Three of UK's four nuclear submarines out at sea

​​​​​​​Three of the UK's four nuclear deterrent submarines are out at sea, it is understood.

It is not clear why, but at least one of the vessels will be armed with nuclear warheads and be on routine patrol.

An expert said one of the other Vanguard-class submarines would likely be working up to take over the patrol, while the third could be undergoing sea trials.

The Ministry of Defence declined to comment.

The unusual deployment of most of the UK's fleet suggests improved availability, which has been a problem for the Royal Navy's submarine service in recent years.

It will doubtless be noted by the UK's enemies and its NATO allies.

The continuous deployment of at least one Trident submarine is regarded as the UK's ultimate security guarantee - its continuous at-sea deterrence.

Having three such submarines at sea at the same time is not routine, however.

The Times, which was the first to report on the activity, spoke to a source who described it as "unusual", though they did not explain why.

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Any change in the rhythm of the UK's nuclear-armed vessels is potentially significant, given the devastating weapons they carry.

Such action could be used to send a signal to opponents.

HMS Victorious, the fourth of the ageing Trident submarines, is in Devonport naval base undergoing maintenance.

The sight of three nuclear submarines being seaworthy will be welcome news for submariners, who have been forced to endure gruellingly long deployments because of poor availability.

Last year HMS Vanguard was kept patrolling at sea for more than 200 days - one of the longest-ever deployments that will likely have put a huge strain on the submariners and the vessel.

The longest known deployment - of 207 days - was carried out in 2021 by HMS Victorious.

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