Improved United Kingdom Air Defence Ground Environment
The Improved United Kingdom Air Defence Ground Environment, normally shortened to either UKADGE or IUKADGE, was the Royal Air Force's ground-controlled interception system covering the British Isles during the 1990s. It consisted of a number of ground-based radar sites, links to airborne early warning aircraft and Royal Navy ships, a telecommunications system to send digital data and voice communications on a protected network, and processing systems based on VAX-11/780 computers. The network ultimately contained a dozen long-range radars including four Marconi Martello, two General Electric TPS-592, and six Plessey AR-320.
UKADGE was developed in response to concerns about its predecessor, Linesman/Mediator. Linesman started in the 1950s, when it was assumed that any air attack on the UK would be by hydrogen bomb 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 reaching strategic parity with NATO, 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 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 jammers, several new radars were introduced that operated across a wide band of frequencies from L to S. 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 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 won a contract to rebuild the command and communications portions of the system, which emerged as the current Air Surveillance and Control System, which is in the process of being replaced by the new Project Guardian.
History
Defence in the nuclear era
In 1957, Duncan Sandys introduced his Defence White Paper which, among other topics, considered the effect of the introduction of ballistic missiles 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 force had to be able to launch with extreme rapidity.At the time, the Royal Air Force 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 radars, using fewer but longer-ranged radars. The main goal was to counter the carcinotron 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 plans, targets separated out, and directions sent to the interceptor aircraft. 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 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 agreed to move one of their new BMEWS radars to the UK, initially to Scotland, but later to Yorkshire at RAF Fylingdales 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 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 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 bombs, 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, whose previous experience in telephone switching left them unprepared for the level of programming support needed. Eventually, programmers from the Atomic Weapons Research Establishment 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 assumed a tripwire force concept where conventional forces were not expected to actually stop Warsaw Pact forces. Instead, any attack on these forces would be responded to with tactical nuclear weapons against the Pact forces and high-value targets. If this failed to stop the war, a "massive retaliation" using strategic weapons would be launched against the USSR. NATO's massive air superiority ensured the attack would succeed.In July 1964, the US Joint Chiefs of Staff 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 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 Marshal Sir 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 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 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 display, using it to frequency modulate a microwave signal, and then sending the resulting signal to L1 using wideband microwave relays. 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, 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 with a greater number of simpler and cheaper systems.