It's been revealed that US and Soviet nuclear submarines crashed off the coast of Britain in 1974, in an incident one expert has claimed could have led to a third world war.
The collision involving American sub USS James Madison (pictured above), which was carrying 160 nuclear weapons, was detailed in a newly-released official CIA document.
The incident took place about 30 miles from Glasgow in shallow waters near Holy Loch, Argyll, at the height of the Cold War.
It was then covered up for over 40 years.
The US had a nuclear submarine base at Holy Loch between 1961 and 1992. The document read:
"Have just received word from the Pentagon that one of our Poseidon submarines has just collided with a Soviet submarine."
"The SSBN James Madison was departing Holy Loch to take up station when it collided with a Soviet submarine waiting outside the port to take up trail.
"Both submarines surfaced and the Soviet boat subsequently submerged again. There is no report yet of the extent of damage. Will keep you posted."
The cable was marked "Secret eyes only" and sent to Henry Kissinger, then the US Secretary of State, by a national security adviser to President Ford.
It was among around 13 million pages of unclassified documents that have been published online this month by the CIA.
Last week the files revealed that the CIA planned to give the Falklands to Argentina if the country won the war against Britain over the islands.
It is understood that James Madison was left with significant damage to its hull after the 1974 incident and was taken into dry dock for inspection and repairs.
Hans Kristensen, a nuclear weapons expert, said:
"If the crew on one of the submarines had misinterpreted the collision as an attack and decided to defend itself and sink the other submarine [there could have been a disaster]."
"The submarines could also have capsized with loss of all on board, leaving ‘hot’ nuclear reactors in relatively shallow waters close to rich fishing grounds."
Another expert, meanwhile, warned that the quite "considerable amount of plutonium" that could have been released into the marine environment "would have caused serious contamination."
It comes after reports that a missile malfunctioned during a recent test of the Trident nuclear deterrent.
The SNP have now said that the 1974 incident highlights the danger of housing nuclear submarines in British waters.
SNP defence spokesman Brendan O'Hara said the collision is "deeply worrying" and clearly a "lucky escape", and compared the secrecy over it to that of the Trident test:
''The truth is - as we saw with the Trident malfunction revelations - nothing has changed, it could happen again."
''We keep asking the UK government to realise how dangerous - how unsafe - how unreliable these weapons of mass destruction are."