hydrogen bomb A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lo ...
s, any attempt to harden the centre seemed futile, so the building was located aboveground. The RAF was adamantly opposed to this change, stating that control over the interceptor force should take place at the radar stations so the failure of the centralized centre would not render the system useless at a stroke. The Treasury was unwilling to release any funds for the equipment needed to plot at the radars. Linesman quickly ran into problems and it was clear by 1964 that it would not be completed on time. Whilst the radar systems were complete by 1968, the computerized systems used to collate the information from them was repeatedly delayed. Much of the blame was laid on
Plessey The Plessey Company plc was a British electronics, defence and telecommunications company. It originated in 1917, growing and diversifying into electronics. It expanded after World War II by acquisition of companies and formed overseas compani ...
, whose previous experience in telephone switching left them unprepared for the level of programming support needed. Eventually, programmers from the
Atomic Weapons Research Establishment } The Atomic Weapons Establishment (AWE) is a United Kingdom Ministry of Defence research facility responsible for the design, manufacture and support of warheads for the UK's nuclear weapons. It is the successor to the Atomic Weapons Researc ...
had to be sent to help. Meanwhile, because all of the interception task was now moved to a single building, it had to grow much larger. Eventually nine major contractors were working on the system, adding coordination problems.


Conventional war

While the Linesman installation dragged on, the strategic situation was once again changing. Previously,
NATO The North Atlantic Treaty Organization (NATO ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...
assumed a tripwire force concept where conventional forces were not expected to actually stop
Warsaw Pact The Warsaw Pact (WP), formally the Treaty of Friendship, Co-operation and Mutual Assistance (TFCMA), was a Collective security#Collective defense, collective defense treaty signed in Warsaw, Polish People's Republic, Poland, between the Sovi ...
forces. Instead, any attack on these forces would be responded to with
tactical nuclear weapon A tactical nuclear weapon (TNW) or non-strategic nuclear weapon (NSNW) is a nuclear weapon that is designed to be used on a battlefield in military situations, mostly with friendly forces in proximity and perhaps even on contested friendly territ ...
s against the Pact forces and high-value targets. If this failed to stop the war, a "
massive retaliation Massive retaliation, also known as a massive response or massive deterrence, is a military doctrine and nuclear strategy in which a state commits itself to retaliate in much greater force in the event of an attack. It is associated with the U. ...
" using strategic weapons would be launched against the USSR. NATO's massive
air superiority An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmospher ...
ensured the attack would succeed. In July 1964, the US
Joint Chiefs of Staff The Joint Chiefs of Staff (JCS) is the body of the most senior uniformed leaders within the United States Department of Defense, which advises the president of the United States, the secretary of defense, the Homeland Security Council and ...
admitted that the Soviet nuclear forces would survive in enough number to guarantee their own massive retaliation. The US could no longer risk the Soviets using their strategic force and began emphasising their conventional weapons. The UK's own
Exercise Hell Tank Exercise Hell Tank (sometimes Helltank) was a series of military exercises carried out by the British Army of the Rhine (BAOR) in 1966 and 1967 to study the use of the helicopter in the anti-tank role. A follow-up test in 1969, Exercise Sparrow Ha ...
suggested a 45-to-1 kill ratio for helicopters over tanks, upsetting the entire concept of how to stop a Warsaw Pact invasion. Now it was believed the war would remain conventional for some time, or its entirety. In this scenario, an air attack on the UK could no longer be assumed to be nuclear and would no longer be deterred by the V bombers. There was nothing to stop the Soviets from attacking the Linesman sites and leaving the UK airspace entirely unprotected. Moreover, new Soviet aircraft with longer range allowed the UK to be approached from across the North Atlantic, where radars had been run down in keeping with Linesman's tripwire concept. This "back door" would allow the west coast to be attacked without any recourse. Other aircraft had the range to operate from Europe and approach the UK at low altitude, where they could not be seen by the Linesman radars, allowing them to be easily attacked. By 1971 the Linesman software was still nowhere near completion and there were murmurs that the project might be cancelled outright. In 1972, Labour MP Leslie Huckfield described the system as "one of the biggest confidence tricks ever perpetrated in Britain". Further, the systems had been designed for the civilian traffic levels of the 1950s and was now "less than half" what was required, leaving them overwhelmed. One programmer suggested that the system might work properly for about 10 minutes a week.


Calls for a new system

Starting in 1969, as the full scope of the Linesman disaster became clear, various groups in the RAF called for a major reorganization of the system. The Moulton Report of December 1969 stated that the system would never work as the computers were too overloaded and that the interception task should be moved to the radar sites. Non-essential systems, like digital communications with the fighters, should be abandoned. In September 1971, Air Commander John Nicholls published a report on Linesman outlining its many problems, notably the lack of coverage in the north and south, and its inability to deal with low-flying targets. The same month,
Air commodore Air commodore (Air Cdre or Air Cmde) is an air officer rank used by some air forces, with origins from the Royal Air Force. The rank is also used by the air forces of many countries which have historical British influence and it is sometimes ...
John Ellacombe published a similar report that suggested L1 be used for nothing more than the compilation of the recognized air picture and that several new radar stations be added. In November,
RAF Strike Command The Royal Air Force's Strike Command was the military formation which controlled the majority of the United Kingdom's bomber and fighter aircraft from 1968 until 2007 when it merged with Personnel and Training Command to form the single Air ...
called for the complete reformation of the entire network. Their plan devolved track assembly to a series of control centres which would forward that data to the Air Defence Centre where the recognized air picture would be assembled, along with the status of the various defensive systems. The Air Defence Commander would then send commands back to the control centres, who would carry out the interceptions. They also suggested abandoning the complex transmission system built for Linesman. This worked by capturing the entire "video" signal being sent to a
cathode ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms on an oscilloscope, a ...
display, using it to frequency modulate a
microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
signal, and then sending the resulting signal to L1 using wideband
microwave relay Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz (1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signal ...
s. Operators at L1 would then see the radar signals as they were at the stations, and use them to extract "tracks" of interest. However, this was forwarded to L1 using the
BT Tower The BT Communications Tower, also known simply as the BT Tower, is a Listed building, grade II listed Radio masts and towers, communications tower in Fitzrovia, London, England, owned by BT Group. It has also been known as the GPO Tower, the P ...
, which could be easily jammed by aiming a transmitter at it, as well as costing a lot of money to maintain. Strike Command noted that if the track extraction was being carried out at the radar stations, the resulting information, essentially an ID number, location and direction, could easily be sent in digital format over conventional telephone lines or narrow-band microwave links, as was being done in NADGE. Finally, they called for the replacement of the huge and costly radars like the
AMES Type 85 The AMES Type 85, also known by its rainbow code Blue Yeoman, was an extremely powerful early warning (EW) and fighter direction (GCI) radar used by the Royal Air Force (RAF) as part of the Linesman/Mediator radar network. First proposed in ea ...
with a greater number of simpler and cheaper systems.


IUKADGE takes shape

In January 1972, before Linesman was even operational, the ADGE System Study Group was organized to replace it. Their first report was delivered on 1 May 1972, and was largely a list of the problems in Linesman; low-level coverage was largely nonexistent, high-level coverage was limited in the north and south, L1 was highly vulnerable, and the data L1 collected was not available at Air Defence headquarters at
RAF High Wycombe Royal Air Force High Wycombe or more simply RAF High Wycombe is a Royal Air Force station, situated in the village of Walters Ash, near High Wycombe in Buckinghamshire, England. It houses Headquarters Air Command, and was originally designed ...
, only at L1 itself. The report also contained a longer consideration of the methods of sending track data around the system. They felt that advances in technology were making automatic track extraction possible and would significantly reduce total manpower. They also considered the low-level problem, examining solutions in the form of
over-the-horizon radar Over-the-horizon radar (OTH), sometimes called beyond the horizon radar (BTH), is a type of radar system with the ability to detect targets at very long ranges, typically hundreds to thousands of kilometres, beyond the radar horizon, which is t ...
s, radars on
oil platform An oil platform (also called an oil rig, offshore platform, oil production platform, etc.) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platforms w ...
s, and distributed systems run by the
Royal Observer Corps The Royal Observer Corps (ROC) was a civil defence organisation intended for the visual detection, identification, tracking and reporting of aircraft over Great Britain. It operated in the United Kingdom between 29 October 1925 and 31 Decembe ...
. They ultimately concluded that the only practical solution was
airborne early warning An airborne early warning and control (AEW&C) system is an airborne radar early warning system designed to detect aircraft, ships, vehicles, missiles and other incoming projectiles at long ranges, as well as performing command and control of t ...
. The final report, referring to the existing system as UKADGE, was published in August 1972. This suggested that there should be no changes to the existing radar sites other than the replacement of outdated systems like the AMES Type 13 with their modern replacements like the
Decca HF200 The HF200 is a height finder radar designed and first built by Decca Radar in 1957, and continuing sales into the 1970s after the division was purchased by Plessey in 1965. It was one of the company's successful heavy radar projects, winning the ...
. The "back door" approach over the
North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...
and Norwegian coast would be closed with radars at Buchan and in the Hebrides, and the southern area at Burrington, while another new radar would replace the Type 80 at Saxa Vord but officially be part of NADGE and paid for by NATO funds. Data from NADGE,
Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
ships and newly purchased airborne radar aircraft would also be injected into the network by radio links, and distributed over various telecommunications systems. On 18 December 1972, the Air Force Board accepted the reports and decided "that Phase 1 of the LINESMAN project should be completed but that, after commissioning, the L1 building should be operated and manned on only a limited basis ... Emphasis was to be placed on keeping expenditure to a minimum and high priority was to be given to the development of an alternative - less vulnerable - air defence system." Linesman was effectively being killed off. Several more commissioning dates came and went, until it was finally declared operational, in a limited form, on 21 March 1974. With the acceptance of the need for a new system, in 1972 Strike Command formed the Air Defence Environment Team, or ADET, to define a formal proposal and liaise with industry during construction. In the mid-1970s, Plessey won a contract to consider new layouts for the network. Their reports suggested that advances in computers and communications made a flexible system possible. After five years, ADET received Air Force Board approval and the organization moved to the
Ministry of Defence A ministry of defence or defense (see American and British English spelling differences#-ce.2C -se, spelling differences), also known as a department of defence or defense, is the part of a government responsible for matters of defence and Mi ...
(MoD) in 1977.


Formal definition

In 1979, a formal Air Staff Requirement 888 was issued for bids. ASR.888 defined the Improved Command and Control System, or ICCS, the network and computer systems that would connect together the various radar sites and control centres. It also defined the consoles that would be used to display that data. Two major bids were received, and in September 1980 the contract was won by the newly formed UKADGE Systems Limited, a consortium of
Hughes Aircraft The Hughes Aircraft Company was a major American aerospace company, aerospace and defense contractor founded on February 14, 1934 by Howard Hughes in Glendale, California, as a division of the Hughes Tool Company. The company produced the Hughes ...
,
Marconi Guglielmo Giovanni Maria Marconi, 1st Marquess of Marconi ( ; ; 25 April 1874 – 20 July 1937) was an Italian electrical engineer, inventor, and politician known for his creation of a practical radio wave-based wireless telegraph system. This ...
and Plessey. The only significant competition was a similar bid led by
Thomson-CSF Thomson-CSF was a French company that specialized in the development and manufacture of electronics with a heavy focus upon the aerospace and defence sectors of the market. Thomson-CSF was formed in 1968 following the merger of Thomson-Hous ...
which included
International Computers Limited International Computers Limited (ICL) was a British computer hardware, computer software and computer services company that operated from 1968 until 2002. It was formed through a merger of International Computers and Tabulators (ICT), English Ele ...
. The formal signing took place in 1981. Development overall was directed by Hughes, who selected the recently introduced
VAX-11/780 The VAX-11 is a discontinued family of 32-bit superminicomputers, running the Virtual Address eXtension (VAX) instruction set architecture (ISA), developed and manufactured by Digital Equipment Corporation (DEC). Development began in 1976. In ad ...
minicomputer A minicomputer, or colloquially mini, is a type of general-purpose computer mostly developed from the mid-1960s, built significantly smaller and sold at a much lower price than mainframe computers . By 21st century-standards however, a mini is ...
as the basis of the system. Marconi was to supply the display consoles and the voice communications systems. Plessey was to deliver a processor for the consoles which would handle the graphics display, and the digital communications switching systems. ASR.888 described a system with twelve main locations. Strike Command headquarters would host the Air Defence Operations Centre (ADOC), while ROC headquarters at
RAF Bentley Priory RAF Bentley Priory was a non-flying Royal Air Force station near Stanmore in the London Borough of Harrow. It was the headquarters of Fighter Command in the Battle of Britain and throughout the Second World War. The Royal Air Force station c ...
would host the backup Standby ADOC. The ADOCs were in charge of the overall command of the defence response and the maintenance of the recognized air picture, which would be fed data on civilian flights and jammer activity from the existing L1 site. The direct control of the aircraft and missiles would be handled at two Sector Operations Centres (SOCs) and their two backup Control and Reporting Centres (CRCs). Additional control consoles would be placed at four of the radar stations to form the Control and Reporting Posts (CRPs) while a further two radar sites lacking control posts would be known as Reporting Posts (RPs). The SOCs and CRCs would each have five VAX computers, two for processing the input/output from the network, one for processing radar data into tracks, one for processing jammer tracking, and the last for "general housekeeping" and as a warm-failover if any of the others failed. Data from the systems was sent to the Marconi consoles, which were based around a round four-colour display with two smaller monochrome text displays, "totes", one on either side. Each station also had four wall-sized four-colour displays, used primarily for presenting the recognized air picture and the status of available defences. After some time, the data and voice system was spun off to its own project, Uniter, which moved to GEC. Uniter was an early implementation of a nationwide
packet switching In telecommunications, packet switching is a method of grouping Data (computing), data into short messages in fixed format, i.e. ''network packet, packets,'' that are transmitted over a digital Telecommunications network, network. Packets consi ...
system based on the concepts recently introduced by the
NPL network The NPL network, or NPL Data Communications Network, was a local area computer network operated by the National Physical Laboratory (United Kingdom), National Physical Laboratory (NPL) in London that pioneered the concept of packet switching. ...
in the early 1970s. GEC had produced a commercial implementation for
British Telecom BT Group plc (formerly British Telecom) is a British Multinational corporation, multinational telecommunications holding company headquartered in London, England. It has operations in around 180 countries and is the largest provider of fixed-li ...
known as "System X" and proposed the same basic concept for Uniter. In addition to the land links, the SOCs and CRCs also had microwave links into the
British Army The British Army is the principal Army, land warfare force of the United Kingdom. the British Army comprises 73,847 regular full-time personnel, 4,127 Brigade of Gurkhas, Gurkhas, 25,742 Army Reserve (United Kingdom), volunteer reserve perso ...
's Boxer network. In addition to the network itself, numerous additional Requirements followed for other parts of the system. ASR.894 described the network interface that would connect ICCS the UK's
Link 11 TADIL-A/Link 11 is a secure half-duplex tactical data link used by NATO to exchange digital data. It was originally developed by a joint committee including members from the Royal Canadian Navy, US Navy and Royal Navy to pass accurate targeting ...
being used by the Nimrod AEW3 aircraft. ASR.1585 called for transportable L-band radars, while ASR.1586 was a similar requirement for S-band systems. As had been the case in Linesman, widely separated bands would be used in order to make the jamming task more difficult. At the time, the system was to be delivered in five years, in September 1986, at an estimated price of US$240 million.


Construction

The L-band radar component was quickly awarded to the
Marconi Martello Martello is a family of phased array radar systems developed by Marconi Electronic Systems in the 1970s and introduced operationally in the early 1980s. They provided long-range early warning radar, early warning capabilities but also had the accu ...
system, a recently introduced design of some sophistication, while the NATO-funded sites would make use of the US-built
AN/TPS-59 The AN/FPS-117 is an L-band active electronically scanned array (AESA) 3-dimensional air search radar first produced by GE Aerospace in 1980 and now part of Lockheed Martin. The system offers instrumented detection at ranges on the order of and ...
in its GE592 guise. The selection of the corresponding S-band system was more contentious, with Plessey offering to merge their somewhat dated AR-3D receiver and display electronics with a new transmitter and antenna from
ITT-Gilfillan Gilfillan Brothers, later known as ITT-Gilfillan, was an American electronics company located in Los Angeles, best known for their radar systems. They changed names several times, and might be referred to as ITT Corporation Electronic Systems Radar ...
to produce the AR-320, which competed against the Hughes Air Defense Radar. Political wrangling, and Hughes' self-interest, delayed the selection for months, before it was ultimately won by the AR-320 based on hopes for additional export sales to NATO. The Martello systems had a relatively easy development and all four were delivered in 1986. The AR-320s were new, and the six systems were not delivered until 1988/89. By this time, the Nimrod AEW3 was running into significant problems. While the first example was delivered in March 1982, and the first production versions were delivered to No. 8 Squadron RAF in 1984, by this time the aircraft was already several years late and had missed its chance to be used in the
Falklands War The Falklands War () was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British Overseas Territories, British dependent territories in the South Atlantic: the Falkland Islands and Falkland Islands Dependenci ...
. Instead, No. 8 was flying surplus
Avro Shackleton The Avro Shackleton was a British long-range maritime patrol aircraft (MPA) which was used by the Royal Air Force (RAF) and the South African Air Force (SAAF). It was developed by Avro from their Lincoln bomber, which itself had been a developm ...
s hastily equipped for the AEW role using the electronics from the
Fairey Gannet The Fairey Gannet is a carrier-borne aircraft that was designed and produced by the British aircraft manufacturer the Fairey Aviation Company. It was developed for the Royal Navy, being the first fixed-wing aircraft to combine both the search an ...
. As the delays mounted, and with the ground radars already being delivered, in December 1986 the MoD cancelled the Nimrod in favour of the
Boeing E-3 Sentry The Boeing E-3 Sentry is an American airborne early warning and control (AEW&C) aircraft developed by Boeing. E-3s are commonly known as AWACS (Airborne Warning and Control System). Derived from the Boeing 707 airliner, it provides all-weathe ...
. This required the Shackletons to remain in service until the Sentries arrived. In 1987 the decision was made to add a passive tracking system for anti-jammer support. This had been an important part of the Linesman concept, where the Type 85 radars operated as one-half of two-station
triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle m ...
systems. With the Type 85s due to pass out of service with the commissioning of the AR-320s, a new system would be needed to fill this role. Additionally, a requirement for decoy transmitters was added, both to further confuse jammer systems as well as to provide multiple targets to
anti-radiation missile An anti-radiation missile (ARM) is a missile designed to detect and home in on an enemy radio emission source. Typically, these are designed for use against an enemy radar, although jammers and even radios used for communications can also be ta ...
s. Meanwhile, the TPS-592 radars, which should have been easily adapted from their US counterparts, ran into extensive delays due to the need to meet more stringent operational requirements, and ultimately took five years to pass tests. In late 1988, statements from one of the UKADGE members stated that the ICCS was "currently in the pre-technical transfer phase", with reports stating that it was far short of its requirements and could not be available before mid-1992. Other members of the consortium debated this and stated it would be available in 1990, but in April 1989 the MoD made it official and stated it was not expected to be fully operational until 1992. At least some of the problem was identified as the system using three different
programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
s,
CORAL Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...
, FORTRAN and
RTL/2 RTL/2 (Real-Time Language) is a discontinued high-level programming language for use in real-time computing, developed at Imperial Chemical Industries, Ltd. (ICI), by John Barnes (computer scientist), J.G.P. Barnes. It was originally used inter ...
, which led to a study into the feasibility of replacing all of these with the newly introduced
Ada Ada may refer to: Arts and entertainment * '' Ada or Ardor: A Family Chronicle'', a novel by Vladimir Nabokov Film and television * Ada, a character in 1991 movie '' Armour of God II: Operation Condor'' * '' Ada... A Way of Life'', a 2008 Bollywo ...
. This study concluded it would be extremely expensive and could only be contemplated as part of a mid-1990s mid-life upgrade. One of the key aspects of the system was the incorporation of data from airborne early warning aircraft. After considering several alternatives, the Nimrod AEW3 had been selected. Individual "blips" on the radars would be forwarded over the UK-developed
Link 11 TADIL-A/Link 11 is a secure half-duplex tactical data link used by NATO to exchange digital data. It was originally developed by a joint committee including members from the Royal Canadian Navy, US Navy and Royal Navy to pass accurate targeting ...
system to the CPRs, where they would be injected into the system as if they were data from any other radar. The blips would then be sent into the processors for track extraction. The system also needed to be able to receive data from the NATO AEW aircraft, also E-3 Sentry's, which used the new
JTIDS The Joint Tactical Information Distribution System (JTIDS) is an L band Distributed Time Division Multiple Access (DTDMA) network radio system used by the United States Department of Defense and their allies to support data communications needs, ...
communication system. The Sentry had onboard computer equipment which did track identification, forwarding only the processed tracks, not the individual "blips" on the radar screens. Under Project Cheek, formalized as Air Staff Requirement 894, a
Thorn-EMI Thorn EMI was a major British company involved in consumer electronics, music, defence and retail. Created when Thorn Electrical Industries merged with EMI in October 1979, it was listed on the London Stock Exchange and was once a constituent o ...
system would receive data from either aircraft and display it on a separate console. The operator would then copy data from the console into the main UKADGE consoles manually. With the cancellation of the Nimrod AEW, the UK also moved to the Sentry. In October 1989, the RAF announced it would be installing the JTIDS/
Link 16 Link 16 is a military tactical data link network used by NATO members and other nations, as allowed by the MIDS International Program Office (IPO). Its specification is part of the family of Tactical Data Links. Link 16 enables military aircra ...
system on their Sentry and Tornado aircraft, as well as their
air tanker Aerial firefighting, also known as waterbombing, is the use of aircraft and other aerial resources to combat wildfires. The types of aircraft used include fixed-wing aircraft and helicopters. Smokejumpers and rappellers are also classified a ...
fleet. The idea was that the tankers would be used as relay stations for the distant Tornado interceptors. Unfortunately, the existing ASR.894 design was not capable of relaying the number of messages this would require, and it was estimated this could not be added before 2005.


Delivery

By 1988, the system was already eighteen months behind schedule. All three key technologies of the system were missing; the Nimrod AEW had been cancelled, the ICCS didn't work, and Foxhunter radar for the interceptor version of the
Panavia Tornado The Panavia Tornado is a family of twin-engine, variable-sweep wing multi-role combat aircraft, jointly developed and manufactured by Italy, the United Kingdom and Germany. There are three primary #Variants, Tornado variants: the Tornado IDS ...
,
Tornado ADV The Panavia Tornado Air Defence Variant (ADV) is a long-range, twin-engine swing-wing interceptor aircraft developed by the European Panavia Aircraft GmbH consortium. It was a specialised derivative of the multirole Panavia Tornado. Developme ...
was non-functional. As had occurred with Linesman, chatter in government circles started about cancelling the system. Donald Spiers, the MoD's controller of aircraft, called for an internal audit of the programme. In June 1989, the MoD formed a new project known as TRIAD, short for Techniques for Realizing an Integrated Air Defence, in an effort to get the system up and running as quickly as possible. Plessey, Ferranti and Thorn-EMI all won contracts to study the idea of connecting new processors to the ICCS network through a public interface. Serious consideration was also given to simply cancelling the entire system outright, writing off the approximately $600 million US spent to date. It was at this time that Hughes sent in Nancy Price, a corporate troubleshooter, to get things moving again. She put the problems squarely on the organizational structure, "UKSL fought about whether it was my fault or your fault - we had to change the culture of the organization." Significant progress was seen in 1990 when deliveries of the Sentries began. The first arrived at
RAF Waddington Royal Air Force Waddington , commonly known as RAF Waddington, and informally known by its nickname 'Waddo' is a Royal Air Force station located beside the village of Waddington, south of Lincoln, Lincolnshire, in England. The station is th ...
on 4 July 1990, a month ahead of schedule, and the last in March 1992. Enough had arrived by June 1991 that the Shackletons were finally retired. A force of six active Sentries with another as a hot spare took over most of the air control duty. While the Sentries were arriving, the first all-up tests of the ICCS system were being carried out at the Sector Operations Centre at Buchan. These went relatively smoothly until they attempted to network other SOCs into the system, at which point all of the machines crashed. A key improvement was realized by replacing the now-outdated VAX 11/780 and 11/785 machines with the newer VAX 8650. The 8650, originally known as the 11/795, ran at 18 MHz rather than the 780's 5 or the 785's 7.5, offering well over twice the performance. Problems keeping the three sites in sync disappeared, along with the crashes, and this also allowed a reduction in the number of machines at each site. By the middle of 1991, the MoD was increasingly confident the system was finally ready for operation. Buchan SOC was handed over to the RAF on 27 September 1991. During early development, a backup site for Neatishead had been added to the original plans, whereas previously Boulmer had been the backup to both SOCs. After several abandoned bunkers from the ROTOR programme were examined, the complex from RAF Sandwich was selected and became the new
RAF Ash Royal Air Force Ash or more simply RAF Ash (formerly RAF Sandwich) was a Royal Air Force underground control centre and radar station situated near the village of Woodnesborough, Kent, England. History RAF Sandwich RAF Sandwich was origina ...
. Construction work to enlarge the bunker began in 1984. This also became the Operational Conversion Unit (OCU) for radar operators migrating from Linesman to UKADGE. It operated in this role until 1 October 1993, when the School of Fighter Control moved from
RAF West Drayton RAF West Drayton was a non-flying Royal Air Force station in West Drayton, within the London Borough of Hillingdon, which served as the main centre for military air traffic control in the United Kingdom. It was co-located with the civilian Lon ...
to Boulmer and the OCU moved with it. Ultimately Ash was never used as an operational UKADGE SOC, and the bunker was left half-converted with much of its equipment abandoned in a pile at the site. Ash closed in 1995 and was later sold. Extensive remedial changes to the software of the ICCS continued and a major update was officially delivered in September 1992. The other SOCs and CRCs followed, and the entire system was declared fully operational on 1 June 1993, "a mere six years behind schedule". The MoD credited the final competition of the system to Price, who went on to become the president of Hughes Canada, building the Canadian Automated Air Traffic System. By the time the system was complete, US$1.6 billion had been spent, against initial estimates of US$240 million. Ultimately about half of the funding came from the NATO pool, including 80% of the cost of the radars.


History repeats

By the time the system was finally delivered, IUKADGE was seen as obsolete. The
Warsaw Pact The Warsaw Pact (WP), formally the Treaty of Friendship, Co-operation and Mutual Assistance (TFCMA), was a Collective security#Collective defense, collective defense treaty signed in Warsaw, Polish People's Republic, Poland, between the Sovi ...
had been falling apart through the late 1980s, and in 1991 the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
officially ceased to exist. As the Russian economy faltered, the number of intruder flights plummeted, from about five a week in 1980, to zero. The system, designed to track long-range, low-flying aircraft and their
cruise missile A cruise missile is an unmanned self-propelled guided missile that sustains flight through aerodynamic lift for most of its flight path. Cruise missiles are designed to deliver a large payload over long distances with high precision. Modern cru ...
weapons, no longer had a credible target. Addressing even an all-out attack would require a system much less extensive than IUKADGE, and the need for significant redundancy no longer seemed pressing. Moreover, many of the systems used in the ICCS, notably the VAX computers, were no longer available. These machines, which filled small rooms, had been replaced by ever-smaller systems, and eventually by emulators running on desktop platforms. The networking systems of ICCS, which initially required entire computers of their own, could now be implemented in small boxes, while the underlying network system was being outperformed by commercial networks that could be purchased over the counter.


Replacement

While the system was being brought up, there were already discussions about its future. The UKSL consortium members were invited to submit bids on maintaining the systems, either individually or as the UKSL group. The MoD eventually decided to abandon the UKSL given its poor performance before the arrival of Price, who had since left. In the meantime, in January 1993 bids were taken to replace the GE592 systems, which was awarded to Plessey in 1994 with a further updated version of the AR-320, the AR-327. In June 1996 the MoD announced the IUKADGE system would be replaced outright. This was formalized in Staff Requirement (Air) 1303, which called for a single
Joint Force Air Component Headquarters The Joint Force Air Component Headquarters (JFACHQ) is the United Kingdom's deployable air command and control unit. The JFACHQ is run by the Royal Air Force with representation from the other services. The JFACHQ has members from the operat ...
that would run the RAF in both the UK and also be deployable overseas, and a separate Tactical Air Control Centre to direct fighter operations. The JFAC was estimated to be running by 1998 and the entire system by 2003. This programme also ran into significant delays, this time mostly due to a lack of interest as Russian activity remained low. It eventually emerged as the
Air Surveillance and Control System An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...
(ASACS).


Description

The main portion of the UKADGE network consisted of a group of transportable radar systems and a computer network to transmit data between them. From north to south, the radar stations were: *
Sornfelli Sornfelli is a mountain plateau on the island of Streymoy in the Faroe Islands about 12 km from the capital Tórshavn (20 km by road). It is the site of a military station at 725m above sea level (asl). The Sornfelli Meteorological Stat ...
, on
Streymoy Streymoy (, ) is the largest and most populated island of the Faroe Islands. The capital, Tórshavn, is located on its southeast coast. The name means "island of currents". It also refers to the largest region of the country that also includes the ...
in the
Faroe Islands The Faroe Islands ( ) (alt. the Faroes) are an archipelago in the North Atlantic Ocean and an autonomous territory of the Danish Realm, Kingdom of Denmark. Located between Iceland, Norway, and the United Kingdom, the islands have a populat ...
operated by
Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...
as part of NATO *
RAF Saxa Vord Remote Radar Head Saxa Vord or RRH Saxa Vord (aka RAF Saxa Vord), is a Royal Air Force radar station located on the island of Unst, the most northern of the Shetland Islands in Scotland. As of July 2019 it is once more a fully operational radar ...
in the
Shetland Islands Shetland (until 1975 spelled Zetland), also called the Shetland Islands, is an archipelago in Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the Uni ...
* RAF Benbecula in the
Outer Hebrides The Outer Hebrides ( ) or Western Isles ( , or ), sometimes known as the Long Isle or Long Island (), is an Archipelago, island chain off the west coast of mainland Scotland. It is the longest archipelago in the British Isles. The islan ...
*
RAF Buchan Remote Radar Head Buchan or RRH Buchan is an air defence radar station operated by the Royal Air Force. It is located at Stirling Hill, south of Peterhead on the Aberdeenshire coast of northeast Scotland. The unit is based at the operations sit ...
in
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
, which was also the northern sector SOC *
RAF Boulmer Royal Air Force Boulmer or more simply RAF Boulmer is a Royal Air Force station near Alnwick in Northumberland, England, and is home to Aerospace Surveillance and Control System (ASACS) Force Command, Control and Reporting Centre (CRC) Boulmer ...
in
Northumberland Northumberland ( ) is a ceremonial counties of England, ceremonial county in North East England, on the Anglo-Scottish border, border with Scotland. It is bordered by the North Sea to the east, Tyne and Wear and County Durham to the south, Cumb ...
* RAF Bishops Court in
Northern Ireland Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...
*
RAF Staxton Wold Remote Radar Head Staxton Wold or RRH Staxton Wold is an air defence radar station operated by the Royal Air Force, located near Scarborough in North Yorkshire, England. As it has been a radar site continuously since 1939, it has a claim to be t ...
in
Yorkshire Yorkshire ( ) is an area of Northern England which was History of Yorkshire, historically a county. Despite no longer being used for administration, Yorkshire retains a strong regional identity. The county was named after its county town, the ...
, downgraded to a radar station only *
RAF Neatishead Remote Radar Head Neatishead ( ), and commonly abbreviated RRH Neatishead, is an air defence radar site operated by the Royal Air Force (RAF). It is located approximately north-east of Norwich in the county of Norfolk, England. Originally kno ...
in
Norfolk Norfolk ( ) is a Ceremonial counties of England, ceremonial county in England, located in East Anglia and officially part of the East of England region. It borders Lincolnshire and The Wash to the north-west, the North Sea to the north and eas ...
, the southern sector SOC *
RAF Portreath Remote Radar Head Portreath or RRH Portreath is an air defence radar station operated by the Royal Air Force. It has a coastal location at Nancekuke Common, approximately north east of the village of Portreath in Cornwall, England. Its radar ( ...
in
Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...
In addition to the radar stations, several other stations were included: *
RAF High Wycombe Royal Air Force High Wycombe or more simply RAF High Wycombe is a Royal Air Force station, situated in the village of Walters Ash, near High Wycombe in Buckinghamshire, England. It houses Headquarters Air Command, and was originally designed ...
,
RAF Strike Command The Royal Air Force's Strike Command was the military formation which controlled the majority of the United Kingdom's bomber and fighter aircraft from 1968 until 2007 when it merged with Personnel and Training Command to form the single Air ...
headquarters, hosted the Air Defence Operations Centre *
RAF Bentley Priory RAF Bentley Priory was a non-flying Royal Air Force station near Stanmore in the London Borough of Harrow. It was the headquarters of Fighter Command in the Battle of Britain and throughout the Second World War. The Royal Air Force station c ...
,
Royal Observer Corps The Royal Observer Corps (ROC) was a civil defence organisation intended for the visual detection, identification, tracking and reporting of aircraft over Great Britain. It operated in the United Kingdom between 29 October 1925 and 31 Decembe ...
headquarters, was the Standby ADOC *
RAF Ash Royal Air Force Ash or more simply RAF Ash (formerly RAF Sandwich) was a Royal Air Force underground control centre and radar station situated near the village of Woodnesborough, Kent, England. History RAF Sandwich RAF Sandwich was origina ...
was the backup southern sector control, but never operated in that role *
RAF West Drayton RAF West Drayton was a non-flying Royal Air Force station in West Drayton, within the London Borough of Hillingdon, which served as the main centre for military air traffic control in the United Kingdom. It was co-located with the civilian Lon ...
, the former L1 of Linesman, remained in use as the military air traffic control centre (ETF) UKADGE was linked to a number of similar networks as well. These included: * NADGE at Glons, Nieuw Milligen, Vedbaek, Maakeroy, Graakallen and Reitan * STRIDA II in Tours and Doullens *
Link 11 TADIL-A/Link 11 is a secure half-duplex tactical data link used by NATO to exchange digital data. It was originally developed by a joint committee including members from the Royal Canadian Navy, US Navy and Royal Navy to pass accurate targeting ...
and
Link 16 Link 16 is a military tactical data link network used by NATO members and other nations, as allowed by the MIDS International Program Office (IPO). Its specification is part of the family of Tactical Data Links. Link 16 enables military aircra ...
connections to AEW aircraft and Royal Navy ships A total of twelve ground radars were purchased as part of the network. These included four Martello S723s, known as AMES Type 91 in the RAF's radar numbering scheme, two GE592 as Type 92, and six AR320 as Type 93. The GE592s were used at Boulmer and Benbecula.


Notes


References


Citations


Bibliography

* * * * * * * * * * * * * *


Further reading

* * * {{cite magazine , first=Mark , last=Hewish , title=Britain's air defences grow new teeth , magazine=New Scientist , date=12 March 1981 , pages=682–684 , url=https://books.google.com/books?id=x57gHRJjGC4C&pg=PA682 Air defence radar networks Military equipment of the United Kingdom