A ROYAL Navy nuclear submarine was saved just moments before sinking.

With the depth gauge failing, the UK’s nuclear deterrent started sinking towards its crush depth, which would have led to chaos and an emergency mission to recover the sub and 140 members of crew.

The Sun reported the submarine was about to go on patrol when the dials stopped working, with the commander believing the ship was level when it was, in fact, sinking. Thankfully, engineers on the other side of the sub noticed the second dial and raised the alarm.

Speaking to The Sun, a source said: “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 sub or the depths involved have not been named for security reasons but an urgent safety probe has been launched.

One Royal Navy submarine has been patrolling the world's waters since 1969 in case of a doomsday attack.

The Navy said: “We do not comment on operations. Our submarines continue to be deployed globally, protecting national interests.”