At the beginning of WWII the UKs Chain Home RDF system
stretched along the south and east coasts of England and up the east coast of
Scotland. However, the most northerly station was at Netherbutton, near Kirkwall, in Orkney and
the equipment there was designed to look primarily to the south-east. In the
early part of the war, with all three services having strong operational
requirements for this technology, manufacturers of RDF (radar) components had difficulty
keeping up with the demand and it was necessary for priorities to be
established. Nevertheless, the allocation system had to be flexible to meet new
needs. In April 1940 German forces invaded Denmark and Norway leading to the
decision to expand radar cover in the Northern Isles.
From the Shetland perspective this meant the immediate
formation and dispatch of a radar unit to Unst (No 3 Transportable Radio Unit -
http://ahistoryofrafsaxavord.blogspot.co.uk/2013/01/the-first-radar-on-unst.html). It was also decided to build two
permanent sites in Shetland, at Noss Hill at the south end of the Shetland
Mainland and at Lambaness, in the north of Unst. Both of these sites would
become operational as Advance Chain Home (ACH) stations, quicker and simpler to
construct than the full Chain Home (CH) stations, whilst work on the more
substantial Final CH equipment and structures continued. The site at Lambaness
on Unst (RAF Skaw) will be described in later sections, this article will be
confined to RAF Noss Hill.
Noss Hill is just south west of the Loch of Spiggie and
about 3 miles north-west of the airfield at Sumburgh. The summit of Noss Hill is
367ft above sea level and, when
construction began, there was already an operational Navy radar (AES1), mainly
looking for surface plots, at Sumburgh Head. (Left click on pictures to enlarge).
The ACH unit at Noss Hill consisted of a domestic site, two
90ft wooden towers for the Transmitter and Receiver aerials and 3 huts,
surrounded by blast walls. The huts were for the diesel generators, transmitter
and for the combined receiver/ops room.
In
greater detail the ACH Ops/Tech Site looked like this:
The next picture shows the ACH Tech/Ops area from the
north-west. The blast walls for the Receiver Hut can be seen in the distance,
the power would have been located in the compound centre left and the
transmitter hut centre right:
The next photo shows the blast walls which surrounded the
Receiver Hut, the footings for the 90ft aerial tower can be seen on the right.
The walls constructed to surround the Transmitter and
Receiver are of similar size. Very little, other than sheep droppings, is left
inside the blast walls as can be seen from
the following photo, taken where the Transmitter Hut used to stand.
The area which housed the diesel generator is a different
shape from the compounds which housed the "T" & "R"
Huts, it also has a much larger concrete foundation inside. There are a couple
of apertures, which can be seen in the far wall in the next picture - these
were possibly used to convey the exhaust fumes from the diesel engines out of
the confined space.
Whilst the footings for the "T" &
"R" aerial towers were of concrete and steel, the towers themselves
were 90ft tall and made of wood. The legs formed a 10ft square at the base and
each leg was 5" x 5".
The
larger Final Chain Home site took much longer to build and was massive in
comparison to the initial ACH unit. The aerial towers dwarfed their earlier
cousins and the Transmitter and Receiver/Ops blocks were larger and contained
in hardened bunkers. A hardened Standby
Set House, with back-up diesel generators, was also constructed. The labelled
extract from Flash Earth shows the main Op/Tech buildings on the CH Site -
better descriptions and illustrations will follow.
One of the structures marked on the plan above would not
have been there when the CH site took over operations from the ACH site, that
containing the IFF equipment - more on this later. I do not have a completion
date on the VEB so that may also have been constructed after the rest, once
again more later.
CH Transmission
Firstly, I'll take a look at the transmission side of the Noss Hill CH
station. Unfortunately, the bunker which used to house the transmitter
equipment is sealed and entry is not possible. However, some details are
evident. It's exterior dimensions and shape are the same as the similar
building at RAF Skaw - the block measures 72' x 26'. The first two pictures
show the outside of the Transmitter Block.
There are some small holes in the wall which appear to reveal the Transmitter Room at the western
end of the block and a very small broken window at the eastern end of the block
which reveals a large chamber, part of
which can be seen below:
The radar construction programme in UK was an immense
undertaking and, to help speed-up progress, standard plans were drawn up for
each type of installation. These plans were adapted to a certain extent on site
dependent upon variations in available material and local features. For CH
radars there were two main types of plans, those
for the earlier east coast stations and those for the later west coast units.
The differences were significant with regard to equipment, towers and buildings
but rather complex for explanation here. RAF Noss Hill and RAF Skaw surprised
me in having features associated with both east and west coast CH Sites. At both sites the layout of the Transmitter Blocks
follow the plans for a standard east coast CH site, though with the inaccessibility of the Noss Hill structure. it's difficult to discover what equipment was inside.
The two Transmitter towers were massive steel structures ABOUT 360
ft tall and could be seen from long distances. At ground level the 4 legs of
each tower formed a 64 ft square. The
following picture, taken just after the war and held by the Shetland Museum
& Archive Photo Library, shows the site from the north with the Loch of
Spiggie in the foreground - the Transmitter towers are the 2 tallest on the
left.
CH stations operated on two wave-bands - 10.10 to 13.27
metres and 5.9 to 7.1 metres. Most CH Stations used wavelengths in the longer
band. For comparison, the Type 80 search radar, which was introduced in the mid
50's and installed at Saxa Vord, had a wavelength of about 10 centimetres and the Lightning fighter airborne
intercept radar - the AI23B - had a wavelength of about 3 centimetres.
Note:
During my visits to the Noss Hill CH site the Transmitter
Block was sealed. I recently heard from Sammy Sjoberg who has been able to gain
access to the building. He sent me photos of the inside and has kindly allowed
me to attach some of them to this article.
Considering its age the structure the interior seems to be in excellent
condition. I have added a sketch of the RAF Skaw Transmitter Block. which was
similar, to provide an idea of the layout:
