The Cobra Mist project at Orford Ness was conceived as a high-power Anglo-American over-the-horizon radar program, but its public legacy became the unresolved clutter-noise anomaly documented in declassified technical files.1
Origin
The project emerged from early U.S. over-the-horizon experiments and was moved from an initial Turkish option to Orfordness after Turkey declined hosting, when British planners offered a site on the Suffolk coast.12
By 1966 the Air Force had selected RCA to build the AN/FPS-95 system, classified as a Secret joint Anglo-American operation, with construction beginning in 1967 and operational planning continuing through 1971.1
Who reported or observed it
Anomalous performance was first documented in the on-site joint program by the Design Verification System Testing (DVST) teams, who reported in late 1972 that a severe “clutter-related noise” occupied range bins where target returns were expected.13
The anomaly was also seen by the DVST Technical Committee, which then triggered transfer of program control to a civilian scientific director and formation of the US/UK Scientific Advisory Committee (SAC) in January 1973.1
Narrative evolution
In December 1972 HQ USAF directed that testing mode change from normal DVST/IOT&E to an investigation of the noise problem because internal hardware remediation had failed to restore required performance.1
The SAC ran targeted experiments through May 1973 and reported that source elimination remained incomplete, even after expanded hardware checks and environmental testing, though several specific improvements were identified.143
On 1 May 1973, findings were briefed to US and UK defense leadership; on 29 June 1973 the U.S. and MOD public position announced project termination, and operations were phased out by 30 June 1973.15
After deactivation, the radar was dismantled and no operational reuse occurred at that site for surveillance, while the infrastructure shifted to civilian transmission ownership in later decades.2