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Protecting Northern Ireland’s Infrastructure

With any conflict comes a risk to national infrastructure by terrorist organisations as a means to exert power and create panic and unrest among the population in the name of their cause. Long before the official start of Operation Banner in 1969, local Government and security forces (SF) were concerned about the security of key installations across Northern Ireland (NI) such as power stations, telephone exchanges, radio transmitters and reservoirs. In 1979 it was known from intelligence sources that it was a Provisional Irish Republican Army (PIRA) policy to attack targets in the field of transport and communications (National Archive CJ4/2852). These sites were known as Key Points (KPs) and a civil Key Points Committee (KPC) was tasked with evaluating the risk to and advising on the protective measures for hundreds of these sites across NI. While the security forces were responsible for the protection of their own sites, there were circumstances where they also protected a number of these KPs.

To quote National Archive record CJ 4/4424 Key Points Committee Organisations and Bodies – “A key point (KP) is any installation, the products or services of which are of such importance that total loss or severe damage would seriously impair one or more of their following:

  1. The functioning of the government or security forces;
  2. The economy;
  3. Public utilities serving large centres of population.

A Target Installation (TI) is an installation which may become a target either because it provides an important public service ore employment for a significant number of people, or because its contents are potentially attractive to terrorists or dangerous in themselves.”

A further definition is that of Vulnerable Point (VP), being any particular element within a KP that, if put out of action, would lead to serious disruption. Those KPs that helps significate economic value were detailed as Economic Key Points (EKPs).

Following review, the nature of protection that could be awarded to each site ranged from security patrol visits through to full-time static guards. These physical security measures were categorised as either measures to protect the shell of a building, measures to protect the external perimeter and aids to detection and surveillance. The review of each site had to take into consideration a number of factors:

Following review, the nature of protection that could be awarded to each site ranged from security patrol visits through to full-time static guards. These physical security measures were categorised as either measures to protect the shell of a building, measures to protect the external perimeter and aids to detection and surveillance. The review of each site had to take into consideration a number of factors:

  • The (current) terrorist threat
  • The local (political and social) situation
  • Existing protective security measures
  • Other (security force) operational commitments

“Major disruption would normally only result from a well planned terrorist attack carried out by persons with some experise or insider knowledge.”

– Quote from the Key Points Review Body (KPRB) first report

However, any physical security measure can be overcome with enough determination on behalf of the attacker, but usually at the sacrifice of time, noise or technical complexity. The main focus of protecting KPs was to deter and delay all but the most determined attempts, and in the case of unmanned sites, to alert the SF to any breach. By the end of 1981 there were 80 key points across NI that included water, electricity, communications and gas installations along with Aldergrove airport and industrial complexes. Of these 80, only nine had been allocated permanent guards; six at electricity installations, two at BT owned telecoms centres and one at the BBC transmitter at Divis.

Key Points & Target Installations

Reservoir, Silent Valley

As far back as May 1957 it had been decided to provide a permanent police protection post at the Silent Valley Reservoir (PRONI, HA/32/1/1376). When it was established it was manned by a Sergeant and seven Special Constables, however in February 1958, such was the threat, that this had been increased to one Sergeant and fifteen Special Constables. The rather isolated post was equipped with a Marconi receiver/transmitter set, living quarters for the policemen, a generator for backup power, an Army 1-ton lorry and at least two Vespa Model 42L2 dual seat scooters. They also had responsibility for guarding the nearby Ben Crom reservoir that was also under construction 3 miles away.

From descriptions, this is the most likely location of the police protection post in 1957 protecting Silent Valley and Ben Crom reservoirs in the Mourne Mountains, County Down. Photograph 2017, the author.

BBC Transmitter, Divis Mountain

The BBC site at Divis. Photograph 2008, the author.

Key Point Green 2 (as it was once designated) the BBC transmitter on Divis Mountain occupied a site of 1.5 acres, 390m above sea level and was accessed by a 1.5 mile track from the public road. The Army provided a permanent guard consisting up to 8 soldiers at this site from 1973 until private security staff took over in 1982. The station was the main BBC radio and TV transmitter for NI and provided a vital link between RTE and mainland GB. It was a good example of KP protective measures having an impressive set of defences (as of 1983) – two outer fences, each 10ft high, barbed wire occupying the space between each which was also flood lit at night, CCTV covering the entrance, an air-lock system for entry into the compound, communications between the gate and the operations room, direct radio link with the RUC, all unnecessary windows bricked up and doors covered with steel sheet.

While no credible threat had been received to the transmitter, the consequences of any disruption to operation could have been a loss of transmission for 2-3 days, restricted service for ups to 18 months. There would have been an adverse effect on the morale of the NI population, communications with GB would have been affected and local broadcasting companies would have suffered financial loss as a result of the downtime. With such a large and significant site sitting in a very exposed position, surrounded by bog, a long distance from the public road and one that was prone to low cloud and fog, it was important the site be protected.

Electricity Sub-Station, Kells

Kells sub-station. The image is from 2018, but some of the 1970s era protective measures can still be seen.

The electricity sub-station at Kells, 6.5 miles outside Ballymena was identified as a KP with a number of VPs and as such underwent a secret security review in 1978. It distributed power to the north-east of NI and at the worst may take up to 2 years to repair in the instance of the relay room being destroyed. At the height of the Troubles, army static guards were sited here. Based on the recommendations of the KP review board (KPRB) a sterile area outside the perimeter was established, covered by CCTV and a perimeter intrusion detection system (PIDS) was provided – all of which can still be seen today. If you look at the base of the nearest CCTV mast you can see a short horizontal bar of a PIDS sensor.

Telephone Exchange, Bushmills

Like most telephone exchanges they were vital communication hubs that were vulnerable to terrorist attack.

Bushmills telephone exchange was classified as a Green Target Installation (TI). It served a relatively modest 600 connections but also served the nearby air traffic navigation Consul station, meaning disruption may have a greater impact. The exchange was adjacent to Bushmills police station, and behind the perimeter wire, offering greater protection than most had.

Protective Measures

While permenant military presence at a Key Point was infrequent, the presence of a Target Installation in a local area called for greater scrutiny from the Security Forces. With frequent and irregular patrols in the area, they sought to reassure civilian staff and security personnel who were stationed at the site. They would also be able to check outer perimeters and conduct random checks of internal Vital Points, especially in the case of ungaurded KPs. The SF could also conduct Vehicle Check Points (VCPs) in the area and on approach to any KP to deter any would-be attackers.

External Protection

The shells of conventional buildings offer little protection against the determined attacker and are susceptible to breach after a few minutes. Methods of reinforcing windows and doors provide little additional delay, but if blocking them up is a viable option, then this will help slow an attack. For small unmanned buildings this is often an acceptable course of action to take. One such category of building for which this protection was appropriate was the unmanned radio transmitter site, often located on remote hilltops they would be left unattended, and depdndant on their function any hostile actions could have varying levels of disruption.

The military transmitter site on Craigantlet Hills overlooking Belfast. This unmanned site has had all windows blocked up and sits within a double chain link fence compound topped with barbed wire.

Where it was assessed that a manned guard was essential, in addition to perimeter protection, armoured guard posts were installed. Initially when the Army was called in to protect sites they would have been housed in defences more akin to the battlefield; sandbagged sangars. However, while the Army had greater means of engagement against an armed attacker, the purpose of the civilian static guards became focussed on controlling access, patrolling as a means of being a deterrant and to alert an appropriate reaction force should the need arise. The civilian static guards were accomodated in more appropriate accommodation such as the example of a guard post at Kilroot power station:

Security post at Kilroot power station, outside Carrickfergus. The same design of armoured post can be seen at police stations throughout NI.

From what I can establish, the most guarded civilian Key Point was the microwave relay station at Ballygomartin, on the Belfast side of Divis Mountain. It was designated Key Point Green 1 and was a permenant, guarded site. This relay station provided one of the main wireless links for telephone and TV to the GB mainland and as such was a strategic target to protect. The station had a formidible set of defences based mostl likely on reccommendations from the Key Point Committee and security force advice:

  • External 20ft high fence surrounding the perimeter. Not chain link but a newer weldmesh steel. This was topped with barbed (also known as dannert) wire.
  • Behind the external fence was a further row of barbed wire at ground level.
  • This was sandwiched between the outer fence and an electrified inner fence.
  • A row of security lights illuminated the exterior of the site, dazzling any nightime attackers and illuminating the ground surrounding the site.
  • All buildings identified as vulnerable points had their windows covered with steel shutters. Doors were also steel.
  • The site had an armed military guard. There was a brick guardpost observing the exposed rear of the site. There was a standing requirement for a 4 strong static guard from the Springfiled Road Battalion
Double fence comprising weldmesh steel exterior, barbed wire middle and an electric fence interior. All illuminated by floodlights. It would take a very determined attacker to breech this perimeter.
More akin to a military installation an armed guardpost was constructed to protect the rear of the site.

Intruder Detection

The conventional method of protecting a perimeter is by foot patrol, but this is easy to overcome. The 1970s saw the development of electronic surveillance systems which were prefereable for twenty four hour cover.

“Reliable equipment is available to provide electronic surveillance of the interior of buildings, but detection at this stage of intrusion is usually too late to forestall the attack.”

– Quote from the Key Points Review Body (KPRB) first report

An early development detailed in official documents was a system under review by the Home Office Scientific Advisory Branch (HOSAB) was being developed by Plessey. This was most likely the Plessey 3PS Perimeter Protection System. This system operates using a buried coaxial cable running a transmit and a receive circuit to detect disturbances in the radio field generated. It is unclear if this system became operational in NI following the HOSAB trials, but what does still remain is evidence of an alternative technology.

Known commonly as microwave fences, the above ground systems were most likely manufactured by Shorrock Security Systems. A chain of microwave transmitters and receivers were placed at intervals and operated either in a break beam mode or they could detect variations in beam strength upon the presence of an intruder.

Perimeter Surveillance System most likely manufactured by Shorrock and installed on high value target installations. This example was in place at the ex-GCHQ Y-station at Gilnahirk.

Another possible detector in use was the ground vibration sensor. Installed around the Maze Prison were a series of steel cylinders sunk into the ground. Perhaps as a method for detecting vibrations in the event of a vehicle approaching across the perimeter. At this stage there is no evidence to support this.

Possible ground vibration sensor at the Maze Prison.


The designation and protection of Key Points was a priority for security forces in Northern Ireland during Operation Banner as the impact of any disruption to national infrastructure could have severe political, social or economic implications. The methods used to protect such sites ranged from secure fences to blocking windows and doors and in some cases placing a static civilian or military guard on the site. It is safe to say that even if you do not see protection, that it probably exists and all the technology mentioned in this article was introduced in the 1970s and 1980s – modern systems will be much more capable. If you look closely at some of the likely sites identified as Key Points you may find some legacy protective measures.

Key Point Defence Notes

Browsing a Commanders Battle Book from 1988, I came across tactical check notes on the defence of Key Points. In times of heightened threat the army was often deployed to KPs for their protection. This aide memoir details the actions that would have been taken by troops when securing and protecting the KP.

Tactical check notes on Key Points from the Commanders Battle Book, 1988

To decode some of the military language, here is the recommended sequence of events when taking over or securing a KP:

  • Planning and preparation involves consulting the KP dossier; what is the role of the KP? Details of the KP and any Vulnerable Points (VP), photographs and diagrams of the site including maps and boundary and any suggested defensive plan recorded on file.
  • What existing security measures are in place; fences, access points, VPs, Observation Points (OPs) and sangars, trenches or any patrols.
  • Devise a patrol programme and secure any Ground Defence Area (GDA).
  • A reminder that there may also be external tasks to the main KP.
  • If there is any engineer support there will be an allocation of defence stores, they may need to construct, extend or repair the perimeter fence or provide other physical protection measures.
  • Check if any other assistance is available; police, helicopters or dogs.

Appendix A: Table of main Key Points

Green 1Radio Station, BallygomartinP(G)Vital microwave terminal for telephony and TV.
Green 2Telephone House, Cromac Street, BelfastP(G)Telephony, TV, HF and Telex links. Handles emergency calls for Greater Belfast.
Green 3Telephone Exchange, Pasadena Gardens, BelfastP(NG)Includes connections to HQ RUC, Knock, Gilnahirk Radio Station and Dundondald House.
Green 4Telephone Exchange, Paulette Avenue, BelfastP(NG)Serves RUC HQ Belfast, Yellow 1, Yellow 3 and RUC Training Centre at Old Ropeworks.
Green 6Telephone Exchange, Railway Street, LisburnP(NG)Connections including Thiepval Barracks, RUC HQ. PCM terminal.
Green 7Cable Station, Millisle Road, DonaghadeeP(NG)Open terminal and test apparatus for undersea cables. Equipment very difficult to replace.
Green 8Telephone Exchange, Queens Quay, LondonderryP(NG)Connections including Ebrington Barracks, HF, VHF and PCM terminal. Handles emergency calls for North Londonderry.
Green 9Telephone Exchange, Kelvin Road, OmaghP(NG)Emergency calls in County Tyrone. HF, VHF and PCM terminal.
Green 10 – 15Missing from archives
Green 16RUC Workshops, Lislea Drive, BelfastP(G)
Green 17Telephone Exchange, Carrickblacker Road, PortadownP(NG)Emergency calls for North and Mid-Armagh. Main PO emergency centre. HF, VHF and PCM terminal.
Green 18Telephone Exchange, Downshire Road, NewryP(NG)Emergency calls for South Armagh and South Down. HF and VHF terminal.
Green 19Telephone Managers Office, Churchill House, BelfastP(NG)Area HQ for NI
Green 20City Telephone Exchange, Durham Street, BelfastP(G)Telex and Teleprinter exchange for NI. Handles 999 connections for City Centre and West Belfast.Ê
Green 21Ballymena Telephone Exchange, Troston AvenueP(NG)Emergency calls of Mid-Anrim. Main PO emergency centre. HF and VHF terminal. NI-GB standby Post Office terminal.

P(NG) – Permanent Key Point, Not Guarded
P(G) – Permanent Key Point, Guarded

Appendix B: Non-Telephone Exchange, Unguarded Key Points

119Radio Station, CromkillVHF terminal providing standby terminal link to GB.
134ITA Transmitter, Black MountainITV Transmitter
136Deadman’s Hill Relay Station, Friary Road, NewtownardsMicro-wave relay station with Standing Stones (144) relay station handles Belfast-Dublin and Dublin-GB traffic.
137Clanrolla Decca Navigation StationPart of the North British chain providing navigation data for shipping and aircraft.
141Repeater Station, Belfast Road, Donaghmore, NewryCo-axial repeater in Belfast-Dublin cable.
143Radio Station, Shanes Hill Road, BallymenaVital VHF repeater in Cromkill-GB telephony link.
144Standing Stones Radio Station, Bundore, HannahstownMicrowave terminal Belfast-Dublin telephony and TV link.
145Repeater Station, Knockmore, Hull’s LaneCo-axial repeater in Belfast-Dublin cable.
148Repeater Station, Ardglass, BallyhornanTerminal for submarine cable to GB.
171BBC Site, Glenderowen New Buildings, Londonderry
172BBC Site, Maddybennymore
173BBC Site, Coal Hill, Limavady
174Pye Site, Creavagh Hill
175Rebro Station, Slieve Gallion
180UTV Transmitter, Koram Hill