Relocatable Over The Horizon Radar (ROTHR) Deployment in the UK

[JFC Fuller]

Reading Friedman's Fighters over the Fleet I came across the statement that it was planned to install a ROTHR system in Scotland to cover the Norwegian Sea (a statement Friedman has made in several of his books over the years), so I started seeing if I could find out exactly where in Scotland the system was intended to be deployed. However, within the UK I could only find reference to an intended installation in Pembrokeshire, at the south-western tip of Wales. The best available source online is an article in the July 1990 Electronics World Magazine. Key points:

• US/UK project with the UK paying 90% of the £10million development (I think they mean construction) cost, US to pay $90 million for the radar and computer system
• Receiver site and operations centre to be at Brawdy (though the Secretary of state for Defence told Parliament it was St Davids, both St Davids and Brawdy were MOD property until 1992 and are within 7km of each other)
• Transmitter location is not given but is assumed to be over 30 miles way
• Range is at least 1,800miles with an azimuth of 63 degrees focussed on the Baltic
• It would transmit between 2 and 28 MHz at a leak power of 200kw
• The receiver aerial would be 2,590m long and consisting of two rows of 372 supporting poles and 43 equipment shelters
• The locals didn't like the idea

I assume the installation was never built and the plan was abandoned sometime between mid-1990 and 1992. Does anybody have any further information on this? Is Friedman referring to an earlier plan that was abandoned or was it intended to operate two ROTHR systems in the UK, one looking at the Baltic and one at the Norwegian Sea? Or is the claim that the Pembrokeshire facility was to look at the Baltic incorrect?

 

[Yellow Palace]

I assume the installation was never built and the plan was abandoned sometime between mid-1990 and 1992. Does anybody have any further information on this? Is Friedman referring to an earlier plan that was abandoned or was it intended to operate two ROTHR systems in the UK, one looking at the Baltic and one at the Norwegian Sea? Or is the claim that the Pembrokeshire facility was to look at the Baltic incorrect?

According to this record from Hansard, St Davids was to be the transmit site and the receiver to be Blakehill radio station in Wiltshire. Brawdy was explicitly ruled out as unsuitable, along with about 160 other proposed sites. As is normal for proposals to build things anywhere in Britain, there was a lot of opposition. By May 1991 the plans had been cancelled due to cost.

As I understand it, OTH radars aren't really suitable for looking poleward and/or high latitudes, due to interference from the magnetosphere. Presumably this would have put paid to any North Sea proposals. Possibly Scotland was initially floated as the site (there were questions asked in Parliament about OTH radars by the Member for the Western Isles in the early 1980s - this might be a clue) but further development of the proposals made Wales a more suitable site.

This was also around the same time that there were proposals for an ELF transmitter to be built in Scotland (trial site in Glen Garry), so the two projects may have been conflated to some degree.

 

[DWG]

One thought that pops to mind is that a system based in Wales/Wiltshire is somewhat less exposed to attack (on control centre buildings) than one in Scotland. Any attacker has to plough through half of UKADGE to get to it, which might be a worthwhile trade-off vs range.

 

[Grey Havoc]

If I recall correctly, the receivers for the United States' late 1980s USAF (fixed site) OTH radar system had to be at least 50nm from the transmitters. A similar constraint may have applied in this case.

 

[Yellow Palace]

If I recall correctly, the receivers for the United States' late 1980s USAF (fixed site) OTH radar system had to be at least 50nm from the transmitters. A similar constraint may have applied in this case.

30 miles was the planning figure for the US Navy's ROTHR - itself a fixed site system, just one that had been designed to be disassembled, packed into 600 shipping containers, and moved to another site if required.

Perhaps a little off the topic, but a little on ROTHR planned deployment...

After the trial system in Virginia, three production sets were ordered, with an option for a fourth. Proposed sites for these were in Amchitka, Guam, the UK, and Virginia. Ultimate deployment of twelve sets was planned; a second site to cover the Caribbean and Central America was one of these, which ultimately became the Texas site, and the USN's Pacific Command planned for installation of five ROTHR sets to cover the Western Pacific - two in Amchitka and three in Guam. That's still four locations not accounted for - possibly three if the Puerto Rico installation was one of the originally planned sites.

There's a Soviet intelligence assessment on DTIC (unfortunately I didn't bookmark it) that refers to attempts to persuade the French government to allow an installation in the south of France that would cover the western Mediterranean and part of North Africa, which might well be one of them. It would certainly make sense for further installations to be planned to cover the Mediterranean and eastern Atlantic.

The first Amchitka installation took place, using the prototype set, and site selection was under way for the second Amchitka and the first Guam set; the site selection reports give some indication of the technical requirements for the system and sites. Presumably the prototype in Amchitka would have been replaced by a production set in due course if the project had gone ahead. The Guam site selection report specifically identifies that the UK installation would only be one set.

In the course of digging, I've also turned up some interesting stuff on the USAF's fixed-site OTH radars, but that probably warrants a new thread.

 

[Yellow Palace]

A few interesting notes to add to this discussion. First, Google Books now hosts a copy of the MoU signed between the US and the UK for the ROTHR installation. No real details beyond a statement that the radar was intended to be north-facing and some indication of the amount of equipment involved, but interesting all the same.
https://www.google.co.uk/books/edition/Defense_Relocatable_Over_The_Horizon_Rad/2DbWI06bWqYC
Secondly, an article on the RAF Blakehill Farm website discussing what seems to have been called Project POTEEN.
https://www.rafblakehillfarm.co.uk/poteen-an-tp-s71-blakehill
Key points here are

• The radar was to be installed with a transmitter at St Davids and a receiver at Blakehill Farm, as noted above. The size of the receiver antenna woudl require some land acquisition adjacent to RAF Blakehill Farm.
• The radar was to be north-facing to provide surveillance of the Norwegian Sea.
• The unit would be under command of an RAF Wing Commander, with about 120 personnel divided etween the US and the UK.
• It was expected to become operatinal in 1993 or 1994 for a two-year evaluation phase, after which a decision would be made on whether to make the deployment permanent.

If one assumes the centre axis of the radar beam is directed perpendicular to the line between the two stations - and that's a big 'if', then coverage of a TPS-71 northwards from these stations is pretty much spot on for the Norwegian Sea. In principle that provides coverage from the Kola Peninsula all the way to the GIUK gap, as seen using the Great Circle Mapper.

It's not hard to see why this kind of coverage would be of interest to the US Navy. The southerly location also means that the minimum range gap inherent to the OTH-B principle is covered by the UKADGE radars at Saxa Vord and Benbecula; these were upgraded to the same FPS-117 radars installed in Iceland as part of the North Atlantic Defense Systems. I don't know if there was a plan to similarly upgrade the radar in the Faroes, but I'd be surprised if not.

 

[Wingsy123]

Hi Yellow Palace et All,

Glad you found the Blakehill link relating to the ROTHR. There is also another “page” at https://www.rafblakehillfarm.co.uk/blakehill-gchq-radar-years which looks at the use of the site itself, including the ROTHR testing. The link you already have looks at “Poteen” in particular. It’s just the way we decided to set up the website.

Just a bit of clarity - in no particular order. The name “Poteen” is the US project name for the UK ROTHR (see the US DoD Appropriations document page in the link you found) and there is much discussion over the years as to how the system sites around the world were going to be chosen and then changed(!) – before ROTHR was finally canceled. Re the UK ROTHR, the equipment earmarked initially was P(roduction)3 but turned into P2, initially planned for Guam, when, in Feb 1990, Admiral Hardisty USN announced that, due to problems in Guam, the 1st Guam ROTHR (P2) was being “queue-jumped” over to the UK bringing Poteen forward while they sorted out the “issues” in Guam. P1 was to be tested in Virginia before being re-deployed to join the Prototype system which, had by then, already moved to Alaska from Virginia.

While a total of 12 ROTHR's were planned, in the end, only 4 were built – the prototype (which ended up in Alaska) and 3 production systems which were planned for Guam, the UK and as a 2nd in Alaska (via testing in Virginia). I’ve pretty much tracked the entire story via the DOD Appropriations from 1982-1992 though there were various changes as things ebbed and flowed! Only a few sites had been formally identified by the time the ROTHR programme was canceled (a lot of work was going on to see if Japan would host one or, possibly 2, systems – so that’s maybe 7 systems accounted for including a 2nd for Guam) – and it was definitely still very much "work in progress" to identify homes for all 12 systems – 13 if you count the Prototype which, I suspect, would have been upgraded to P-status at some point.

Certainly I never saw Texas/Caribbean mentioned anywhere – so if anyone can identify any sources where this is discussed in the 1980’s as part of the Military ROTHR network I’d be interested to find out more. The USAF were planning a 3rd 2-sector OTH(B) to cover the Caribbean in addition to the initial 2 x 3-sector OTH(B) systems (the WCRS and the …… wait for it …… ECRS) OTH(B)’s, neither of which ever fully came on line. With a further OTH(B) looking South (probably to be called the SCRS!), there would have been no need for a military ROTHR in Texas. Maybe they used the planned SCRS OTH(B) sites for the anti-narcotics ROTHR when everything changed at the end of the Cold War. That makes sense - but not to base a Military ROTHR in Texas.

As mentioned in a previous Post, the “UK system” (or should I say, the “1st Guam system (P2)”!!!) finally ended up in Texas where it is still working today in an anti-narcotics role looking South over the Gulf of Mexico. As I say, from my research, Texas only came into the ROTHR equation after the demise of the military requirement at the end of the Cold War – it (and then Puerto Rico which got P3) were, as far as I can see, never part of the planned Cold War ROTHR network. The 3 production ROTHRs (finally P1 – Virginia, P2 – Texas and P3 – Puerto Rico) became part of the world of anti-narcotics (who have their own Budget) and they remain in that Budget with $89M allocated for FY2026. The Prototype was mothballed in Alaska and finally scrapped in situ in 1998. To take the story to the end, the ROTHR’s successor, TACMOR, is due to be rolled out in Pilau to cover China and work has started on the Rx site at least. However, I can only find $25M for TACMOR Infrastructure in 2026 ……. I can’t find it mentioned in any Equipment Procurement budgets for 2026. Maybe it’s been canceled by Trump………….. and the $25M is to simply to restore the site work done to date back to Rain Forest?

Re “line-of-shoot” for the UK ROTHR, the alignment of Blakehill and St Davids is more by co-incidence to be honest. The alignment of the arrays is what counts and, as you can see from the other Blakehill Farm link, the early trials involved Tx sites in Hants and then Northants. The test array at Balkehill Farm (first LAPSE and then LAPSEE) was aligned with the required “line-of-shoot” – that was really the key to gaining the coverage that John Lehman, the then US Secretary to the Navy wanted, to cut off any breakout of the Soviet Northern Fleet. Your “Great Circle Mapper” is useful to show that and, again, your assessment that the ROTHR will fill out past the NADS centimetric Radars is spot-on and is actually mentioned in the DoD Appropriations page in the link I mentioned earlier. Some bits are redacted but that’s what it covers!

I have never seen the plans of proposed site of the main Rx array at Blakehill as Poteen was canceled before detailed site survey worked kicked off but the use of common sense (dangerous I know!) positions the final array as being a bit further into the airfield to minimise the amount of extra land which would be required as indicated in the airfield plan. I have no idea where the Ops Room would have gone but it is quite a substantial building looking at the other ROTHR sites and is usually not far behind the Rx Array so would have occupied the Southern part of the airfield at Blakehill Farm.

Staff wise, it was to be a multi-national RAF Signals Unit (SU) with UK and US personnel working at both St Davids (quite a small outpost – I think it was only about 10 people) with the main Ops Site being at Blakehill Farm with about 120 people in total. The Ops Site would also provide remote-control for the Tx at St Davids and the feed-in to the UKADGE and NADS. The SU, based at Blakehill, would have been headed by a Wg Cdr. The demise of the Soviet Union sounded the death-knell for Poteen with “our” UK kit being redeployed (yet again!) to Texas as I mentioned.

Anyway, hopefully this is of interest and happy to answer any further questions if I can. Vince Povey, the main guy who maintains the Blakehill Farm website and the memories of the many people who were based there is really pleased to see his site being used!

Cheers, Chris