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COBRA MIST


The Cobra Mist site is a huge area on the Northern end of Orford Ness. This was one part of a series of projects under the Cobra codename. They were all designed to watch Russian and possibly Chinese missile tests, and movements of aircraft in the target area. This was some hundreds even thousands of miles away, because the radar bounced its signals off the ionosphere and listened for the return pulse along the same path. Two huge radar set ups would face each other along the same great circle. On Shemya Island was a phased array radar called Cobra Dane. A ship, the Observation Island, stationed nearer Kamchatka, was code named Cobra Judy. Two RC135S planes were used to gather photographic and telemetry data and were codenamed Cobra Ball. The strangely shaped radar set up on Orford Ness was to become part of this series. Its short life would tend to indicate it was not very successful. System 441A comprised a huge fan shaped array of aerials, 2,040 feet long, supported on masts from 42 feet to 195 feet high arranged 8 degrees 40 minutes apart. A large steel blockhouse on short legs stands behind this array. It was connected to the aerials by cables which ran to an underground switch chamber, lined with copper, in front of the array. Information released under the American freedom of information act reveals the following. “System 441a, known as COBRA MIST, was initiated to aquire, install, and test the AN/FPS-95 OTH radar set in an operational overseas environment at Orfordness, England.....System turnover was scheduled for 1 July 1972. However, due to several test delays the turnover was scheduled for 1 January 1973. In the interim it was decided to combine the Design Verification System Test (DSVT) and Initial Operational Test and Evaluation (IOTandE) in order to expedite the test program. In the combined DVST and IOTand E during the summer and fall of 1972, a severe noise problem was encountered which resulted in a reduction in detection capability. The range related noise had a median value of -65 decibels; in addition, there were noise modulation sidebands 10 to 30 hertz from the carrier with a median value of -60 decibels.”
Much work was done to establish the source of this noise and to try and eliminate it, but in the end it was decided that the economics of the situation were unjustifiable and the project was terminated. At least that was the story! There are other versions and it may be that the true effectiveness of the setup was much greater. A lot of data is still classified on this matter. It should also be borne in mind that at the time this site was abandoned as Cobra Mist, there were missile treaties on the table. This would not be the first, or last, time that US technology was to be used as a bargaining point.
After a visit to the site, here are a few pictures to show what remains now. Almost nothing remains of the actual Cobra mist radar itself. When the US part of the operation was over, all the kit was stripped out. The later use of the site by the British Government has left barely a trace either. Then it was taken over for use as a BBC World Service transmitter site. It could be argued this was still a part of the Cold War, but it is still going strong on this site. It seems the propogation from here is superb for the target area of Europe. What remains is the huge steel framed block house, which housed the transmitters, receivers and operating parts of system 441. The lower floor was the transmitter area, the upper the receiver area. There are offices, and control rooms and workshops. Some rooms are difficult to fathom, others more obvious. There is evidence of special security arrangements to protect the intelligence gathered, such as isolated mains power circuits, doors with special locking arrangements and so on. This was a heavily staffed, highly secure operation. The design life of the project was ten years, and this was some thirty five years ago. The place is massively over engineered.

Here is an aerial view taken in 1972, when the site was complete and as built. The clean white colour of the aerial field is due to the vegetation being treated to kill it off. This situation lasted for many years. Heaven knows what they used!


This closer view of the switching chamber end of the array shows the point at which the six feeds to the antennae arrived at the switch chamber, and the 36 connections to the 18 arrays came out. At this end the height of the arrays was 42 feet. Between the switch chamber and the arrays there was a set of baluns to prevent surges. It is possible to see the arrays slung between the masts.


This view of the block house shows all the other buildings and so on in the compound behind the arrays. Between the block house and the coaxial feeds to the switch chamber is a set of harmonic filters at the back of the block house. These are lage cylibers and can be seen in this shot.


This is the entrance to the compound, from inside.


The plinth in the above picture was the power supply area, and contained generators, this area is now almost clear, as here.


The whole block house and its anciliary plinths is built on stilts, as the 1953 flood level is the height of these columns. The front of the main building shows many shielded vents, as does the rear. An indication of the high power and heat output of the contained equipment.






The lower floor contains many small rooms as well as the transmitter hall, a rather large area. The style of the place is typical industrial/military and like a bunker in that it has no windows. There are windows in some areas now but these are not original.


This is an empty corner of the transmitter hall, perhaps a tenth of the overall area, there was plenty of space but even then the equipment over filled it and some was in another room.


Upstairs the receiver hall is empty and more original in its finish. There were a few odd rooms built within this space, some still remain. They are faraday screened areas with special door seals of berylium copper strip presumably to protect something from all rf sources. No indication remains as to whether this was from Cobra Mist or UK government days.




This is the location of the internal equipment hoist between floors.


This is the main control room, and the raised area with glass windows at one end was where there was a row of teleprinters. The separation was due to the noise they produced. It is still possible to see marks on the floor where the equipment was removed, as is the case in a number of other rooms. Not much has been disturbed over the years!




Just to prove that when Subterranea Britannica goes visiting, we leave no stone un turned, this is under the control room floor! Some information has come to light from a former worker here that it was not unknown for some of the people here to take a nap under the floor. There was also some equipment found here when the building was vacated by the Cobra Mist operators.


Out the back of the block house, into the huge antenna array field at the rear, where all the access roads were made of wooden railway sleepers, thousands and thousands of them, the area where the harmonic filters once was can be seen here, along with the plinths once occupied by water cleaning and coolling plant.


This shows the rear of the block house, just as anonymous as the other side. One thing which is modern is the cell phone mast on the roof!


At the far end of the site is the underground switching chamber. Here the equipment was housed in a copper lined chamber below ground level. To point the radar at a new target different antenna strings were switched in or out from this point. There were 18 of them allowing a fair degree of accuracy.


The crescent of steel pipes out from the chamber above was where the feeds to the arrays came out. They then passd to the balun pit, now a water filled area, shown in this picture, above those fingers of concrete. The block house can be seen in the distance, giving an idea of the huge scale of this site. Under it all was the metal mesh ground plane.



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