Was there a secret intercept station at Divis?

There are many elements of operations in Northern Ireland that will remain secret, and rightly so. But as time moves on historians, academics and enthusiastic amateurs will slowly uncover details which I am sure all but a select few would have had exposure. As the saying goes “a little knowledge can be a dangerous thing” and perhaps the assumptions we make based on scant evidence are just that. Never the less, without speculation we may never piece everything together.

At the beginning of the Troubles, intelligence was so poor that the Army rounded up for internment many innocent people, based on inaccurate or old information, in an act that backfired severely. But the security forces have learnt lessons which have made them one of the most formidable intelligence forces in the world. In recent years, there has been so much electronic surveillance, videoing, telephone tapping and bugging that it is a wonder that the Northern Ireland population does not glow in the dark.

An article from the Independent newspaper titled A province that is full of spies and their gadgets, published on Wednesday 21 September 2011 © Unknown author at the Independent Newspaper

The purpose of this article is to explore the idea that there may have been a secret radio intercept station on Divis Mountain that exploited a wireless telephone link between Londonderry and Belfast, and the Republic of Ireland.

A little bit of background

The established military communication site on Divis Mountain. Image taken 2008 © Frontline Ulster

On top of Divis Mountain is a military relay station. Its presence is well known and its importance well documented. I have even written a brief article on my visit there. The archives record that between March 1970 and May 1970 Royal Engineers from 30 Field Squadron constructed a communications relay station on Divis Mountain. The site was exposed and in the early days had little infrastructure. So much so that the radio equipment was initially housed in elephant shelters (temporary sheds) and supplies had to be flown in by helicopter until an access road was installed. Throughout the operation the site developed into more than a relay station and became key to the military communications network. Decommissioning of the site began in 2004 when teams from the Royal Engineers started removing dannert wire and concrete blocks, but demolition was not completed until a few years later. But it may surprise you to learn that my speculative intercept station was not in fact the well-protected military communications site, but the innocuous looking agricultural building at the bottom of the hill.

This is the view of Divis Mountain from the Divis Road. On top of the hill is the established military communications site known as Divis Key Point, to the right in the dip is the huge BBC television transmitter, and in the centre of the image below the hill is the innocent looking range hut © Frontline Ulster

In a previous article about the firing range established in this area in 1943, I explored what I described as a target shed or range hut which was adjacent to the range. And while I don’t doubt that this was the original use of the building, the concrete block extension gave me cause for further investigation. It had no practical purpose connected to the range that I could establish, and there were tantalising features that made me think it may have had a more serious security purpose. When I last visited the site in 2016, and when I first noticed the unusual features.

Update March 2021: Reviewing some documents obtained in a visit to the Royal Engineer archive in Chatham, I came across a1972 operational report by 8 Field Squadron who were deployed on an emergency tour to Belfast between July and September 1972. Task 771 completed by 59 Independent Commando Squadron Royal Engineers was the erection of a Nissen hut on Divis Mountain. It is possible that this hut was constructed at this time.

Gallery

As an ancillary range building all that is required is an open space for the storage of targets or to give shelter to waiting troops. The features this building has do not fit this role. It was only when I came across a website on the history of BT microwave networks that my theory about the use of the building started to gain traction.

Forming a theory

Situated 430 meters away from the range building is now a guesthouse, and at the time of my visit when staring out of the large apertures of the building I could not see anything of remote interest that may explain its purpose. However before redevelopment, it was the site of Standing Stones radio station; a British Telecom owned and operated microwave station, carrying television and telephone data.

An image (cropped) from Standing Stones radio station from the BT archives, taken on 22 July 1969 © BT Heritage TCB417/E 40413 (view original record)

The above image from 1969 shows a single microwave dish on the tower pointing south, the main direction of this north-south microwave link. In the late 1970’s a further link was added1Website: http://dgsys.co.uk/btmicrowave/ which pointed towards another hilltop site at Mullaghmore, 59km away. This second dish provided a Belfast – Londonderry link for TV and telephony. It was when looking at the map of this microwave network that made me look at the range building with a more sinister perspective; the position of the range building and orientation of the possible equipment may have made it possible to exploit both the Londonderry and the south links.

Assuming the microwave beam has a spread of 1 degree either side, that would result in a beam around 2km wide at the 60km range between Mullaghmore and Standing Stones. The range building is ideally situated and at the right elevation to receive the signal with a high level of integrity. Base image © Google Earth

In fact in the 1990s it was revealed that a secret site at Capenhurst in Cheshire, England was positioned in the beam of a microwave link carrying telephone calls between the Republic of Ireland and England, and it is speculated that this tower was exploiting that signal and the calls carried in it.

A representation of the Capenhurst site which was reported as intercepting Irish telephone traffic that originated from under sea cables and was subsequently transmitted over microwave link from North Wales. Image copyright © 1999 Richard Lamont

Does the evidence support the infrastructure?

The first issue to address is the requirement to intercept this data. The 1970s were a difficult time for Security Forces in NI, at times I am sure the feeling was that the conflict was out of control. It was also in this decade when a major series of permanent building projects took place, with many of the temporary locations being rationalised, upgraded and fortified. As well as the overt presence, was a large intelligence gathering effort; and this must have included the interception of domestic telephone lines. With the Mullaghmore link broadcasting a large number of phone calls from Londonderry to Belfast (and beyond) it must have been a priority to have access to this. As one caveat to this whole article; I have no evidence for this theory other than speculation. I am sure at some stage information will be released into the public record that confirms or disproves my theories. Until then, I’ll keep digging!

(H)is unit in Derry, known as ‘North Det’, had electronic intelligence that the Real IRA was moving an explosive device out of the city to be used in an attack on an unspecified military security target in the north of the province.

An extract from an article in the Belfast Telegraph about a book released in 2016 by an ex-soldier Sean Harnett. Electronic intelligence could have come from many different sources, perhaps it was disclosed in a phone call from Londonderry that was carried on the Mullaghmore – Belfast microwave link?

Location

A range was established at Divis in 1943, many years before the radio station that was constructed in 1969, and before the Mullaghmore link in the late 1970s. While the corrugated iron range hut may have existed from the early days of the range, the concrete block annex was likely constructed at a later date. It may however have been constructed in 1972 as records from the Royal Engineer archive suggest.

Looking at an Ordnance Survey map of the site and two buildings confirms the suspicious alignment of the pair. It may make sense of the misaligned apertures within the range building and the mounting bracket tucked into a corner © Crown Copyright (Ordnance Survey)

From evidence I can find online, it is desirable to position any intercept equipment in the middle of a beam. This is certainly the case for the Capenhurst site. With the Standing Stones radio station acting as a conduit for calls between Londonderry, Belfast and the south of Ireland it is possible that while it does not sit in the middle of the beam for both ends of communication, it appears to catch overspill from both incoming and outgoing calls .

Building plan

With this intent in mind, I revisited the plan of the building that I had drawn for my site visit report in 2019. The offset apertures and mounting of a pole in the corner of the room had always been a mystery to me. But working from the beam paths on Google Earth and now knowing the location of the Standing Stones radio station, this configuration makes sense. It allows the largest possible aperture to receive any overspill from the Mullaghmore microwave link.

A plan of the interior of the range hut annex. By revisiting the plan and looking at the alignment of the apertures and the positioning of the mounting pole in the corner the purpose makes a bit more sense. Not to scale.

As for the large apertures, it is likely that these didn’t have glass but a fibreglass radio transparent material panel in them. It is fibreglass that most radomes and radio antenna enclosures are made of. A fibreglass panel may explain why the external of the building has been painted white; to help disguise the large panel that would have otherwise looked out of place on a military range building or agricultural shed.

Physical security

The first room is very narrow, it seems to serve no other purpose than being a buffer to access a second door. This door is steel and has a very secure locking mechanism.

With such a strong door and mechanism fitting to an otherwise innocuous building, it only begged the question to be asked; why?

Not only one door, but two. While the site was relatively isolated, there was a section of armed soldiers nearby manning the Key Point on top of the mountain. It is likely they did not know the purpose of this building, but would have been alerted to any intruder by alarm, to which they could respond. With two doors on the inside, and two apertures suggesting a double skin on the outside, these would certainly have delayed any intruder sufficiently for a response to be mounted.

If indeed there was sensitive interception equipment in this unmanned building, keeping it secret would have been the highest priority.

Conclusion

Besides the Capenhurst tower, communications between the Republic and the north were intercepted by facilities in County Armagh. These sites, including a station at Drumadd Barracks, Armagh intercept microwave radio and other links between Dublin and Belfast.

Bugging ring around Ireland, Duncan Campbell, 25 July 1999

Interception of this nature was, and is still nothing unexpected for security forces in Northern Ireland. As the microwave network was expanding in the 1970s and 1980s, it seems that significant efforts were made to exploit these new sites, and it is possible that Divis was one of those. If correct, then it is likely that this site played its part it preventing many deadly attacks on the population and security forces. I am sure there are opposing civil liberties arguments to be made, but I am afraid they are not the scope of this research.


Thank you for reading this article on a rather different theme than I am used to, but I am sure form the evidence presented that you will have made up your own minds. Regardless of the outcome, this is just one fascinating and compelling piece of history, the truth of which may never be understood.

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