Chapter Twelve










Display performance to the highest possible quality is essential to any radar system. The first radar system that the Decca Company produced was the 159 which employed an antenna that was static until manually steered via a Bowden Cable. The radar’s returned signal was presented on an ‘A-Scope’ with distance on the ‘X’ axis and target amplitude on the ‘Y’ axis. By the time the 159 (B) went into production the antenna was continuously driven through 360degrees by an electric motor. The returned signals (echoes) were then displayed on a 9inch PPI (Plan Position Indicator). The time-base was swept by a set of deflection coils on the neck of the cathode-ray-tube, which were driven, in sync with the antenna rotation, by a motor of the type used in the parent Company’s gramophones.

In 1952 a small team of engineers within the ‘Radar Research Lab’, under the management of S.R. Tanner and the leadership of Bob Matthews, was formed to design a fixed coil radar display (FCD). It would eliminate the need for deflection coils to be motor driven.

By Christmas 1952 a prototype display was giving encouraging results. The antenna representation could be moved from the centre of the tube and this ‘off-centering’ demonstrated clearly the displays potential use as an HRI (Height Range Indicator).

From this point in time however, the development of displays was to take a dual path within the Decca Radar Company. The rotating coil display would remain favoured for Marine Radars, where they were aimed at use on smaller sea-going vessels, but for larger ships and land based applications the Fixed Coil Display became the norm.

The following pages trace the progressive development of displays from 1949. Also recorded here is how the demise of the Addlestone based Display and Signal Processing Group was accommodated by the radar company operating from both Chessington in Surrey and Cowes on the Isle of Wight.

When the Addlestone display design and manufacturing unit was no longer integrated with the radar company, the Siemens/Plessey operation at Chessington took their display procurement onto a different path. The ‘jargon’ would no longer refer to ‘Displays’, they became CRT Monitors, and these were available from hotly competing specialists such as Sony, Ricard Miller and Barco.

Finally, with computers and computer monitors available on the open market and with the digitised processing of most radar outputs, the thrust changed to systems designed with screen projection, bright displays and those of a raster-scan technology. Raster scan (TV style) displays became available from the supply market and therefore ‘in house’ display development ceased.


Mk.6 FCD never reached production and only a limited number of Mk.7’s, a specialist touch control and tabular display, were supplied to the market (mainly EURO CONTROL).

1961, the year of the transistorised Fixed Coil Display, representing a major milestone in display development. It had a shift time of 100 microseconds and with character writing at 200 microseconds (extremely fast compared with its thermionic valve predecessors). Many hundreds of the Mk.5 were made to typically function in conjunction with the HF200 (PPI and HRI) and the AR-1 where there were 3 operational displays and sometimes a monitor in the Transmitter Room.

Mk.6 FCD never reached production and only a limited number of Mk.7’s, a specialist touch control and tabular display, were supplied to the market (mainly EURO CONTROL).

12.3. DATA PROCESSING SYSTEMS - (Command & Control/Operation Rooms)

Those that can recall the WW2 years may reflect on an Operations Room that had young ladies moving wooden tallies, representing aircraft, around a plotting table, housed within a noisy environment.

Picture of operation room

As radar displays developed, both PPI and HRI had the added ability to present text, so the Operations Room character changed. 360degree surveillance would be divided into sectors each with its own display and operator. Any changes in the observed situation would be electronically filtered and carried forward to the next level of Controller. (The silence could now be almost oppressive). Computers with pre-loaded profiles of any potential targets would be linked to automated weapon systems. Displays and other such sub-system elements would be hung onto a signal or information digital highway (ring main style).

It was probably the work carried out by Decca Radar at Hersham in 1956, on a digital computer project (‘Mervyn’), that proved the feasibility of using a digital computer to aid aircraft tracking.

In 1956, (at Tolworth) the project ‘Conrad’ addressed the first customer need to network a series of fixed coil displays. This has since been recognised as the root of all Decca/Plessey digitally based control systems as those programmers/analysts formed the nucleus of future design teams. The ‘What’ and ‘How’ are too complex to record at length, but the following lists some of the control system designs undertaken for Maritime, Air Defence and Civil Air Traffic Control, by the ‘Addlestone’ based team.


Harbour Radar Surveillance Display System. The early 16-inch analogue Mk.4 display system was designed at Tolworth and Hersham for Southampton, Liverpool, Port of London Authority, Hamburg and Khandla (India).


1956 – Konrad was a display system equipment for the German Defence Forces.

Late 1950s – Mk. 4 displays, from Tolworth were used as Height Range Indicators (HRI’s) for the HF 200 height-finding radars. In later systems Mk. 5 displays were used. This was associated with HF 200 ‘Azication’ control systems from the Heavy Radar team at Davis Road. These were supplied to MOD/RAF stations, Sweden and Finland (FDF).

Early 1960s – Project ‘Marilyn’ provided Mk. 5 displays and liquid cooled display drive systems, with automatic tracking, intercept control and threat evaluation, to Finland.

Mid 1960s – Project ‘Hubcap’ - An Intercept control/threat evaluation system for the Royal Australian Air Force; comprising a digital computer based Control and Reporting System (CRUS) using Mk.5 displays.

Late 1960s – The ‘Linesman/Mediator’ Project provided joint Civil/Military display systems to the MOD for the management of the UK’s airspace.

1980s - Project ‘Rodent’ - Containerised Air Defence display systems from Chessington for the South African Air Force functioning with the AR-3D Radars from Cowes. GL161 - Air Defence Display Systems for the U.K. MOD. GL161 was the first successful application of automatic data processing (ADP) for the calculation of intercept profiles and aircraft recovery in RAF service – probably a world first.

UKADGE – A system to integrate outputs from Military and Civil Radars throughout the UK.


Early 1960s - An ATC system for Zurich and Geneva Airports embracing surveillance and control. Analogue Mk.4 displays with an automatic tracking system, target symbology and video map.

1963-66 Bretigny Simulator Project. A digital computer based ATC simulator supplied to the European Organisation for the safety of Air Navigation (Eurocontrol). Developed at the Operational Research Centre, Bretigny, France. The project was undertaken by a consortium of companies, CSF (France), Telefunken (Germany) and Decca/Plessey. Decca/Plessey were to address the ‘man machine interface’ comprising a large number of Mk.5 displays and associated programmable controller keyboards. Many Mk.7 displays with ‘touch screen inputs’, for pilot position use and a large screen projection display formed part of the system. The digital development work previously carried out at Hersham was used to good effect when interconnecting the man-machine interface with the main computer.

1967 saw a CAA/NATS contract for the enhancement of the integrated display of UK radar outputs installed at West Drayton.

1970 a Data Processing and Display System was developed for the Heathrow Tower/Approach Control. The customer was again CAA/NATS.

1969-73 MADAP (Maastricht) – a project for Eurocontrol for an ATC system to control all aircraft in the Upper Air Space over Belgium, Holland, Luxemburg and Northern Germany. Plessey as part of a consortium provided both the system design and project management. The main processing, comprising three IBM360/50 digital computers was the responsibility of Plessey Radar. The Company also provided a large number of analyst/programmers to design and produce both system and operational software.

1972 Plessey Radar were contracted to design and install a regional sub-centre, based on the Manchester area, to support the CAA/NATS control centre functioning at West Drayton (London).

1975 The team at Addlestone addressed a contract to update the data processing system at London’s Air-Traffic Control Centre (PRDS).

1978-82 An ATC system was to be designed for Vienna, this followed by a succession of additions and updates. The system would be used to control all Air Traffic within the air space of the Republic of Austria. The system had a triplicate main processing system using DEC Computers with automatic changeover. The main processing system performed full multi radar tracking from six remote radars with full flight plan processing. The man machine interface comprised a large number of consoles each with their own local computer and colour display. The system has a reputation of being one of the most reliable within its field of operation.(The good customer/supplier relationship led to update contracts through to 1997).

1978-83 (and then again 1986-89) – Project TIINA – A project for Finland, which comprised 8 Watchman Radars each with operator display consoles for joint civil/military use, providing Approach Control and Fighter Recovery at individual airfields and centralised integration of the eight radar outputs.

1978-84, Project PARAKEET. A project for Indonesia. It was for the modernization and upgrading of the Air Defence Centres supplied by Decca under the ‘Parrot’ project, this also included the upgrading of a number of Russian Radars.

1994 saw work being carried out to design and supply an ATC Control Centre for Sweden. (S2000) 1998 also saw work being carried out to design and supply an ATC Control Centre for Hungary. (Project MATHYAS)

Picture of Typical 1980’s configuration of a land based Control Centre.

Picture of Typical 1980’s configuration of a Seagoing Control Centre.


Finland’s Defence Scheme of the 1950’s The system was initially based on Mk. IV displays with their thermionic valve technology (note the valve cooling ducted air tubes in the ‘wall frame unit’ picture). At a later date the system was upgraded to employ Mk. V ‘Transistorised’ displays.

Typically the operational sequence involved the detection of a probable target on the sector ‘Tracking Display’, extracts would then be passed up to senior staff at the ‘Conference Display’ from where authority would be passed to operators at the ‘Intercept control Console’.


Picture of Mk. V Intercept Control Console.

Picture of 21” Conference Display,  Mk. IV Display Drive Wall Frames and Mk. IV Tracking Display.

Picture of Mk. IV Tracking Display.

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