Monday, 2 July 2012

Admiralty Experimental Station 4 – Unst - 1940 to 46

Very shortly after the start of WWII, Vice Admiral Sir James Somerville, who was in charge of the Directorate of Anti-Submarine weapons and Devices, witnessed a trial off the Suffolk Coast where a radar was used to attempt to track a surfaced submarine. The trial was successful enough to persuade him that radar could be a significant help in countering the U Boat threat. There were concerns about defence of the Home Fleet – 2 U Boats (U-18 & U-116) had attempted to penetrate Scapa Flow in WW1 and there were worries about U Boats and surface vessels entering the Atlantic in an attempt to cause disruption to Allied shipping. It should be remembered that, unlike modern submarines, most long distance travel by U Boats was done on the surface – the ability to remain submerged for long periods was limited – the crew members simply ran out of fresh air to breathe. Even with a snorkel, submerged time was limited and, though not large, snorkels could sometimes be sighted or detected by radar.
Somerville decided that a chain of 6 Coastal Defence U Boat Radar Sites should be built in the North of Scotland to help protect Scapa Flow and to provide a watch for U Boats/enemy shipping transiting between Shetland and Orkney or passing just north of Unst. The most suitable equipment available at the time was that planned for the RAF Chain Home Low (CHL)  & Army Coastal Defence sites. The Naval sites, which were originally developed separately from the CHL sites, were known as Admiralty Experimental Stations (AES) and they were each allocated a number. The site on Saxa Vord was AES 4, sometimes known as Saxavord (all one word) by the Navy. Radar production for all 3 services required a large construction programme, gun-laying radars, ship borne radars, radars against high and low flying aircraft were all needed. Priorities changed as the threat was continually re-evaluated and so, where there were similar roles, radar originally intended for one service, was sometimes diverted to another project belonging to a different service. Some equipment was interchangeable but not necessarily identical. The Naval CDU sites, whilst similar to the RAF CHL sites, sometimes had different equipment.
The map below shows where these Naval units were built. The ones at Dunnet Head and South Ronaldsay were primarily established to protect Scapa Flow. The 2 sites on Fair Isle and the one at Sumburgh were to provide surveillance of the waters between Orkney and Shetland. AES 4 at Saxa was to watch for traffic to the north. (Left click on pictures to nlarge).

The sites were constructed in 2 phases and the programme was carried out swiftly. AES 1, 2 & 3 (Sumburgh and the two sites on Fair Isle) were built in the first phase. The earliest to become operational was at Sumburgh which was opened in Dec 1939 – just over 3 months from conception to completion. The Sumburgh site was later moved nearly a mile northwards to Compass Head, above Grutness. The second phase included AES 4, 5 & 6, with the last one at Dunnet Head (AES 6) becoming operational in Dec 1940.
The daring raid of the U47, Captained by G√ľnther Prien, which penetrated Scapa Flow in Oct 39 and sank the Battleship HMS Royal Oak, is told in other places. Would the Coastal Defence Radars have made a difference had they been operational earlier– who knows?
It is tempting to try to recount the history of all 6 AES sites in Scotland but I don’t have the data or time to research the other 5 sites. In passing its worth mentioning that there was a later 7th AES built, but that was in Iceland. From here on this section will be directed towards AES 4 on Unst.
In early 1940 Vice Admiral Somerville and a small party studied a number of locations on Unst (incl Clibberswick – 160m/525’ ASL, an unnamed site about 1 mile west of Outer Skaw 132m/433’ and Libbers Hill 170m/558’) before selecting Saxa Vord as the site of the radar. At 285m/935’ the summit is the highest point on Unst and it was deemed to provide the best coverage for the equipment to be installed. A substantial track constructed in WWI, known locally as Whites Road, led up to near where the later RAF Saxa Vord Mid (or Ops) site would be built. It had been laid to enable a gun to be deployed to cover Burrafirth in case enemy shipping attempted to use the Firth. Between the two wars the local population used the route to access the plentiful peat banks on the hill. This track had to be extended and metalled before construction of AES 4 could commence.
As with the later RAF Station the “top site” was built in 2 parts. The lower part was where the generator and Rest Hut were located and the upper site, where the radar aerials were to be installed. There was no road between the 2 sites as there is now and so a 2ft gauge rail track, approx 120 yds/110m long, was laid between the 2 sites. Heavy material had to be winched to the upper level. Two buildings each 16’ x 16’ with a 10’ high ceiling were constructed as Transmitter and Receiver Blocks. Each of these Blocks had an aerial gantry built over them. The gantries were similar to the one in the photo below, though it is probable that at AES 4 they were initially built of timber:
Inside each of the blocks an operator had to rotate the aerial using apparatus similar to that which drives a bicycle except, in this case it was hand turned. The equipment was designed at Cambridge under the auspices of Dr John Cockcroft . Cockcroft was a very eminent scientist who was knighted after the war (1948) and went on to win the Nobel Prize for Physics in 1951.
At the top of the chain was a gearing system which looked like this:
The system had to be co-ordinated to ensure that the Transmitter Aerial was aligned with the Receiver Aerial. The radar beamwidth, at around 30 degrees, was wide so exact alignment, although much preferable, was not always essential. The Receiver Block also acted as the Ops Block and the radar display would have been a simple A Scope. It would have been from here that the Units single telephone line ran to the manually operated civilian exchange in the Haroldswick Post Office. From Haroldswick the calls had to be routed via normal GPO lines to the Naval HQ in Fort Charlotte in Lerwick. Whether afloat or on land, naval personnel were assigned to a “ship” for administrative and accounting reasons. During WWII the Royal Navy personnel on Shetland were considered to be on board HMS Fox (shore based establishment – HQ etc). The naval Coastal Defence Forces – Motor Torpedo Boats etc were considered to be aboard a Tender to HMS Fox called HMS Fox II. The establishment of the CDU would also have been considered to be a Tender to HMS Fox and personnel would have had cap bands saying either “HMS Fox” or possibly just plain “HMS”.
AES 4 became operational in September 1940 and was manned by Royal Navy personnel, with support from RAF and RCAF mechanics. One of the Canadians, Puss Valeriote, made a nostalgic return visit to Unst in June 2000. The Unit remained on the air for a short while after the war in Europe was over in May 1945. Its work had not been limited to searching for submarines/surface vessels – the radar had quite a useful capability for detecting airborne targets. By the end of 1940/early 1941 the radar was detecting shipping out to the radar horizon, 40 miles or more depending on the size of the ship, though for smaller vessels such as trawlers, ranges of 25 to 30 miles were normal. Aircraft below 10,000 were being seen at around 100 miles but performance of the early CHL was not very good against higher flying targets. By the end of 1941, following updates to the kit, ranges against airborne targets had increased considerably with ranges of 140 miles reported.
In the early years of radar, developments and improvements were taking place rapidly and so units, like AES 4, were frequently upgraded. The first major change at Saxa, in May 1941, was the changeover from 2 aerials to a single aerial. It would have been sited at the Rx Block. This change was made possible by the introduction of a new Transmit/Receive switch and new feeder arrangements for the aerial.
Evidence that the Receiver Block was extended to house the transmitter equipment can be seen in this much later picture, where the foundations of the extension are still visible to the right of the block.
Later in 1941 the performance of the radar was greatly enhanced when new valves (VT98) replaced the older VT58’s. Whilst I don’t have a photo of the interior of an AES Receiver Block the photo below is taken inside a similar sized building at the RAF Coastal Defence/CHL radar unit at Dover. The person on the left in the picture is Flt Sgt Wray and it gives an indication of the limited working space available.
In 1942 an even larger upgrade commenced. Work on new structure, known as a Combined Transmitter/Receiver Block or sometimes as a 1941 CHL Building, began. This was located half-way between the Receiver Block and the old Transmitter Block. It was much bigger; measuring 50 x 18 ft. RAF Chain Home Low sites would normally have a radar, like the one in the photo below, associated with the new type of Building (the small aerial on the building itself is an IFF antenna). Although I have not been able to establish its exact location, one of these aerials would have been sited very close to the new block at AES4.
However, the Navy decided that they would also use one of their own radars, a Navy Type 273. This radar was specifically designed for use against surface and low level targets and belongs in the group of radars the RAF knew as CHEL (Chain Home Extra Low). This decision was unsurprising as the detection of U Boats and enemy shipping was the main purpose of the Unit. This equipment was more usually carried on board ships. I don’t have a photo of one mounted on a 1941 CHL Building but photos of ship borne equipment follow:
The “tube”, made of Perspex, was known as a “Lantern”. Inside was an S band radar very unlike the RAF CHL equipment. The installation would have been like that shown in the next 2 pictures:
Because this was not a “standard fit” for the 1941 CHL Building, the one at Saxa had to be modified and a small extension was added to the north side. The following pictures, taken at much later dates, show the extension and the aerial mount.

To give you some idea of the difficulties faced I have included a photo of a similar radar to the Type 273, one of its forerunners the Type 271, on the back of a lorry. The problems of winching something that size and weight up a very steep slope on a 2ft gauge track is obvious.
The new equipment required more power than the generator on site could produce and so it was decided to lay a new power cable from the Power House at the RAF Skaw Chain Home site, 2 miles away, up to the top of Saxa Vord. The track of the cable can still be seen 60 years later – in the right light conditions the route taken stands out clearly, as in the Jan 2012 photo below:
The cable was removed long ago as part of an official contract and the copper recycled. In the following photo the ruins of the Power House can be seen with Saxa in the distance:
© Copyright Mike Pennington and licensed for reuse under this Creative Commons Licence
The work on the 1941 CHL Building, RN Type 273 and power cables took the best part of a year and the radar was actually ready a couple of months before the power could be connected. The new system became operational early in 1943. Regrettably, I have no photos from the inside of a Naval CDU/CHL 1941 Building. The next 3 pictures are of the inside of similar buildings on RAF CHL sites (no Type 273 Radar on the roof but some of the RAF sites had an earlier type of IFF aerial in a similar place, as seen in a previous photo). The main division of the building was into a Transmitter Room (one picture) and a combined Receiver/Ops Room (two pictures).
As seen on the right in the previous picture - at the really “sharp end”, the radar consoles would have looked like this - the range tube on the left and the PPI (Plan Position Indicator) on the right:
Whilst this work was taking place another structure was taking shape to the north-east of the Transmitter Block. A separate Mark III IFF (Identification Friend or Foe) installation was added to the site. The small building, known as a kiosk or cubicle was complete by Sep 1942, at which time the foundations for the 28ft mast were being laid. I’ve not been able to establish exactly when the actual equipment arrived on site, IFF Mk III was much in demand at this stage of the war and the allocation of IFF sets was prioritized between the various service requirements. The completed installation would have been like the one in the picture below – if you use your imagination and remove the trees!
Although the mast was removed at the end of the war, the kiosk remained until 1983.
To summarise the AES 4 structures, I have added a labelled extract from a May 1946 over flight photo but, unfortunately, the aerials and gantries had already been dismantled.
A different extract from the same over flight photo shows both the Heads site and the site where the generator and Rest Hut were located. The road down to Haroldswick is just where it is today.
The personnel involved with AES 4 were from various backgrounds. Much of the construction force consisted of local people and the ground defence of the site was the responsibility of the Shetland Defence Force, which included local people and members of the Royal Highland Regiment (Black Watch). The site was surrounded at first by a barbed wire barrier, to which a second was later added. There were occasional sightings of enemy aircraft and in 1941 a Heinkel III dropped a single bomb near the Transmitter Block – luckily no damage was caused. RAF Skaw saw slightly more enemy action but the uncertainty would have been the same whichever site you were on. The operations were run by the Royal Navy with, as mentioned earlier, technical back up from the RAF and RCAF.
There were few people on strength when operations started and the site had to be run on a 3 watch system, one watch at work, the second at the Rest Hut below the Tech site is case of inclement weather etc, and the third off-duty. The Navy had been lucky enough to take over a decent sized building at Haroldswick called Hamarsgarth; this was where the off-duty personnel were based. As time went on the number of personnel increased and the watch-keeping duties eased a little. By late 1942 Hamarsgarth could no longer cope with everyone and a Nissen Hut had to be built to cope with the overflow.
It was never a large complement, being commanded by a Lieutenant with a Chief Petty Officer as his deputy. As the only Navy Unit on Unst the staff were involved in the reception and provision of assistance to significant numbers of refugees escaping from occupied Norway in small boats – this could be quite time consuming and the fact that the refugees included women and children made the task more complicated. A small number of names of personnel who served a AES4 follows. Unfortunately there is little data about them, should anyone recognise the name of a relative I would be pleased to hear from them, or from anyone else with information about the unit;
Lt Orr
Lt Feachem
Chief Petty Officer King
Petty Officer Wilson
Bill Davidson
H Hawkins
Geoff Sleigh
Fred Walsh (Marine Driver)
Bill Stuart (from Pennicuik)
Whilst there were advantages with being close to RAF Skaw, inter-service rivalries occasionally surfaced – nothing has changed. Very infrequently there would be local dances or shows from ENSA (Entertainments National Services Association). Although ENSA had some very good and famous artists on its books they were spread thinly – leading to the acronym being changed by many servicemen to Every Night Something Awful. Despite the fact that most personnel were a long way from home a few of them developed an affinity for the islands in the same way that RAF personnel at the later Saxa Vord did.
After the Unit closed in July 1946 and the radar equipment removed, the site lay dormant for 8 years until 1954, when work on 91 Signals Unit/ RAF Saxa Vord and 2 new Admiralty Buildings commenced commenced. The old buildings were put to use as explained next.
The 1941 CHL Block was used as a Store and then as the Type 13 Workshop. After the Type 13 was replaced by the HF 200, the building was used to house Coastguard and Civil Aviation Authority equipment. The following pictures were taken of the 1941 CHL block in 1983/4, the first of the outside (note the brick construction) and the second of the interior.
At one stage the old CDU/CHL Transmitter Block was used by the Fire Section as a Smoke Building and a 40 gallon drum, converted to a rudimentary incinerator, can be seen in the centre of the following picture. I believe the antenna on the building belonged to Union Oil:
The CDU/CHL Receiver Block, shown below, had a more mundane after life as a store.
The IFF Kiosk is an enigma – I’m sure it was used but I’m not sure for what. So far I have 2 main lines of thought, either it was used by the RAF or, possibly it was used in anti – submarine trials by the Admiralty Research Laboratories or by NATO. Firstly, the pictorial evidence – the 3 photos which follow all indicate that something was mounted on the Kiosk. The first picture was taken in Feb 1961, just after the Type 80 reflector had been removed by gales - it shows a rectangular structure with a sloping top. It is possible that whatever was on the roof was damaged during the Jan ’61 gales and this structure has been lashed together to protect what was left.
The next picture was taken in the summer of 1963, whilst the Type 80 radome was being constructed. The same object can be seen from a different angle and a ladder appears to be attached to the Kiosk.

I have a picture which appears to show something on the roof of the Kiosk as late as 1978 – the photo is of insufficient quality to reproduce here. The third picture which was taken in 1983, just before the building was demolished, shows what appears to be part of some kind of aerial or turntable mount.

Secondly; the written evidence about the structure is largely conspicuous by its absence – especially on the RAF side. There is no mention of it in the RAF Operations Record Book (F540) – no maintenance, no down time, no calibration – absolutely nothing, (a major feat in these latitudes if it was technical equipment exposed to the elements)
On the Admiralty side there is no direct evidence which I have found. However, the Admiralty Building did have ducting for a radar and did have a Type 64 console installed. It is feasible that they had a radar on site for one or more of their trials and no evidence would appear in RAF records. It is also quite possible that it was equipment installed for use during the US/NATO submarine detection trials in the period 1960 to 63. This structure is, for me, one of the most interesting mysteries of the site! If anyone can shed light on the subject I would be extremely pleased to hear from them!
One other AES4 building was used by the RAF for many years with very few people knowing about it. During the construction phase in the mid 50’s, one of the lower site AES4 buildings was incorporated in the structure of the R10 Ops Block – maybe more of this in a future section!
I must acknowledge the assistance I have had in writing this section. A number of people have allowed me to use their research and material.

In particular I would like to thank:
Bob Jenner
David Waters
Ian Brown
Mike Dean
However, I accept responsibility for any mistakes and will be happy to make corrections where necessary.