Cobra Mist

Cobra Mist was based on the Naval Research Laboratory's experimental Magnetic-Drum Radar Equipment ('MADRE'), which was able to reliably detect aircraft at ranges up to 2,000 nautical miles (3,700 km) from its base in Chesapeake Bay. With prior setup, MADRE was even able to detect rocket launches at Cape Canaveral and atomic tests in Nevada.[2][lower-alpha 2]

With this successful demonstration, the US Air Force started plans to deploy a similar system in Turkey; providing coverage of much of the western part of the Soviet Union. Tenders for the system outline were placed in 1964 and bids followed the next year for the actual system itself. However, Turkey refused to provide a base for the system and a search started for a new location.[3]

After some time the British offered a site in Suffolk. From this location the radar would be able to see almost all of Eastern Europe as well as the western parts of the Soviet Union. In particular, it would be able to track missile launches from the Northern Fleet Missile Test Center at Plesetsk. Although not as useful as the original site in Turkey, the UK site was nevertheless acceptable and the USAF accepted the new location.[2]

In 1966, a new series of bids were sent out for a system to be installed at this site, which was won late in the year by RCA. Construction of the site started in mid-1967 with the buildings and support systems which had to be carefully shielded to avoid contamination from signals being reflected locally. Many of the buildings had to be built on short stilts because the site was below the maximum water height recorded some years earlier.[4]

The site was completed on 10 July 1971 and testing began a week later. Tests of the broadcast system were extensive, including both local measurements as well as tests from distant aircraft. These were completed by September and attention moved to the reception systems. Minor storm damage in October slowed this phase somewhat, but RCA turned the system over to the USAF in February 1972. The original plan to go operational in July was delayed until January 1973, in spite of a truncated testing period that combined the "Design Verification System Test" and "Initial Operational Test and Evaluation" periods.[4]

Through the early part of 1972 testing found a considerable amount of unexpected noise, which appeared as frequency shifting of the signal. This made targets appear in all of the filters (high-speed, low-speed, etc.) even when it seemed there was nothing of the sort in that area. For instance, the system would often report missiles being launched no matter where the radar was looking. A lengthy series of investigations into the source of the noise followed and, in desperation, the USAF eventually turned over the testing to a panel headed by SRI International. The new team continued testing from January to May 1973, but no convincing explanation was ever found. Internal problems with the equipment were eliminated as a potential source. One particularly interesting finding was that the distortion only occurred over land. Deliberate electronic countermeasures were not ruled out.[4]

Although the noise was never identified, the panel concluded that the system could still be made operational by further improvements in the receivers; although the resulting system would only be marginally useful. Instead the USAF simply gave up and on 30 June 1973 the system was shut down, never having been used operationally. It is estimated to have cost between $100 and $150 million (equivalent to $864 million in 2019).[4]

As part of the ABM Treaty, large long-range radars were limited to operation in the home countries of the operators. Whether this had an effect on Cobra Mist is unknown.[5]