Second World War Aircraft Direction Finding Part II – Locating the Sites

In the second part of this article I will pull together information and images from across a number of sources in an attempt to interpret some of the cryptic remains from what I believe to be HFDF sites across the country.

Siting the Stations

Great care was taken in May 1937 when two additional stations were sited in the Biggin Hill Sector. To reduce interference and optimise signal performance they sites had to be “in open flat country, free from obstructions such as buildings or clumps of trees and 200 yards from main roads and traffic.”1Signals Volume V, Fighter Control and Interception, Chapter 1, The Biggin Hill Experiments, pp15-16. Air Historical Branch, 1952 Before construction began the performance of each site was confirmed against long range aircraft and then calibrated using signals from closer aircraft. While relatively small patches of land were required for the new HFDF stations, this was at a time when the Royal Air Force was undergoing expansion and the pressure for purchasing new sites was huge. Such importance was placed on the provision of HFDF stations that the Chief of the Air Staff at the time gave personal attention to the issue “by all means possible.”

1937 was a key year for the deployment of HFDF stations, by the end of the year a number of Fighter Control Sectors in the south of England and around London had three HFDF stations each:

  1. Biggin Hill
  2. North Weald
  3. Hornchurch
  4. Northolt
  5. Duxford

It was intended that every Fighter Control Sector across the country would have three DF stations, but this was expected to take 2 years to complete.

HFDF Station Design

These sites were simple in construction and layout, with a common design being used across the country. There was the main HFDF tower; a 30 foot, octagonal wood clad structure, set in a brick blast wall for the protection of the radio operator who would have worked from the base. I have noticed two variations in the construction of this tower, one being the wood clad variant with wooden buttresses, as in the example at Southwold. There may have been a number of reasons for this:

  1. To support the structure in high winds. Many were located on the coast or on high points in remote areas.
  2. The tower may be hollow and lack internal support above the level of the walls, therefore external support must be given.
  3. I have read that the walls may have been filled with gravel for the protection of the crews. If this was the case, the walls would have been very heavy and would have needed external support. I do not rate this theory, not at least in the upper layers of the tower as gravel would have greatly attenuated (reduced) the incoming signal strength.
The HFDF tower at Southwold, a cropped image from the Imperial War Museum archives (reference A 26121). Southwold was a Naval Communications Station, and the large wood lattice masts can be seen in the background. It would not be unusual for HFDF sites to be colocated with other signals stations, and Southwolds location on the east coast was ideal.

There appears to be a variant on the wooden tower structure, and this is a light weight version which appears online when searching for HFDF sites. Most likely of the station at Hoxne, the four element directional antenna is exposed, and the tower may be clad in tarred felt. The site also lacks the recognised octagonal blast wall of others. Perhaps an early design.

Another site existed at Leckhampton Hill in Gloucestershire. In this post-war (circa 1951) aerial photograph, the tower can be seen without the wooden buttresses, and a variation on the tower design with a more open blast wall than has been seen with the existing snail enclosures, but the tower also does not appear to be wood clad. Of note, while the tower has been removed, the concrete base remains on the hill, as do the concrete sockets for the buttresses, suggesting at one stage they were present.

A rare closeup of the HFDF station on Leckhampton Hill above Cheltenham. This is the most complete image I can find of a HFDF site and appears to show a slightly shorter tower than other sites, it does not appear to be clad in wood, nor does it have the wooden buttresses of other sites. © Historic England Archive, Harold Wingham Collection (reference HAW/9390/08), reproduced on www.frontlineulster.co.uk with permission, reference number 7614.
Another low level aerial image, possibly from the Historic England archive of Hattingley (Farm) taken in 1947 showing the HFDF tower and ancillary building. The tower blast wall still remains, but the building has since been demolished.

Two images on Geograph have been uploaded showing the site at Nedge Hill, now demolished. The tower is the recognised wooden clad design, with wooden buttresses and a brick blast wall. Also in the images is a glimpse of the associated crew quarters and probable generator building.

From the ruins on site, as well as photographs from the two existing sites with their ancillary buildings still standing, I have been able to recreate the design of this building. It was constructed out of brick, with a concrete render and four brick buttresses, suggesting the walls were single skin. There appear to be two main living rooms, most likely with accommodation for a small crew of RAF personnel to maintain a 24 hour watch. To the rear of the building is a probable generator room to charge batteries or run the receivers in the HFDF tower. A single stove seems to have been provided, and with what seems to be a coal store on the side of the building, it is likely this was a solid fuel burner.

Based on a few images of the sites, I have produced a simple drawing of what the ancillary building would have looked like.

On most sites, all that remains today is the brick blast wall, or the concrete base of the HFDF tower. With eight equal sides, and associated buttresses, there was a gap to allow the operator to enter the tower. Given the side of the tower it was likely only one operator would have been required and they would have worked the receiver set from ground level, behind the protection of the blast wall.

An equal sided octagon brick blast wall with narrow entrance gap, the wooden towers have long gone, but the concrete sockets for the wooden buttresses remain, as do steel bolts inside the enclosure to secure the wooden tower.
There is also a second configuration of HFDF tower base. One site with this form of base is at Halnaker Hill. In this configuration there do not appear to be external buttress foundations, but evidence of wooden post holes internally. Given that there seem to be two types of HFDF tower, this may be a base for the lightweight tower.
The site on the headland at Scarborough has been captured in this Britain from Above aerial image taken in 1947. With multiple structures on the headland, the HFDF tower is clearly identifiable. The brick blast wall appears different than other designs.
A close up of the Scarborough HFDF site on the headland. Britain from Above image EAW005716 taken in 1947.

Ballyhalbert HFDF Site, County Down

The HFDF site at Ballyhalbert, County Down, was located approximately 500m south of the airfield at RAF Ballyhalbert © Google Earth

Garway Hill HFDF Site, England

The single tower site at Garway Hill in Herefordshire appears to be unique as the two elements of the site were surrounded by an earth bank and ditch, possibly a fire break if the area was covered in thick vegetation. © Google Earth

Hillquoy HFDF Site, Orkney

The Hillquoy HFDF site on Orkney. The characteristic octagonal blast wall can be seen in the centre of the image, with the technical building to the south west approximately 100m away.

Leckhampton Hill HFDF Site, Gloucestershire

This low level aerial photograph of Leckhampton Hill Fort, above the town of Cheltenham is from the Historic England archive and dates from around 1951. The image shows a rare glimpse of a HFDF station (image centre) and the associated crew quarters building to the right. © Historic England Archive, Harold Wingham Collection (reference HAW/9390/08), reproduced on www.frontlineulster.co.uk with permission, reference number 7614.

Pocklington Fixer Station, Yorkshire

I was sent a series of images from Geoff Harris who contacted me through the website about a previously unknown station at Pocklington in Yorkshire. They show the RAF personnel of the fixer station standing outside the buildings on the perimeter of the airfield. The first image from around 1943 they are in front of the accommodation building, and in the second image they are in front of the blast walled direction finding enclosure. Geoff also includes a RAF aerial photograph from 1946 in which the station is visible. But what is apparent from these images, is the blast wall enclosure is square, and inside it appear four masts; what I believe is an Adcock direction finding array. A variation from the evidence I have seen at other stations, and something I will investigate further.

Multiple Tower Sites

There are a number of sites identified that have more than one HFDF tower, some as many as four towers located around the central crew admin building. This may have increased the capacity of the site to track aircraft in the area, and given their location in the south of England this is likely. With each HFDF station being able to tune into a single frequency, this would facilitate tracking of a fighter squadron (one time slot per section within the squadron, up to four). With the air battle raging overhead, it must have been necessary to have the capacity to track more than one squadron at a time, so the construction of multiple receiver towers at single sites.

The multiple tower site at Habchester in Northumberland has now been totally demolished, but had three towers approximately 200m apart in a similar formation to the other multiple tower sites.
Wittserham HFDF site in Kent. With four towers visible it is possible this site was equipped to track up to four squadrons of fighters and was expanded as the need developed. This image is from the 1946 aerial survey of the UK by the RAF. It appears that at this time only the southern most enclosure has a tower still standing, and it does not appear to have the wooden buttresses. © Google Earth
The site at Halnaker Hill in West Sussex also had multiple enclosures. There are three still visible, two centrally (also note the windmill and its shadow) and what appears to be a third HFDF enclosure foundations only to the south west in the adjoining field. The structure to the north is what appears to be an HFDF enclosure, capped with concrete. © Google Earth

Mapping the Sites

Using a combination of sources I have been able to identify 26 extant or sites with elements still standing and 10 further demolished sites. Of the 36 sites with visible remains, only 3 appear to have their associated support building still present. The octagonal blast walls exist in many of these, but in some only the concrete base remains. I am sure there are more sites that I have not been able to identify and the list may well grow in the coming months and years. Thank you to those of you who have submitted sites not previously in this database.

The main problem with identification has been inconsistent classification of the sites, and the use of a variety of terminology. Perhaps some sites had double roles, especially given that the pip-squeak huff-duff technique appeared to cease in 1942, some may have been adjusted for other RDF work or been incorporated into the Y-station network of wireless intercept stations. Perhaps all DF stations fulfilled multiple roles during their operational life.

You can download a KML file for these locations from the download section.

Conclusion

These unique sites spread across the country were short lived but their importance can’t be underplayed. They filled a vital gap in capability to not only identify but guide our fighters towards the enemy aircraft. It was a rudimentary system devised when manpower was stretched, and equipment was limited, and while the role of monitoring the HFDF stations would have been relatively safe and away from enemy bombing, it must have been solitary and tedious at times.

I would like to visit and record as many of these sites as I can in an effort to further document and understand them. Keep your eyes peeled, and I hope you can make use of the list of locations I have already been able to record.

Amendments since publication

  • Multiple tower site at Minster, Kent added. Information from the Pillbox Study Group MikeofDorset, visible on 1946 aerial images. All structures now removed.
  • Scarborough HFDF image obtained from the Britain from Above archive confirming the presence of a site on the headland. Added to database.
  • Further sites identified from the extended Defence of Britain archive, listed as removed but with remains still evident: Duxford and Lyme Regis; no trace of sites at Whaddon, Farningham, Hyde, Southwell, and Weston; with possible sites at Inverness and Portsoy.
  • Site at Shropham added, most likely serving Snetterton airfield. All remains removed.
  • Photographs of the site at Ballyhalbert added.
  • Millfield HFDF site location discovered and submitted by J Towill.
  • Bury Down site added thanks to a contribution on Facebook by C Counter.
  • St Davids site added, accidentally omitted from first version.
  • Coverack site identified by S Davies on Facebook.
  • Thank you to Ian Brown to has contributed valuable context and information to the operation of these sites, as well as highlighting a number of new sites to the database.
  • C Jackson identified the site at Hoxne as a FV10 equipped VHF direction finder installed at Royal Naval Air Stations.
  • Geoff Harris submitted evidence of a now removed site at Pocklington.
  • I visited the site at Hillquoy on Orkney. An album has been uploaded to Flickr and linked to this page.

Download

You can download a copy of a KML file for all of the fixer station locations featured in this article. The KML file is compatible with GPS handheld units, mapping software and Google Earth.

Contribute

If you have any information to contribute to this article, please get in touch.

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  • 1
    Signals Volume V, Fighter Control and Interception, Chapter 1, The Biggin Hill Experiments, pp15-16. Air Historical Branch, 1952