What we know about Royal Navy sub malfunction as 140 crew almost crushed underwater

A rapidly sinking Royal Navy nuclear submarine with Trident nuclear missiles was reportedly saved moments from disaster after a group of engineers noticed a faulty reading on a depth-measuring device.

An investigation has been launched into the incident after engineers managed to stop the submarine and its nuclear arsenal plunging further and into the so-called “danger zone” where the vessel could have imploded.

Here’s everything we know so far:

What happened to the vessel?

A depth gauge, a device that monitors the water pressure and displays the depth of the vessel, malfunctioned on the Vanguard class submarine, which was carrying ­Trident Two doomsday ­missiles across the Atlantic.

The vessel was plunging towards its crush depth – the depth at which a submarine will implode due to water pressure.

The sub was on patrol when the gauge stopped working, with crew believing the vessel was keeping level when in fact it was plunging deeper into the ocean.

Engineers at the back of the the sub located a second gauge showing they were descending into the danger zone and sounded the alarm.

“It’s not the engineers’ job to control the sub’s depth but they saw how deep they were and realised something was wrong,” a source told The Sun.

“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.”

“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.”

How big was the submarine and what was on board?

Vanguard subs can carry up to 192 nuclear warheads but are currently permitted to hold a maximum of 48. The Royal Navy would not disclose the depth the sub reached, but the maximum depth for a vanguard vessel is around 500 metres.

Around 140 crew members are believed to have been on board.

The incident has prompted an immediate investigation, The Sun was told, but it did not affect the UK’s nuclear deterrent.

It is unknown which of the Navy’s four Vanguard Class missile submarines was involved in the near-miss. The force’s four vessels – HMS Vanguard, Vengeance, Victorious and Vigilant – are more than 149 metres in length and each displace 15,900 tonnes when submerged.

One is being refitted and another is undergoing sea trials after repairs that exceeded £300m over budget.

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