Site Records

Site Name: RAF Ventnor ('OJC') R1 CEW ROTOR Radar Station

St. Boniface Down
Ventnor
Isle of Wight
OS Grid Ref: SZ568785

Sub Brit site visit 1st October 2004

The RAF finally left the site in 1961 and the station was taken over by the Ministry of Aviation for use as a radar and communications station for the Civil Aviation Authority.

It was also used as a test location for more exotic systems, and unusual antennae occasionally came and went. A satellite dish, approximately 4 to 5m diameter, was temporarily installed nearby in the mid 1970's. Missile tracking, the explanation advanced locally, was dismissed by former workers at the nearby Needles civilian rocket launch site, several of whose firings had resulted in unplanned splashdowns and for whom tracking was something of a painful subject.

The CAA did not require the R1 bunker and in 1962 this was gutted and refurbished as the Isle of Wight County Control Centre from where the Island would have been administered in the event of a nuclear attack. This remained operational until the end of the cold war as the Isle of Wight Emergency Centre, finally closing in 1991.

The bunker was handed back to the CAA who decided they had no further use for it. The bungalow/guardhouse, air vents and the emergency stair tower were all demolished and the shafts capped with concrete with a hatch for emergency access. After several attempts to break into the bunker the concrete cap was covered over in 2004 and the site of the guardhouse was landscaped leaving no evidence of the entrance to the R1 which still remains below ground in pristine condition.

The chain home towers survived until 1957, the CH transmitter block which was within the rotor compound survived until at least 1998 but when the site was surveyed in 2004 it had been demolished. The Type 80 modulator building and adjacent redundant CAA Secondary Surveillance Radar (late pattern IFF) circular buildings still survived in 2004; these worked in conjunction with two CAA Type 264 radars which have been removed together with their gantries and buildings. The two SSR's are due for demolition in the near future as they have proved a target for vandals and as a result the entrance doorways have all been bricked up.

The chain home receiver building stands just outside the ROTOR compound; this is currently owned by BT but was offered for sale in late 2004 so its future is uncertain.

The following is an edited description of RAF Ventnor by Don Adams who served on the station from 1955 - 1957. For a more detailed report on Don's time at RAF Ventnor see his excellent RAF Ventnor web site.

The Chain Home masts, still in place in 1955

"A large enclosed area at the top of St.Boniface, 750 feet above the sea, contained low buildings and the tall old CH towers. I could see three Type 13's nodding away benignly and a Type 14 on top of a low tower, but the whole scene was dominated by the Type 80 steadily rotating at 4 revolutions per minute. I accompanied the Warrant Officer into 'the bungalow' and into his office where he issued me with a fitter's tool box, the contents of which had to be checked and signed for. .

The small gray bungalow built just inside the chain-link perimeter fence somewhat optimistically disguised the entrance to the bunker. Besides providing access to the top of a circular stairway guarded by a Service Policeman, the bungalow accommodated the Technical Officer together with his Warrant Officer. The roof space was used to store a small quantity of spare units for the radar 'heads'

The tunnel, which was about eight feet square, descended at a significant angle and was brightly lit, had smartly painted rendered walls and had a highly polished brown linoleum floor. After about 30 yards there was a wall mounted glass fronted cabinet which contained two service revolvers. It was hard to imagine the purpose of these, especially when I later learnt that the bullets for these were kept in a safe in the office above. The corridor continued, then turned sharply left and after another thirty or so yards reached a pair of massive blast doors. These were well over a foot thick and presumably motor driven, but thankfully I never saw them closed. The corridor was now at the right-hand side of a large room known as the Radar Office.

After this, doors on the right gave access to Officers' and Other Ranks' refreshment rooms and on the left, curtained access to the Operations Room. Next, also on the left, double doors led to a few steps down into a large high ceilinged 'plant' room housing ranks of motor generating equipment and air-conditioning apparatus. The corridor, now being only six feet across, continued through double doors and around a corner to a bolted heavy steel door through which was the main ventilation shaft which doubled as a route to the emergency exit. The shaft contained a zigzag of several flights of steel stairs and a large waterfall air washing system. Finally a heavy door in the side of the shaft, now a steel tube, opened to fresh air.

The name 'Radar Office' was somewhat a misnomer, the only desk being a small one for the shift diary, although there was a partitioned office in one corner. The whole room was filled with rows of rack-mounted electronics. The valve technology of that time was bulky and generated vast quantities of waste heat, so each rack was fitted with forced air cooling, and thus the noise level within the room was irritatingly high. Some of this equipment was my concern, but most was not. Each of the radar transmitters required a clock pulse to initiate each modulator pulse and these had to be in synchronism otherwise one radar in receive mode might be force fed with the pulse being transmitted from its closely adjacent neighbour, with dire result. So all clocks were derived from one master and that was generated from a crystal oscillator at a high frequency and repeatedly divided down to the 270 rate required and this equipment was deemed to be the province of the above-ground engineering staff, and was contained in but one rack amongst the serried ranks of the many others in the Radar Office.

I later learnt of the contents of some of these cabinets. For example Range Rings and Video Map, which rightly belonged to the 'Consoles', trained fitters and mechanics, hence I know little of the details of these, but a few words are appropriate. Range rings were concentric bright rings which, at the flick of a switch, could be made to appear on the displays at the same time as the targets. They were at set distances apart, say 50 miles, and thus the operator had an easy way of assessing the range of a target. The pulses to create the rings were generated entirely electronically.

Video Map required a little more ingenuity. Here, also switched on as desired, an outline map of the entire coastline in range, together with a grid map, was superimposed on the surface of the screen whilst still allowing the targets to be seen. The source of the map image was an acetate sheet on which all the details were drawn. Over this was mounted a lens which concentrated the image onto the aperture of a photo-electric cell. Under the acetate sheet was the face of a six inch white phosphor cathode ray tube (CRT). This did not display the radar echoes but just a bright radial line which rotated in synchronism with all the proper displays. Thus the map was scanned and the PE cell produced an output which could be distributed to the consoles as a video input.

The beauty of this system was that the timebase (operator selectable) at different consoles could be set to different ranges but the map always expanded or contracted in proportion, as did the range rings. The Video Map required careful setting up but was extremely effective, and there were two of these units in the Radar Office.

Another remarkable apparatus was the Monitoring system. This aid to fault-finding was a large-screen oscilloscope which was built into the racks at a central point and the screen could be slewed to facilitate easy viewing. It was fitted with two large rotary multiposition (perhaps 20) switches. Combined use of these allowed hundreds of crucial waveforms from countless sources within the Radar Office to be displayed. Reference to a bulky volume revealed whether or not each was correctly formed.

A curtained archway in the side of the Radar Office gave access to the Operations Room. Darkness ruled here, the only normal illumination coming from the amber and green glows of the CRT displays and that from the circular dynamic Plotting Table. At about ten feet in diameter this was in fact not a mere table, but a display of an image from a projection system which the officer in charge viewed from a tall 'umpire's' chair. The targets were thus magnified to about an inch across and they seemed to swim about on a somewhat watery surface, but the broad gently illuminated area was more restful to the eye than a CRT and allowed the overall situation to be viewed for extended periods.

Arranged around the room there were sets of the normal consoles, each pair consisting of an amber fifteen inch Plan Position Indicator (PPI) driven from the Type 80 or Type 34 search radars together with a nodding height finding display from a Type 13. The origin of the trace of a PPI display was normally the centre of the CRT, but operator controls could move this to any point of the surface. If moved say to the southwest periphery then only the northeast 90 degree sector was viewable thus concentrating the operator's interest in that area but allowing a much greater range to be monitored. The Type 34 was in fact a Type 14, but received this new title when mounted on a 25 foot high wooden gantry. This arrangement gave very good low level cover to and beyond a more distant horizon. Thus at Ventnor, shipping was effectively monitored together with low flying aircraft, the two being differentiated by the size of echo and speed of progress. Casual chatter was banned in this room; the only voices heard were those of the operators' quietly relaying information via telephone headset to a distant central Control establishment or directly to an aircraft by means of VHF radio.

Stairs in one corner of the room led down to a cellar containing the Kelvin Hughes Photographic Display Units and an associated Darkroom. The PDU provided the image for the Plotting Table. A small very bright radar display with a whitish phosphor was photographed onto Ilford HP3 35mm film once per revolution of the trace. The exposed frame moved on into a chamber where it was sprayed with developer. After a brief interval it was sprayed with water and then with fixer. A final water spraying took place and then it was blown with hot air. Each stage took fifteen seconds and a minute after the initial exposure the frame was in the projection station. The image was directed by mirrors to the undersurface of the Plotting Table in the room above.

There were two PDUs, left-hand and right-hand, both projecting towards the final mirror mounted between them. By manually flipping this over, the image from either PDU could be directed upwards. The film in the PDU was a 50 foot reel loaded in a cassette by the fitter or mechanic in the darkroom. When the film was close to the end, a buzzer in the Radar Office called for attention, as did low levels of developer or fixer. The drill was to then switch on the resting PDU and after a minute flip over the double-sided final mirror to allow the newly activated machine to provide the image. The first machine could then be serviced without haste. An additional facility provided by the PDU system was that the used film could be archived and used for post-mortem purposes after any event such as mid-air near collisions. The disadvantage of the system was that the overall picture on the plotting table was a minute late, but the viewing officer always moved to a normal console at a time of particular interest or impending crisis.

Further information and pictures of RAF Ventnor click here

Home Page

© 2004 Subterranea Britannica