During the Cold War the American armed forces operated a variety of system to enable them to monitor Russian and possibly Chinese missile tests - collectively these systems operated under the Cobra nickname. On Shemya Island, at the end of the Aleutian Islands just south of the Arctic Circle off Alaska, a huge phased array radar, known as Cobra Dane, was sighted to allow the monitoring of Russian missiles warheads as they re-entered the atmosphere. A ship, the Observation Island, was also stationed near the Kamchatka Peninsular to monitor missile tests and was known as Cobra Judy. Two specially modified RC-135 aircraft, known as Cobra Ball, equipped with long range photographic and telemetry equipment flew out of Shemya Island to also monitor the missile tests.
However, the strangest item of equipment in the Cobra series was the Cobra Mist Over The Horizon (OTH) backscatter radar set up at Orford Ness in Suffolk during the early 1970's. The radar, known officially as an AN/FPS-95 OTH, was usually referred to as System 441A, and consisted of a massive fan shaped array of aerials occuping a 119 degree sector of a circle, 2200 feet long, supported on masts from 42 to 195 feet high arranged 8 degrees 40 minutes apart. At the time of its installation, Cobra Mist was the largest, most powerful and most sophisticated OTH radar of its time. The radar was controlled from a large steel blockhouse which stood on short legs behind the array and was connected to the array by cables running to an underground chamber, lined with copper, in front of the array. The system was scheduled to be operational by 1 Jul 72, but due to delays this was delayed until 1 Jan 73. However, in the combined Design Verification System Test (DSVT) and Initial Operational Test and Evaluation (IOT and E) during the summer and autumn of 1972, severe background noise was encountered which greatly reduced the detection capability. Despite considerable efforts to establish the source of the noise and eliminate it, the background noise continued to severely affect the radars performance and eventually it was decided that the economics of attempting to overcome the problem simply couldn't be justified, the entire project was cancelled and the radar dismantled and removed.
For many years the exact purpose of the Cobra Mist OTH radar was shrouded in mystery. This in turn led to the usual spate of 'X-file' stories which linked the radar to various UFO sightings. Now with the release of various documents in the USA under the FOIA, its possible to determine that Cobra Mist was designed to 'overlook air and missile activity in Eastern Europe and the western areas of Russia' in an arch from 19.5 to 110.5 degrees clockwise from true north. Tests in the USA had shown that a similar system could detect aircraft targets at ranges between 1500 and 2000 miles and the original plan was to site the system in Turkey, but when Turkey refused to make a site available, the search moved elsewhere and eventually settled on Orford Ness. When operational, it was planned that Cobra Mist would be manned by a mixture of USAF and RAF personnel. It's possible that the radar failed to work correctly because it was jammed, possibly by a Russian trawler sitting somewhere out in the North Sea, which also leads to the conclusion that it was compromised by Soviet agents whilst it was under construction. The failed system eventually ended up costing the US anywhere between $100 - $150 million.