A ROYAL Navy nuclear sub sinking towards its crush depth was saved moments from disaster.
A depth gauge failed on the decades-old Vanguard class vessel, carrying 140 crew and Trident 2 doomsday missiles in the Atlantic.
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Such a catastrophe would also have triggered a nightmare salvage mission to recover the top-secret vessel and its nuclear reactor before the Russians got to the scene.
The sub was preparing to go on patrol when dials indicating its depth stopped working, leaving commanders to think it was level when it was still diving.
It was entering the “danger zone” when engineers at the back of the 490ft Vanguard-class vessel spotted a second gauge and raised the alarm.
A source told The Sun: “It’s not the engineers’ job to control the sub’s depth but they saw how deep they were and realised something was wrong.
“Technically the sub was still at a depth where we know it can operate, but if it ever has to go that deep the whole crew is piped to action-stations.
“That hadn’t happened. The sub wasn’t supposed to be there, and it was still diving. And if it had carried on going, it doesn’t really bear thinking about.”
The Sun is not naming the sub or the depths involved for security reasons.
A naval source said the near-miss had showed that safety systems worked.
They added: “If one system fails you can fall back on the other.”
Top Brass launched an urgent safety probe but insiders insisted the drama did not interrupt the UK’s nuclear deterrent.
At least one Royal Navy submarine with nuclear missiles has been on patrol continuously since 1969 to hit back in the event of a doomsday attack.
Britain has four Vanguard-class submarines but currently only two are operational.
One is having a major refit and the other is undergoing sea trials after repairs that ran £300million over budget.
The Navy said: “We do not comment on operations. Our submarines continue to be deployed globally, protecting national interests.”
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