By the late 1950s both Russia and the West had built a huge arsenal of nuclear weapons, at great cost, and tentative steps were being made to find some common ground.
But then a theory would send scientists and politicians into a dangerous tailspin which, amid greater fear and mistrust, could have led to catastrophic nuclear conflict. Amid the utmost secrecy, that global conflict suddenly came very close to home – to a hill which provides panoramic views across Plymouth to the Eddystone lighthouse.
The wild and rugged landscape of Kit Hill – some 1,000ft above sea level – and 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.
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
‘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 that 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 this 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. 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. Seventy five 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, a successful lead mine in the Lake District, 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 Western Morning News even employed a qualified mining engineer to survey the tunnel with a Geiger counter to test for radiation. Nothing untoward was found.