PM makes rare visit to nuclear-armed submarine to show UK's strength - but Putin will notice a potential weakness

Sir Keir Starmer has boarded a nuclear-armed submarine as it returned from a lengthy patrol - in a rare showcasing of the UK's nuclear deterrent that will catch Russia's attention at a time of growing tensions.

While being reminded about British nuclear strength though, Russian President Vladimir Putin will also doubtless take note of a potential weakness.

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 - as issues with maintaining the ageing fleet make it harder to rotate the boats more quickly.

The Royal Navy must keep one nuclear-armed submarine at sea at all times.

The so-called "continuous at-sea deterrence" is the cornerstone of UK defence strategy and the ultimate guarantor of the nation's security.

It is the first time a prime minister has visited one of the Royal Navy's four top-secret nuclear-armed submarines as it returned from a deterrent patrol - a moment known as "Day Zero" - in more than a decade.

The last time this happened was with David Cameron in 2013.

The trip was revealed as senior military officers from a so-called "coalition of the willing" to help Ukraine in any ceasefire deal with Russia were due to meet at a UK military headquarters on the outskirts of London to discuss plans for an international force to be sent to the country.

The prime minister will attend part of the meeting.

Video released by the Ministry of Defence (MoD) showed Sir Keir, eyes pressed to pair of binoculars, and Defence Secretary John Healey sailing out to greet the ageing submarine - which had surfaced - as it re-entered UK waters off Scotland earlier in the week following what was reported to have been a 204-day patrol.

The MoD declined to confirm the length of time the boat had been at sea. The longest known deployment - of 207 days - was carried out in 2021 by HMS Victorious.

Patrols by one of the UK's nuclear-armed submarines - which used to last three months - have had to be extended in recent years because of prolonged periods of maintenance and repair work on the other boats.

The fleet is operating well beyond its original in-service life of 25 years because of delays in the building of four replacement boats.

In a show of support for what is known as the "silent service", the prime minister, dressed in a Royal Navy-style coat, could be seen in the footage stepping onto the topside of HMS Vanguard as it bobbed in the water.

He was joined by Mr Healey as a line of submariners stood to attention, before they both clambered down a hatch into the vessel.

The two men, followed by Admiral Sir Ben Key, the head of the Royal Navy, walked around inside the submarine and received what was described as a "hot" brief on the deployment.

The official release of any information about the UK's nuclear deterrent is extremely rare.

Filming of any of the boats is also highly unusual and strictly controlled.

Britain's enemies will likely be scouring the images that were made public for any clues that might reveal any information about the military's most potent weapon and the ultimate guarantor of UK security. All audio was removed before release for security reasons.

The decision to publish details and images about the visit appears designed to send a signal to Moscow that the UK remains a nuclear-armed power.

It came as the prime minister and defence secretary prepared to visit a sprawling BAE Systems manufacturing site in Barrow, a port town in Cumbria, where the new generation of nuclear-armed submarines is finally being built to replace the Vanguard-class vessels.

The whole programme to renew the UK's nuclear deterrent - the submarines, missiles and warheads - is expected to cost more than £30bn, with an additional contingency of £10bn - making it the UK's most expensive and important procurement programme.

Sir Keir described Barrow as a "blueprint" for how defence spending can bolster security and boost economic growth by generating highly skilled jobs and opportunities.

"This week, I saw first-hand the sacrifice our submariners are making every day to keep our country safe, but I know they are only able to do that because of the support of the town of Barrow," he said, in remarks released in advance by the government.

"Each and every person living and working in Barrow is contributing to our nation's defence, whether that is building our world-class submarine programme, or supporting the workforce here through vital public services or proud family businesses."

In a sign of the importance of the programme, the prime minister will lay the keel, a longstanding maritime tradition that marks the official start of construction, to the first Dreadnought-class boat on Thursday afternoon.

In addition, the King has agreed to give the "Royal" title to the Port of Barrow "in recognition of the town's unique and critical contribution to national security", the government said.

The Royal Navy has maintained one of four submarines loaded with nuclear-armed missiles permanently at sea since the first patrol was launched in 1969.

But the age of the current fleet and increased requirement for repair work raise the risk of failure. Any break in the continuous at sea deterrence would be a devastating blow, undermining the UK's ability to deter the most existential of threats.

As well as visiting HMS Vanguard earlier in the week, the prime minister and defence secretary also spoke with family members of the submariners who have been at sea for more than half a year. Four crew members returned to meet newborn babies.

(c) Sky News 2025: PM makes rare visit to nuclear-armed submarine to show UK's strength - but Putin will notice a potential weakness