Site Records


Site Name: RAF Sopley ('AVO') R3 GCI ROTOR Station


Sopley
Hampshire
OS Grid Ref: SZ162978

RSG site visit 23rd May 2000

[Source: Nick Catford]

Following the end of the war the air defence system was reviewed in the light of experience and a now much reduced budget. One outcome of this was to nominate one GCI station in each sector to be an SOC/GCI (Sector Operations Centre) which was in effect the reserve SOC should the main SOC become non-operational. This upgrading involved the construction of an extension to the operations room to accommodate four new cabins with two windows overlooking the reporting hall, whist the intercept cabins behind the chief controller were rearranged and enlarged, the RT monitors being relocated in the admin section. These SOC's remained in use until superceded by the R3's, R6's and R8's of the rotor system. Sopley became the SOC/GCI for the Middle Wallop Sector.

Sopley continued to operate as a GCI station, becoming the Sector Operations Centre for Southern England in 1950. By 1950, the threat of the atomic bomb had caused a serious rethink in the organisation of air defence and a plan, codenamed ROTOR, was instituted to replace many of the existing stations with new protected underground operations rooms. For GCI Stations these were designated R3 (west coast GCI stations which did not require the same level of protection were located in R6 surface blocks)

Cutaway drawing on an R3 underground GCI technical building
Drawn by Jason Blackiston

The R3 was never intended to survive a direct hit from a nuclear weapon but was designed to withstand a near miss from Russian pattern bombing with 2,200lb armour piercing high explosive bombs (BRAB) dropped from 35,000 feet. It was decided to rebuild the GCI station at Sopley on the opposite side of the road to the happidrome in the field originally occupied by the mobile installation in 1940.

The new station became operational in the summer of 1954 using the callsign 'AVO'; it was fitted with the following radars: one Type 7 Mk. II, one Type 11 (Mobile) Mk. VII, two Type 13 Mk. VI, two Type 13 Mk. VII, one Type 14 Mk. 8 and one Type 14 Mk. 9. A new domestic camp for 450 personnel was built near Bransgore village but until this was complete accommodation was provided until 1952 at RAF Ibsley which had closed as an active base in 1946.

Photo:The guardhouse gives access to the two level R3 bunker below
Photo by Nick Catford

During 1956 Decca Type 80 Mk. III search radar was installed, replacing the earlier Type 7. The Type 80 was developed in the early 1950's from an experimental design based on the Type 14 Mk VI under the project code name Green Garlic. At this time the two Type 14 radars were dismantled and removed

Almost overnight this new radar made parts of the ROTOR air defence system redundant. The Type 80 improved the range of the station considerably with a range of up to 320 miles compared to the 90 mile range of the Type 7; this instantly made some of the earlier equipment obsolete.

Photo:Sopley Type 80 radar and modulator building

Inside the R3, dramatic changes were also taking place. The large two storey operations room was superseded by a much smaller control room constructed on the top floor at the opposite end of the building. This included a 'well' in the floor for a photographic display unit (PDU) which allowed radar pictures to be projected up into a plotting table from the room below housing a Kelvin Hughes Photographic Projector.

This consisted of equipment that could record the radar image on 35 mm film, develop, fix and dry the image and then project it up on to the plotting table in the control room on the floor above. The displayed image was one minute behind real time. The PPI image from a high intensity cathode ray tube was projected on to the film through a focusing lens. Each revolution of the radar antenna took 15 seconds and it took this time to expose the film to a full revolution.

At the end of the sweep, the frame would be moved on to be developed, whilst the next frame was exposed. When the frame moved on at the end of the next sweep the image was fixed, it then moved on again to be dried. Finally the frame moved on once more where it was projected, via a mirror, to the underside of the frosted glass plotting table on the floor above.

Meanwhile the next frame to be exposed has been following on through the process, so at the end of the next revolution this frame was projected, 15 seconds after its predecessor.

Finally the frame moved on once more where it was projected, via a mirror, to the underside of the frosted glass plotting table on the floor above. Meanwhile the next frame to be exposed has been following on through the process, so at the end of the next revolution this frame was projected, 15 seconds after its predecessor. As frame after frame was displayed on the map the plotters in the pit could place markers on the map to indicate friendly or hostile aircraft.

Room layout at Sopley following the installation of the Kelvin Hughes PDU
Drawn by Nick Catford

With the installation of the Type 80, the Station continued to operate in the Air Defence Role as a Fighter Control Unit manned by members of the Royal Auxiliary Air Force and while many stations closed Sopley was required for the 1958 Plan.

Click here to continue the history of RAF Sopley

[Source: Nick Catford]

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