Island Hill Direction Finding Station

It is well acknowledged that signals intelligence, or SIGINT, was one of the tools that allowed the allies to shorten the length of the Second World War, and Northern Ireland played a crucial part in this battle through the Radio Security Service (RSS) interception and direction finding (D/F) station at Gilnahirk. At the end of the war this work was scaled down, but continued under the auspices of the newly formed Government Communications Headquarters (GCHQ) until the site finally ceased operations in the 1970’s. What is not so well known, is the operation of a high frequency D/F station at Island Hill, less than 5 miles from Gilnahirk.

The definitive history of the Gilnahirk site, The Spies at Gilnahirk (George Busby, 2016), contains little information on the Island Hill site, but does say when it may have been operational and in what capacity.

While the work of the D/F station may have continued uninterrupted after 1945 (…) towards the end of 1948, beginning of 1949, the underground cabin (author: this was the underground direction finding facility at Gilnahirk) was abandoned.

This high frequency direction finding facility was moved some seven miles across country to Island hill on the shores of Stanford Lough outside Comber. Working above ground everything was contained within a wooden hut placed just above the ground, but sitting on a mat of coiled copper wire.

Chapter the Cold War, p110-111, The Spies at Gilnahirk, Busby, 2016.

Both Gilnahirk and Island Hill stations ceased operation and were abandoned in June 1978.1

Locating the Site

Attempting to find a secret facility that was operational between 1948 and 1978, that closed 50 years ago, would be difficult. The true purpose of sites is not often recorded on maps, and aerial images would be far and few between. The site is recorded as wooden hut, in what is a rural area, making identification even harder. And the chances of surface remains being present today are slim. But ever determined I trawled my usual research websites.

Online search

An online search for anything related to Island Hill proved fruitless. The main reason I believe is the lack of information regarding this site available online. One of the more conspiratorial websites has both Gilnahirk and Island Hill listed as a “GCHQ (eavesdropping) sub base,” but the anti-establishment overtones and lack of further information mean this is definitely not worthy of use as a source!

PRONI Historical Maps

For all sites in Northern Ireland, the historical map viewer is an early source. While full region coverage of all map series is not available, there is sufficient to at least confirm place names and see the landscape as it would have appeared in the period of interest.

Locating Island Hill on the Ordnance Survey (OS) 1:10,000 series maps wasn’t too difficult, it is a small hill to the south west of the town of Comber, and on the shore of Strangford Lough. But no sign of a D/F station. This edition of map dates from around 1986, and if the station closed in 1978, it is likely that all signs had been demolished by then.

Frustratingly, the fifth edition OS maps (up to 1963) were not available for the Island Hill area. So I decided to try a different resource.

Britain From Above

An excellent online resource run by Historic England, but including thousands of Irish aerial images, is the Britain From Above website. Collating aerial photographs dating from between 1919 and 1953, and geolocating them on an interactive map, it’s possible to find images taken for commercial purposes nearly 100 years ago that include military or other sites in the background. This is what I was hoping for in the search for Island Hill.

At first glance on the map, there were no images in the vicinity of Island Hill (to the bottom right of the shore in the image below). There were however a cluster of images taken in 1952 of the construction of a new sewage treatment works. Worth a look.

Wait! What’s that …

On looking through the images, I noticed a peculiar fenced compound in the background of image XAW045169. This is not an area I would consider to be Island Hill, but it had all the hallmarks of being a communication site.

Taken over Strangford Lough, the camera is pointing south west.

When zooming in to this 1952 image it becomes clear that this has a high likelihood to be the illusive Island Hill D/F station I was looking for, having been constructed only 4 years earlier.

The detail in the background of image XAW045169 from Britain From Above shows what is clearly a D/F station, with operational buildings and 4 large masts.

The site appears to consist of more than a wooden hut at this stage, but I estimate five buildings can be seen in the image, inside a square compound with four pole masts in the corners.

Revisiting the historic maps from PRONI, and I was able to locate the D/F station and compound on the fifth edition maps of the area. On the map, oriented north to the top, the square perimeter fence is distinguishable, along with the operational building in the centre, and the ancillary buildings around the edge. What is unusual is the omission of the four masts in the corners of the site, if still standing when the map was drawn, I would have expected them to be included. The pump house at the rear of the buildings has been marked as such on the map. Access to the site appears to be off a single track lane across the fields to the north. This is now the A21 Comber – Newtownards dual carriageway.

The small D/F station at Island Hill can be seen on a single edition map, the Ordnance Survey Fifth Edition (1919 – 1963). Crown copyright 2020

J 48081 70026

The grid reference of the Island Hill D/F station

This farm track was once the access road to Island Hill D/F station.

Interpreting the Site

With only a single grainy aerial image to go on, the interpretation of the site will lack some detail. However, I think I am able to identify the main features of the D/F station.

A similar site has been captured in a 1946 aerial photograph. This site, also a D/F station was one of three around the village of Sutton valence in Kent. The layout is remarkably similar to Island Hill; four masts with a central operational building and a number of small ancillary buildings.


Locating the Island Hill station has been a positive achievement. From what I can ascertain the location has not previously been published, and little is known about the operation of the station. I am not clear on if the station was used solely for the D/F of military targets such as submarines or shipping, or if (as the many conspiracy sites would have us believe) that the station was used during Operation Banner for the interception and “eavesdropping” on security targets in Northern Ireland. I believe the former was the main operational role of this site.