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{{short description|British electronics, defence and telecommunications company}}
{{about|the British company|the decision by the United States Supreme Court|Plessy v. Ferguson{{!}}''Plessy v. Ferguson''}}
{{EngvarB|date=April 2018}}
{{Use dmy dates|date=May 2020}}
{{Infobox company
| name = Plessey
| logo = Plesseylogo.jpg
| type = Public company
| caption = 
| fate = Acquired <br> <small>(in 1989 by GEC/Siemens joint holding company – GEC Siemens)</small>
| successor = [[General Electric Company|GEC]]<br><small>(1989–1999)</small><br>[[Siemens Plessey]]<br><small>(1989–1997)</small><br>[[Marconi Communications]]<br><small>(1998–2006)</small><br>[[Siemens Communications]]<br><small>(1998–2006)</small><br>[[BAE Systems]]<br><small>(1999 till date)</small><br>Plessey Semiconductors<br><small>(2010 till date)</small>
| foundation = 1917
| defunct = 1989
| location = [[Ilford]], Greater London, England
| industry = [[Electronics]], [[Defense (military)|defence]] and [[telecommunications]]
| key_people = [[John Allen Clark|Sir John Clark]] (chairman)
| products = 
| num_employees = 
| parent = 
| subsid = 
}}

'''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 companies. It was listed on the [[London Stock Exchange]] and was a constituent of the [[FTSE 100 Index]]. In 1989, it was taken over by a consortium formed by [[General Electric Company|GEC]] and [[Siemens]] which split the assets of the Plessey group.

The majority of Plessey's defence assets were amalgamated into [[BAE Systems]] in 1999 when [[British Aerospace]] merged with the defence arm of GEC, [[Marconi Electronic Systems]] (MES). The Plessey Microsystems division was the subject of a management buyout in 1988<ref>{{Cite book |url=https://archive.org/details/bitsavers_ComputerDe27N1519880815_72508955 |title=Computer Design |date=August 1988 |year= |pages=49 |language=en}}</ref><ref>{{cite web |title=VME BOARD BUILDER PLESSEY MICROSYSTEMS BECOMES RADSTONE IN MANAGEMENT BUYOUT |url=https://techmonitor.ai/technology/vme_board_builder_plessey_microsystems_becomes_radstone_in_management_buyout |website=Techmonitor |date=26 May 1988 |access-date=30 October 2023}}</ref> becoming [[Radstone Technology]], which survives today as part of [[Abaco Systems]] based in [[Towcester]], [[Northamptonshire]]. The bulk of Plessey's telecommunications assets were acquired by [[Ericsson]] through its 2005 acquisition of [[Marconi Communications]], a successor company of GEC.

==History==
===Early history===
The Plessey company was founded in 1917 in [[Marylebone]], central London. The original shareholders were Thomas Hurst Hodgson, C. H. Whitaker, Raymond Parker and his brother Plessey Parker.<ref name = history>{{cite web |title=A résumé of the history of Plessey, compiled by Hugh Culverhouse, a nephew of Sir Allen Clark |url=https://sites.google.com/site/plesseyaddlestonereunion/plessey-company-history |access-date=4 April 2012 |archive-date=26 April 2014 |archive-url=https://web.archive.org/web/20140426235847/https://sites.google.com/site/plesseyaddlestonereunion/plessey-company-history |url-status=live }}</ref> A talented German engineer, William Oscar Heyne, was employed by the company. Heyne later became the managing director and chairman of Plessey and was one of the key figures in the development of Plessey during the 1920s and 1930s.<ref name=history/> The company moved to Cottenham Road in [[Ilford]] early in 1919.<ref name=history/> In 1925, the original company was wound up and a new one was formed with a greater share capital. Most of the early work carried out by the company was in mechanical engineering.

===The Clark connection===
An early customer of Plessey was a [[galvanising]] company called British Electro Chemists. One of that company's shareholders was Byron G. Clark, an American, who was also a business associate of T. H. Hodgson, one of the founders of Plessey. The Clark family would eventually dominate the management of Plessey for most of its history. Byron's son [[Allen George Clark]] joined the company in 1921, and went on to become a driving force behind the development of Plessey,<ref name=history/> followed later by his sons [[John Allen Clark]], and Michael William Clark,<ref>{{cite news |title=Michael Clark |url=https://www.telegraph.co.uk/news/obituaries/finance-obituaries/7937403/Michael-Clark.html |work=[[The Daily Telegraph]] |location=London |date=10 August 2010 |access-date=2 April 2018 |archive-date=1 March 2018 |archive-url=https://web.archive.org/web/20180301044541/https://www.telegraph.co.uk/news/obituaries/finance-obituaries/7937403/Michael-Clark.html |url-status=live }}</ref> both of whom rose to prominent positions in the company.

===Electrical manufacturing===
During the 1920s Plessey began to diversify into electrical manufacturing. Important contracts included the manufacture of early radios<ref name=history/> for [[Marconi Company|Marconi]] and the production of telephones for the [[General Post Office]]. In order to increase production, Plessey moved to Vicarage Lane, [[Ilford]], in 1923.<ref name=history/> In 1929, the television pioneer [[John Logie Baird]] had his first production televisions made by Plessey.<ref name=history/> The company also produced the first British-made portable radio in the same year.

The manufacture of electrical components became an area of growth for Plessey. A vast array of components was manufactured, many under licence from overseas companies. Plessey became one of the largest manufacturers in this field as the radio and television industries grew. In 1936/7, turnover was more than £1&nbsp;million and Plessey became a public company on 17 March 1937.

===Aircraft components===
Aircraft components was another market into which the company diversified. In 1936, Plessey obtained a number of important manufacturing licences from American companies such as Breeze Corporation for aircraft multi-pin [[electrical connectors]], Federal Laboratories for [[Coffman starter]]s (an explosive cartridge device used to start aircraft engines), and Pump Engineering Services Corporation for the manufacture of Pesco [[Fuel pump (engine)|fuel pumps]]. Plessey went on to produce large numbers of these fuel pumps for [[Rolls-Royce Merlin]] engines, and in 1940 the fuel pump for Britain's first jet engine was also supplied by Plessey.

[[Image:R1155 Receiver and T1154 Transmitter at RAF Digby.jpg|thumb|upright|[[R1155]] receiver on top of T1154 transmitter]]

===World War II===
During [[World War II]], Plessey produced a vast array of components and equipment for the war effort, including shell cases, aircraft parts, and radio equipment such as the [[R1155]] (receiver), and T1154 (transmitter). In all, 161,500 pieces of wartime electronic equipment were produced.

To allow greater production, Plessey converted five miles of twin tunnel, built for a [[Fairlop Loop|new extension]] to the [[London Underground]] [[Central line (London Underground)|Central line]] from [[Leytonstone tube station|Leytonstone]] to [[Newbury Park tube station|Newbury Park]], into a factory.<ref name=history/> The company also built a new factory at [[Swindon]] in Wiltshire, and opened several other shadow factories around the country to produce munitions. [[Plessey Research Caswell|Caswell]], Northamptonshire became the site of Plessey's first dedicated research centre in 1940. The wartime workforce of Plessey grew to over 10,000.

===Post World War II===
With the end of the war the company's orders dropped from £5&nbsp;million in 1944/5 to £263,000 in 1946 and the workforce fell to less than 6,000. Radio and television sales were the main area of activity until the renewed demand for defence products with the onset of the [[Korean War]]. From a turnover of £5&nbsp;million in 1949/50, there was an increase to £32&nbsp;million in 1959/60.

In 1951, the Electronics Division was started by Michael Clark. By 1955, this had expanded to become the Electronics and Equipment Group with 5,000 staff. The following year the [[Roke Manor]] research facility was set up under the direction of H. J. Finden near [[Romsey]], Hampshire. Plessey produced an early [[integrated circuit]] model in 1957, before the patents of [[Jack St. Clair Kilby]] of [[Texas Instruments]] and [[Robert Noyce]] of Fairchild.<ref>{{cite book |last1=Morris |first1=Peter Robin |title=A History of the World Semiconductor Industry |date=30 June 1990 |publisher=The Institution of Engineering and Technology |isbn=9780863412271 |pages=184}}</ref><ref>{{cite web|url=http://www.electronicsweekly.com/blogs/david-manners-semiconductor-blog/2008/09/50th-anniversary-of-the-ic.html|title=50th Anniversary of the IC|author=David Manners |work=ElectronicsWeekly|date=12 September 2008|access-date=30 April 2009|archive-date=9 January 2009|archive-url=https://web.archive.org/web/20090109143406/http://www.electronicsweekly.com/blogs/david-manners-semiconductor-blog/2008/09/50th-anniversary-of-the-ic.html|url-status=live}}</ref><ref>{{cite journal |last1=Duncan |first1=Helen |title=This is Your Life: Caswell Research Centre |url=https://www.newelectronics.co.uk/content/features/this-is-your-life |journal=New Electronics |date=9 March 2009}}</ref> In the 1960s the Group continued to expand, setting up facilities at places such as West Leigh ([[Havant]], Hampshire) and [[Templecombe]], Somerset.
[[Image:Plessey.png|thumb|Plessey Electronics logo]]
In 1961 Plessey merged with [[Ericsson Telephones]] and [[Automatic Telephone Manufacturing Company]] of Liverpool, to become Britain's largest manufacturer of [[telecommunications]] equipment, including the majority of the country's [[crossbar switch]]es.<ref name=history/> Alongside the Telecommunications Division, three other businesses were set up: Plessey Avionics and Communications, Plessey Radar and Plessey Marine. In 1967 or 1968, [[English Electric]] was subject to a takeover bid by Plessey, but chose instead to accept an offer from [[General Electric Company|GEC]]. In 1970, the Command and Control unit was set up at [[Christchurch, Dorset]], which became the centre of the Plessey Defence Systems business. In 1979, a major subsidiary was set up, Plessey Electronic Systems, which incorporated the three businesses and by 1986 achieved sales of over £500 million and employed 15,000.

Plessey were partners in the development of the [[Atlas Computer]] in 1962 and in the development of digital telephone systems, including [[System X (telephony)|System X]], from the late 1970s.<ref name=history/> In 1988, Plessey's Telecommunications Division merged with that of GEC to become [[GEC Plessey Telecommunications]]. Plessey Naval Systems was formed in 1986 by the merger of Plessey Marine with Plessey Displays, which had been part of Plessey Radar. Plessey were among the first firms to use computers. Their Training Department developed an interactive management game (PITDEX) using [[TeleType]] printer/keyboards to link to LEASCO computers in the United States via standard telephones and [[acoustic coupler]]s.[[File:Fixed Survey Meter PDRM82F.jpeg|thumb|Plessey PDRM82F geiger counter]]

Plessey also pioneered the gathering and consolidation of accounting information from around the world using in-house software. Each of their 140 management reporting entities used HP125s with DIVAT (data input, validation and transmission) software. Nearly 450 validation rules ensured accuracy within and between various reports. The data were then transmitted to [[Ilford]] where a [[HP 3000]] ran [[Fortran]] software for consolidation and reporting—also on HP125s.<ref>Micro Decision, August 1983; Accountancy, March 1984; Information Systems. February 1986</ref> By 1972, Plessey designed the first industrial [[capability-based security]] computer, a fault-tolerant multiprocessor system called [[Plessey System 250]]. Plessey was also the lead contractor for the [[British Armed Forces communications and information systems#Ptarmigan (telecommunications)|Ptarmigan]] communications system supplied to the [[British Army]], which adopted the System 250 architecture.<ref name="history" />

A division focused on microcomputing, Plessey Microsystems, was founded in 1975, having licensed the 16-bit Miproc processor architecture developed by the [[Norwegian Defence Research Establishment]] and Aksjeselskapet Mikro-Elektronikk.<ref name="microcomputerdigest197508_plessey">{{ cite magazine | url=https://archive.org/details/bitsavers_microcompuomputerDigestv02n02Aug75_2112666/mode/2up | title=British Firm Steps Up µC Efforts | magazine=Microcomputer Digest | date=August 1975 | access-date=9 February 2024 | pages=1,4 }}</ref> In contrast to the existing implementation, announced with a 200ns cycle time,<ref name="electronicdesign19740510_aker">{{ cite magazine | url=https://archive.org/details/bitsavers_ElectronicignV22N1019740510_127749588/page/176/mode/1up | title=Compact processor has 5-MHz instruction rate | magazine=Electronic Design | date=10 May 1974 | access-date=9 February 2025 | pages=176 }}</ref> Plessey introduced Miproc with a 350ns cycle time as part of a development system costing ${{Format price|5000}}.<ref name="computerworld19751224_plessey">{{ cite magazine | url=https://archive.org/details/computerworld952unse/page/15/mode/1up | title=Plessey Has 16-Bit Micro With 350 Nsec Cycle Time | magazine=Computerworld | date=24 December 1975 | access-date=9 February 2025 | pages=15 }}</ref> During the 1970s and early 1980s, Plessey manufactured a series of computer systems and peripherals compatible with [[Digital Equipment Corporation]]'s [[PDP-11]], some based on the Miproc product which was itself revised to operate with a faster 250ns cycle time.<ref name="computerworld19800428_plessey">{{ cite magazine | url=https://archive.org/details/sim_computerworld_1980-04-28_14_17/page/68/mode/1up | title=Plessey’s Associate Processor Reconfigured for DEC PDP-11s | magazine=Computerworld | date=28 April 1980 | access-date=9 February 2025 | pages=68 }}</ref> The company would eventually expand its Miproc range to include the Miproc RTS, running the RTX real-time operating system, alongside Plessey's other product lines featuring semiconductor and bubble memory, and microprocessor-based data terminals.<ref name="compec1981">{{ cite book | url=https://archive.org/details/compec81officialcatalogue/Compec%20%2781%20Official%20Catalogue%20-%20Compressed/page/n71/mode/1up | title=Compec '81 | publisher=Computer Weekly | date=1981 | access-date=9 February 2025 | pages=137 }}</ref>

Plessey Controls, from 1982 to the mid-1980s, also manufactured a type of geiger counter known as the Portable Dose Rate Meter (PDRM). It gave highly accurate readings, using the Gray system of measurement and used standard torch batteries. They were built for civil defence, but also used by the British Army. Most ended up in the hands of the Royal Observer Corps and manufacture would discontinue by the late 1980s.

===UK air defence===
In 1959 AT&E, later Plessey, became the prime contractor for a new UK air defence system, known by the company under the name Plan Ahead and, from 1961, as [[Linesman/Mediator|Project Linesman]].<ref name=radar>{{Cite web|url=http://www.radarpages.co.uk/download/p172.pdf|title=40 years of Marconi Radar 1946 to 1986|access-date=27 December 2008|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304001730/http://www.radarpages.co.uk/download/p172.pdf|url-status=live}}</ref> To enable the system to be designed and built without too much information becoming public knowledge, a new factory called "Exchange Works" was built in Cheapside in Liverpool city centre, where young employees were granted exemption from conscription.

At the heart of the system, installed in a huge building in the middle of a council housing estate in [[West Drayton]], was the computer room, occupying an area of around {{convert|300|x|150|ft}} and filled with around 1,000 {{convert|7|ft|m|adj=mid|-high}} racks of electronics, including mainly the XL4 computer, based entirely on germanium transistors and using a computer language developed at Exchange Works in the 1950s and 1960s.<ref name=radar/> The secure status of the factory attracted many other secret contracts and led to it becoming one of the major designers and manufacturers of cryptographic equipment. Exchange Works is now luxury flats.

===South Africa===
The South African roots of Plessey can be traced to the acquisition of AT&E and Ericsson in 1963, and a [[Cape Town]] based company, the Instrument Manufacturing Company (IMC), acquired in 1964.<ref name=history/>

At the time, IMC was in the process of industrialising a unique South African invention, the [[Tellurometer]], the first successful microwave electronic distance measurement equipment.<ref>{{Cite web|url=https://celebrating200years.noaa.gov/distance_tools/tellurometermra1.html|title=Going the Distance: A Photo Collection Illustrating the History of Distance Measurement Tools at the National Geodetic Survey|first=National Oceanic and Atmospheric Administration|last=US Department of Commerce|website=celebrating200years.noaa.gov|access-date=16 April 2020|archive-date=31 December 2019|archive-url=https://web.archive.org/web/20191231074713/https://celebrating200years.noaa.gov/distance_tools/tellurometermra1.html|url-status=live}}</ref> The instrument was invented by [[Trevor Wadley|Dr. Trevor Lloyd Wadley]] of the Telecommunications Research Laboratory of the South African Council for Scientific and Industrial Research (CSIR), also responsible for the [[Wadley loop]] receiver, which allowed precision tuning over wide bands, a task that had previously required switching out multiple crystals.

South African insurance and investment company [[Sanlam]] bought 26% of Plessey South Africa in 1974, with first right of refusal to purchase more of the company.<ref>{{Cite web|url=https://www.is.co.za/home/|archive-url=https://web.archive.org/web/20090228063822/http://www.plessey.co.za/history.php|url-status=dead|title=Internet Solutions &#124; Making the world work better|archive-date=28 February 2009|website=Internet Solutions}}</ref> These shares were later transferred to Sankorp, Sanlam's industrial holdings company. In 1989, when GEC-Siemens took control of the Plessey Company, Sankorp indicated its intention to purchase the remaining 74% of shares in the South African subsidiary.

=== Australia ===
Plessey had a manufacturing plant at Meadowbank in Sydney, Australia<ref>The Encyclopedia of Australian Science and Innovation https://www.eoas.info/biogs/A001342b.htm</ref> that made defense equipment and TVs. In the 1970s and 80s it produced Ericsson Crossbar Telephone Exchanges under licence for Telecom Australia and the PNG Post and Telegraphs department.{{Citation needed|date=July 2022}}

===GEC takeover bid===
In December 1985, [[General Electric Company|GEC]] launched a takeover bid for the Plessey Company, valuing the group at £1.2&nbsp;billion. Both Plessey and the [[Ministry of Defence (United Kingdom)|Ministry of Defence]] were against the merger, since GEC and Plessey were the two largest suppliers to the MoD and in many tenders the only competitors. In January 1986, the bid was referred to the [[Competition Commission|Monopolies & Mergers Commission]] (MMC), whose report published in August advised against the merger. The government concurred and blocked GEC's bid.<ref name=SP-H-01/><ref name=SP-H-02/>

In 1988, Plessey and GEC merged their telecom units to form [[GEC Plessey Telecommunications]] (GPT), at the time the UK's leading telecommunications manufacturer.

===GEC Siemens takeover===
In 1988, GEC and [[Siemens]] set up a joint [[holding company]], GEC Siemens, to launch a hostile takeover of Plessey. Their initial offer was made on 23 December 1988, valuing Plessey at £1.7&nbsp;billion. Again, Plessey rejected the offer and again it was referred to the MMC. The original proposal envisaged joint ownership of all of Plessey's defence businesses, with GPT and Plessey's North American businesses split in the ratios 60:40 and 51:49 respectively. The level of GEC's involvement in the Plessey defence businesses was not likely to meet with regulatory approval and in February 1989, GEC Siemens announced a new organisation. In an effort to head off the bid, Plessey announced in May 1989 the closure of its [[compound semiconductor]] business in [[Towcester]], Plessey 3-5. The takeover was completed in September 1989.<ref name=SP-H-01/><ref name=SP-H-02/><ref>{{Cite web|url=http://www.ipdgroup.com.au/Page/About+Us/GEC+History.aspx|archive-url=https://web.archive.org/web/20100329015638/http://www.ipdgroup.com.au/Page/About%20Us/GEC%20History.aspx|url-status=dead|title=404 Page Not Found|archive-date=29 March 2010|website=www.ipdgroup.com.au}}</ref>

==Break-up of the business==
In April 1990, GEC and Siemens agreed a new structure of ownership of the Plessey businesses:<ref name=SP-H-01/><ref name=SP-H-02/><ref>{{cite news | title = The Plessey Carve-up | work = [[Financial Times]] | publisher = The Financial Times Limited | page = 26| date = 4 April 1990 }}</ref>

===GEC acquisitions===
*In the UK
**Plessey Aerospace
**Plessey Avionics
**Plessey Crypto
**Plessey Materials
**Plessey Naval Systems
**Plessey Semiconductors
**[[Plessey Research Caswell]]
**Plessey Microsystems
**Plessey Controls
*In North America
**Plessey Aero Precision Corp
**Plessey Dynamics Corp
**Plessey Electronic Systems Corp (including ES Marine Systems)
**Sippican
**Plessey Materials
**Leigh Instruments

===Siemens acquisitions===
*Siemens Plessey Radar
*Siemens Plessey Defence Systems
*Siemens Plessey Controls
*Siemens Plessey Australia
*Siemens Plessey Assessment Services
*[[Roke Manor Research]]

===Jointly owned===
*[[GEC Plessey Telecommunications]]: 60% GEC and 40% Siemens

===Disposals===
*Birkby Plastics (1989-1990)<ref>{{Cite web|url=https://www.birkbys.co.uk/sire/site_history_main.asp|title=Birkbys|access-date=2023-03-26|archive-date=2008-10-25|archive-url=https://web.archive.org/web/20081025022734/http://www.birkbys.co.uk/site/site_history_main.asp|url-status=dead}}</ref>
*Hoskyns Group
*Plessey Valdarno S.p.A. (Italy), sold to [[Magnetek]] in 1991<ref>{{cite news |last1=Corsi |first1=Marco |title=Addio all'ingegner Antonio Canova. Manager della Plessey e poi della Magnetek, ha contribuito allo sviluppo economico del Valdarno |url=https://www.valdarno24.it/2021/12/19/addio-allingegner-antonio-canova-manager-della-plessey-e-poi-della-magnetek-ha-contribuito-allo-sviluppo-economico-del-valdarno/ |access-date=26 March 2023 |work=Valdarno 24 |date=19 December 2021 |language=it}}</ref>
*51% share in Plessey Telenet acquired by minority partner in 1992
*74% share in Plessey South Africa acquired by minority partner Sankorp

==Subsequent history==
===UK===
In 1997, [[British Aerospace]] and [[DaimlerChrysler Aerospace]] acquired the UK operations and the German part of [[Siemens Plessey]] Systems, respectively.<ref>{{Cite web|url=https://news.bbc.co.uk/2/hi/business/18740.stm|title=BBC News &#124; Business &#124; British Aerospace buys Siemens|website=[[BBC News]]|access-date=16 April 2020|archive-date=10 March 2016|archive-url=https://web.archive.org/web/20160310120658/http://news.bbc.co.uk/2/hi/business/18740.stm|url-status=live}}</ref>

By 1997, the GPT name disappeared in the UK and the company was known as Siemens GEC Communication Systems (SGCS), which later became [[Siemens Communications]]. In August 1998, GEC acquired Siemens' 40% stake in GPT (by now only existing as a legal entity) and merged GPT with the telecoms units of its other subsidiaries, namely Marconi SpA, GEC Hong Kong and ATC South Africa, to form [[Marconi Communications]]. In December 1999, GEC's defence arm [[Marconi Electronic Systems]] was amalgamated with British Aerospace to form BAE Systems.

The remainder of GEC was renamed to Marconi plc, and Marconi Communications became its principal subsidiary.<ref>[http://networks.silicon.com/telecoms/0,39024659,11001302,00.htm GEC buys Siemens out of GPT] {{webarchive|url=https://web.archive.org/web/20080820040308/http://networks.silicon.com/telecoms/0%2C39024659%2C11001302%2C00.htm |date=20 August 2008 }}</ref> This company was affected by the [[dot-com bubble]] and was restructured into Marconi Corporation in 2003, then collapsed in 2005. Most of it (including Marconi Communications) was bought by [[Ericsson]] and the remainder became [[Telent]].

The part of GPT which evolved into Siemens Communications would eventually become [[Unify (company)|Siemens Enterprise Communications]] in 2008.
[[File:Plessey Semiconductors Swindon 1982.jpg|thumb|right|500px|Plessey Semiconductors factory at Cheney Manor, Swindon in 1982. The factory housed both bipolar and MOS lines. A small part of the canteen facilities (which had five grades of service) for all Plessey employees is visible on the right of the image, since demolished around 2010]]GEC Plessey Semiconductors (GPS) was purchased by [[Mitel]] Semiconductors of Canada in 1998.<ref>{{cite web|url=http://findarticles.com/p/articles/mi_m0EKF/is_/ai_20323831 |title=FindArticles.com – CBSi |url-status=dead |archive-url=https://web.archive.org/web/20081231070308/http://findarticles.com/p/articles/mi_m0EKF/is_/ai_20323831 |archive-date=31 December 2008 }}</ref> After a number of downsizes, including the purchase of the power semiconductor and [[silicon on sapphire]] operation at [[Lincoln, Lincolnshire]] by [[Dynex Semiconductor]] in 2000, the company renamed itself [[Zarlink]] Semiconductor in 2001.<ref>{{Cite web|url=http://articles.janes.com/notice.html|title=Defense & Security Intelligence & Analysis: IHS Jane's &#124; IHS|website=articles.janes.com|access-date=16 April 2020|archive-date=18 March 2013|archive-url=https://web.archive.org/web/20130318075501/http://articles.janes.com/notice.html|url-status=live}}</ref> The GPS fabrication plant in [[Plymouth]] was acquired by [[X-Fab|Xfab]].

===Plessey Semiconductors Ltd===
After the sale of the [[Roborough, South Hams|Roborough]] site in [[Plymouth]] to [[X-Fab|Xfab]], the original Plessey Semiconductors site at Cheney Manor, Swindon continued to operate under the Zarlink Semiconductor name until it was sold to MHS Industries in early 2008. In February 2009, the UK business was forced into receivership following the collapse of the parent MHS Electronics business in France. After a subsequent management buyout the company traded as Plus-Semi Ltd.<ref>{{Cite web|url=http://www.xfab.com/de/main/about-x-fab/news/news-archiv/select/news.html?tx_ttnews%5Byear%5D=2009&tx_ttnews%5Bmonth%5D=12&cHash=80e445e3fbe04501eceee1ce527dd5fc|archive-url=https://web.archive.org/web/20120322071419/http://www.xfab.com/de/main/about-x-fab/news/news-archiv/select/news.html?tx_ttnews%5Byear%5D=2009&tx_ttnews%5Bmonth%5D=12&cHash=80e445e3fbe04501eceee1ce527dd5fc|url-status=dead|title=''X-FAB und Plus Semi vereinbaren Verkauf von X-FAB UK'' Press release from X-FAB 1 December 2009, accessed 9 April 2012|archive-date=22 March 2012}}</ref><ref>{{Cite web|url=http://www.linkedin.com/company/plus-semi|title=Linkedin page of Plus Semi|access-date=2012-04-09|archive-date=28 October 2012|archive-url=https://web.archive.org/web/20121028232429/http://www.linkedin.com/company/plus-semi|url-status=live}}</ref>[[File:Former Plessey Microelectronics Factory Swindon.jpg|thumb|right|Plessey Semiconductors factory at Cheney Manor, Swindon, on 17 July 2012, undergoing demolition]]
The Roborough site ( 8" and 6" lines) was re-acquired from [[X-Fab|Xfab]] on 1 January 2010 and the company renamed as Plessey Semiconductors Ltd. The new company transferred its [[Bipolar junction transistor|bipolar]] processes on silicon and [[silicon on insulator|SOI]] into the 8" Plymouth facility during 2010, exploiting the combined technology base in the development of new processes and products in a number of markets. The Swindon site on the Cheney Manor Industrial estate in the west of the town was demolished in July 2012. In 2011/2, Plessey acquired the rights to disruptive GaN-on-silicon technology by acquisition of CamGaN, a startup company, from Cambridge Enterprises.<ref>{{Cite web|url=https://www.enterprise.cam.ac.uk/news/cambridge-spin-out-camgan-acquired-by-plessey/|title=Cambridge spin-out CamGaN acquired by Plessey|website=Cambridge Enterprise|language=en-GB|access-date=3 September 2019|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104915/https://www.enterprise.cam.ac.uk/news/cambridge-spin-out-camgan-acquired-by-plessey/|url-status=live}}</ref>

Using the GaN-on-silicon technology and semiconductor expertise, Plessey Semiconductors Ltd manufactured solid state lighting, horticultural lighting and medical sensing products. Their GaN-on-silicon i2LED high power LEDs and Stellar Orion Beam Forming modules, launched in autumn 2016, which enabled new form factors of lighting products and remove critical design constraints for lighting product designers. In horticulture, the Plessey Attis Growlight was at the forefront of an engineering approach to LED based plant grow lights which was then developed into a new brand, Hyperion Grow Lights.<ref>{{Cite web|url=http://www.hyperiongrowlights.com/|title=Home|website=Hyperion Grow Lights|access-date=3 September 2019|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104906/http://www.hyperiongrowlights.com/|url-status=live}}</ref> The company's medical products were based on the EPIC sensor, which were used in the advanced portable ECG monitoring device, Impulse, and was also the basis of an R&D program, named Warden, to develop driver alertness monitoring devices in automotive and aeronautical applications.<ref>{{Cite web|url=https://plesseysemiconductors.com/|title=Plessey &#124; microLEDs|date=3 April 2020|website=Plessey|access-date=16 April 2020|archive-date=6 April 2020|archive-url=https://web.archive.org/web/20200406045014/https://plesseysemiconductors.com/|url-status=live}}</ref>

In 2017, Plessey pivoted the focus of the business to the R&D and manufacturing of microLEDs (micro light-emitting diodes) as a market disrupting display technology for a wide range of applications, including: Augmented Reality, Mixed Reality, smartphones, televisions, smartwatches, head-up displays, head-mounted displays and more.<ref>{{Cite web|url=https://www.linkedin.com/company/plessey-semiconductors/|title=LinkedIn: Plessey Semiconductors Ltd|date=October 2013 |access-date=3 September 2019|archive-date=19 February 2014|archive-url=https://web.archive.org/web/20140219134616/http://www.linkedin.com/company/plessey-semiconductors|url-status=live}}</ref>
[[File:Plessey HQ Aug 2017.jpg|thumb|Plessey Semiconductors headquarters in [[Roborough, South Hams|Roborough]], [[Plymouth]] in August 2017]]
Plessey continues to operate in the Roborough site<ref>{{Cite web|url=https://beta.companieshouse.gov.uk/company/04129612|title=PLESSEY SEMICONDUCTORS LTD - Overview|postscript=→(free company information from Companies House)|website=beta.companieshouse.gov.uk|language=en|access-date=2019-09-03|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104905/https://beta.companieshouse.gov.uk/company/04129612|url-status=live}}</ref> with leading-edge 150mm and 200mm wafer processing facilities to undertake design, test and assembly of products, and a comprehensive suite of photonic characterisation and applications laboratories.

Their original microLED product was an illuminator for display light engines (DMD and LCOS), which offered a 40% reduction in light engine size whilst delivering higher energy efficiency. They have now upgraded to full-field emissive microLED displays that combine very high-density RGB pixel arrays with high-performance CMOS backplanes to produce very high-brightness, low-power and high-frame-rate image sources. These are innovative products that are widely recognised within the industry with many accolades from prestigious electronics, engineering and display industry award programs, including: Elektra Awards 2017,<ref>{{Cite web|url=https://www.elektraawards.co.uk/elektraawards2019/en/page/2017-winners|title=Elektra Awards 2019 - 2017 Winners|last=Metropolis|website=elektraawards.co.uk|language=en|access-date=3 September 2019|archive-date=4 September 2019|archive-url=https://web.archive.org/web/20190904090539/https://www.elektraawards.co.uk/elektraawards2019/en/page/2017-winners|url-status=live}}</ref> British Engineering Excellence Awards 2017,<ref>{{Cite web|url=http://www.eurekamagazine.co.uk/design-engineering-features/technology/meet-the-winners-of-the-2017-british-engineering-excellence-awards/163440/|title=Meet the winners of the 2017 British Engineering Excellence Awards|website=www.eurekamagazine.co.uk|date=11 June 2017 |access-date=3 September 2019|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104906/http://www.eurekamagazine.co.uk/design-engineering-features/technology/meet-the-winners-of-the-2017-british-engineering-excellence-awards/163440/|url-status=live}}</ref> National Technology Awards 2018,<ref>{{Cite web|url=http://www.nationaltechnologyawards.co.uk/|title=National Technology Awards|website=www.nationaltechnologyawards.co.uk|access-date=3 September 2019|archive-date=23 August 2019|archive-url=https://web.archive.org/web/20190823073217/http://nationaltechnologyawards.co.uk/|url-status=live}}</ref> CES Innovation Awards 2019<ref>{{Cite web|url=https://www.ledinside.com/press/2018/11/plessey_micro_led_displays_receives_ces_2019_innovation_award|title=Plessey's Micro LED Displays Receives a CES 2019 Innovation Award|website=www.ledinside.com|language=en|access-date=3 September 2019|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104916/https://www.ledinside.com/press/2018/11/plessey_micro_led_displays_receives_ces_2019_innovation_award|url-status=live}}</ref> and Electronics Industry Awards 2019.<ref>{{Cite web|url=https://www.electronicsindustryawards.co.uk/winners-2019/|title=Winners 2019 {{!}} Electronics Industry Awards 2019|date=23 May 2019 |language=en-GB|access-date=3 September 2019|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104910/https://www.electronicsindustryawards.co.uk/winners-2019/|url-status=live}}</ref>

In March 2019, Plessey used their GaN-on-silicon technology, which natively emits blue, to innovatively engineer the early layers within the process to emit native green,<ref>{{Cite web|url=https://www.electronicsweekly.com/blogs/led-luminaries/plessey-developed-native-green-led-microdisplay-2019-04/|title=Why has Plessey developed a native green led microdisplay?|last=Bush|first=Steve|date=5 April 2019|website=Electronics Weekly|language=en-GB|access-date=3 September 2019|archive-date=16 August 2019|archive-url=https://web.archive.org/web/20190816062239/https://www.electronicsweekly.com/blogs/led-luminaries/plessey-developed-native-green-led-microdisplay-2019-04/|url-status=live}}</ref> opening more opportunities for markets such as military. Plessey also achieved the world's first GaN-on-silicon monolithic, wafer to wafer bonding, in May which was a massive breakthrough for not only the company but the industry.<ref>{{Cite web|url=https://optics.org/news/10/5/24|title=Plessey and Jasper develop GaN-on-Si HD microLED display|website=optics.org|access-date=3 September 2019|archive-date=3 September 2019|archive-url=https://web.archive.org/web/20190903104916/https://optics.org/news/10/5/24|url-status=live}}</ref>

In 2025, Plessey Semiconductors was acquired by Haylo Labs, using funding from Chinese AI [[smartglasses]] manufacturer Goertek Inc. The acquisition was given national security clearance after a review under the [[National Security and Investment Act 2021]].<ref name=thereg-20250820>{{cite news |url=https://www.theregister.com/2025/08/20/china_funding_backs_plessey/ |title=Chinese funding backs sale of British microLED specialist |last=Robinson |first=Dan |website=The Register |date=20 August 2025 |access-date=21 August 2025}}</ref>

===South Africa===
In South Africa, following the successful GEC/Siemens takeover, after protracted negotiations in 1991, Plessey South Africa became a wholly owned subsidiary of Sankorp under the new name of Plessey Tellumat South Africa Limited (PTSA). The addition of the name Tellumat had a double symbolism, firstly for the company's commitment to exports, as it is the name of its UK-based export subsidiary. Secondly, the name derives from the Tellurometer, South Africa's world first electronic surveying development—and by implication, a commitment to ongoing electronic research and development.

PTSA continued to grow with a strong focus on telecommunications and defence products, particularly with a major expansion into large projects, rolling out the microwave backbone of MTN, one of South Africa's first GSM cellular networks and the installation of a fibre optic network and radio broadcasting system in Malaysia. A software division was formed through the acquisition of BSW data, largely staffed by engineers from the recently terminated South African space programme in which PTSA had also participated, both in the electronics of the launch vehicle and the satellite itself.

1995 was a landmark year in the history of the business in South Africa. The merger of PTSA and Tek Electronics, the consumer electronics audio and video products, manufacturer and distributor, (also wholly owned by Sankorp) took the business full circle back to its consumer electronics roots.<ref name=history/> This resulted in the renaming of PTSA back to the original name of ''Plessey South Africa'' Limited. The full acquisition of AWA-Plessey Communications, which Plessey jointly owned in Australia with Amalgamated Wireless (Australasia) Ltd (AWA) and had a similar product portfolio, resulted in penetration into the Pacific Rim market. The culmination of this growth was the company's listing on the Johannesburg Stock Exchange (JSE) as the ''Plessey Corporation'' in the same year.  Trading started off at R4.80 a share.<ref name=history/> On the evening of 6 February 1996, a devastating fire swept through two bays of the White Road factory in Retreat, [[Cape Town]] causing huge damage to stock, instruments, plant and work in progress. No one was injured, but work was disrupted for several weeks. Large sections of the factory had to be rebuilt.<ref name=history/>

At the end of 1996, Plessey Corporation sold off the Sales and marketing business of Telefunken, Pioneer and Satellite TV.<ref name=history/>

In August 1998, Plessey Corporation was bought by [[Dimension Data Holdings]] and Worldwide African Investment Holdings for R1.6 billion. The new owners retained BSW Data, Plessey Solutions and Communications Systems. The remaining divisions, notably with a product development and manufacturing focus, were bought back by a combined management buyout supported by Rand Merchant Bank. The corporate name was changed to Tellumat Pty Ltd.<ref>{{Cite web|url=http://www.tellumat.com/group/co-intro.htm|archive-url=https://web.archive.org/web/20081227065044/http://www.tellumat.com/group/co-intro.htm|url-status=dead|title=Tellumat: Introduction|archive-date=27 December 2008}}</ref> Tellumat continues to develop and manufacture Plessey-branded products as before and operates in the [[Defense (military)|defence]], [[telecommunications]] and contract manufacturing markets.

==Plessey barcodes==<!-- This section is linked from [[Barcode]] -->
{{main article|Plessey Code}}
[[Image:Plessey barcode.png|thumb|right|"''123456E''" encoded in a Plessey barcode]]

The name is also used to refer to a [[barcode]] symbology developed by Plessey, which is still used in some [[library|libraries]] and for shelf tags in retail stores, in part as a solution to their internal requirement for stock control. The system was first used in the early 1970s by [[Sainsbury's|J.Sainsbury]] to identify all of its products on supermarket shelves for its product restocking system. The chief advantages are the relative ease of printing using the dot-matrix printers, which were popular at the time of the code's introduction, and its somewhat higher density than the more common 2 of 5 and 3 of 9 codes.

Plessey barcodes use two bar widths. Whitespace between bars is not significant. The start element is a wide bar, and the stop element is two narrow bars. In between, the bars are in groups of four. High order bars appear leftmost. Narrow bars are 0 and wide bars are 1.

This symbology is not self checking, though a modulo 10 or modulo 11 checksum (or some combination of both checksums, depending on application) is usually appended.

==References==
{{reflist|refs=
<ref name=SP-H-01>{{cite book|title= The Integration of Acquired Companies into the Defence Industry: Experiences|date= August 1996|isbn= 9780788148590|url= https://books.google.com/books?id=3wA28RpeycwC&pg=PA23|access-date= 16 July 2012|last1= Backlund|first1= Karin|last2= Sandstrom|first2= Madelene|publisher= DIANE|archive-date= 15 January 2022|archive-url= https://web.archive.org/web/20220115213321/https://books.google.com/books?id=3wA28RpeycwC&pg=PA23|url-status= live}} by Karin Backlund, Madelene Sandstro</ref>
<ref name=SP-H-02>{{cite web|title='The DECCA Legacy' A view from inside the RADAR company -DECCA – BAE SYSTEMS (1949–2009)|url=http://www.woottonbridgeiow.org.uk/decca-legacy/chapter2.php|access-date=16 July 2012|archive-date=6 April 2019|archive-url=https://web.archive.org/web/20190406124258/http://www.woottonbridgeiow.org.uk/decca-legacy/chapter2.php|url-status=live}}</ref>
}}

==External links==
*[https://web.archive.org/web/20040628163409/http://web.ukonline.co.uk/freshwater/histples.htm History of Plessey]
*[https://sites.google.com/site/plesseyaddlestonereunion/plessey-company-history Plessey history]

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