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Cold War secrets beneath a Cornish hill

By This is Cornwall  |  Posted: January 20, 2009

  • Dawn light rises over the iconic Kit Hill mine stack

  • The 2,180ft Excelsior Tunnel in Kit Hill was used for mining operations between the 1870s and 1930s and reopened for test blasts in the 1950s and 1960s

  • The fenced-off entrance to the Excelsior Tunnel on Kit Hill as it was in the 1980s

  • Top Secret Ministry of Defence plans and documents relating to the Excelsior Tunnel on Kit Hill in East Cornwall, which was used as a location for covert Cold War operations in the 1950s and 1960s

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THE wild and rugged landscape of Kit Hill, a dominant feature of the South East Cornwall skyline, is now protected as an area of outstanding natural beauty.

Some 1,000ft above sea level, the hill – gifted to the people of Cornwall in 1985 to celebrate the birth of Prince William – provides panoramic views to the Eddystone lighthouse and the North Cornwall coast.

But its fine views, flora and fauna belie its long industrial history. There are also no clues to the crucial tests which took place deep below the surface which, it was hoped, would build trust between the West and Russia and pave the way to ending the nuclear arms race.

By the late 1950s both Russia and the West had built a huge arsenal of nuclear weapons, at great cost. Tentative steps were being made to find some common ground, particularly on a test ban treaty.

As Samuel Murphy explained in his book, Grey Gold: "An essential pre-requisite of such a treaty was an ability to make sure that none of the signatories could cheat by carrying out secret tests undetected, and it was arguments about the effectiveness of the systems for detecting surreptitious nuclear tests – whether they were in the air, on land, in the sea or underground – which deadlocked the talks.

"Then out of the blue came a potentially devastating bombshell in the form of a new scientific theory. An American scientist, Dr A L Latter, propounded the theory that it should be possible to camouflage the seismic signal from the detonation of an underground explosion so that it could either be missed altogether or made to appear many times smaller than it actually was.

"If this was true then the impending treaty was in jeopardy, for without mutual trust and without cast-iron guarantees that a transgressor could be detected, signing an agreement was just too dangerous for it could allow an unscrupulous state to obtain a decisive technological advantage over the others.

"No one had any idea as to whether this new theory, which became known as the Latter Decoupling Theory, would actually work as predicted, but it was essential that it should be tested before the treaty was concluded.

"On Government orders, scientists in the USA and in the UK set to work to devise experiments to check it out."

The fact was that an explosion underground could be detected by seismology equipment thousands of miles away and the size of the blast calculated. But the belief was that by detonating a small charge in a void the same size it would have created, the effects would be massively reduced.

Limited initial tests by the Atomic Weapons Research Establishment proved the theory and scientists' attention quickly turned to locations where larger tests could be carried out underground.

With their proliferation of redundant mines, Cornwall and Devon were obvious areas for study.

Secret files released from the National Archives show scientists had conducted "extensive geological investigations" on numerous mines across the region.

"They were therefore very familiar with these mines and had many of the facilities on tap for reworking them," the document states.

"Several of the mines were thought to be capable, with little attention, of providing the cover required for the 'zero room' for a one ton charge. And some, after de-watering, would provide the greater cover for the larger charges."

In Devon, they looked at the Vitifer, Golden Dagger and Birch Tor mines, near Chagford. In Cornwall, they considered nine mines from Penzance to Callington.

The report goes on: "Provided the political and legal problems could be sorted out, and there seems no reason to suppose they could not, work towards the firing of one ton charges could commence without delay in any or all of the following three mines, listed in order of preference – Tolgarrick (near St Austell), Wheal Bray (on Bodmin Moor) and Wheal Speed (Near Penzance)."

Quite why the 2,180ft Excelsior Tunnel in Kit Hill – which was started in 1877 and continued at intervals until 1938 – was chosen is not clear, although the report details its dimensions in great depth.

According to cuttings from the Western Morning News from 1959 and 1960, 75 controlled explosions were carried out over a period of several months. They were fired in 6ft diameter voids at depths of 100 to 300 feet. No nuclear material was involved. That was largely the end of the matter in Cornwall and the project – known as Operation Orpheus – moved on to Cumbria.

At the Greenside Mine 3,000lb charges were detonated. Massive explosions were also set off in a salt mine in Louisiana as part of transatlantic tests. The results were regarded as a resounding success, with the detectable effects of some explosions being reduced by a factor of between 10 and 30. The problem of detecting and deciphering such tests remains.

The tests under Kit Hill passed without incident at the time and local people were either unaware or else unperturbed. That was until March 1985, when mischievous newspaper reports suggested that nuclear waste had been stored in spherical granite chambers in the Excelsior Tunnel.

Following up the story, the WMN even employed a qualified mining engineer to survey the tunnel with a Geiger counter to test for radiation. Nothing untoward was found.

Local men who had worked on the tests steadfastly denied the claims, as did the Ministry of Defence.

Photographer Colin Higgs went down the tunnel as part of the exposé. He described the visit as an "eerie" experience, while the spherical holes cut in drives off the adit were "strange".

"It was very, very weird down there," he said. "But there wasn't any evidence that nuclear material had been stored in there. I think you might say that a lot of journalistic licence was used."

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