Russian sensors suspected of attempting to spy on the UK’s nuclear submarines have been found hidden in the seas around Britain.
The discovery by the British military was deemed a potential threat to national security and has never been made public. Several were found after they washed ashore, while others are understood to have been located by the Royal Navy.
The devices are believed to have been planted by Moscow to try and gather intelligence on Britain’s four Vanguard submarines, which carry nuclear missiles.
One of these submarines is always at sea under what is known as the UK’s continuous at-sea deterrent. The Sunday Times has chosen to withhold certain details, including the locations of the sensors.
During a three-month investigation we spoke to more than a dozen former defence ministers, senior armed forces personnel and military experts to expose how Russia is using its unrivalled underwater warfare capabilities to map, hack and potentially sabotage critical British infrastructure.
We were allowed unprecedented access to the RFA Proteus, the Royal Navy’s deep-sea surveillance vessel, to witness how it is leading efforts to counter threats in domestic waters.
The investigation also found:
Senior military figures liken the technological battle for supremacy below the waves to the space race between the United States and the Soviet Union during the Cold War.
Now Britain has “woken up” to the Russian threat, the question is whether it is capable of catching up.
First line of defence
At 8.45am on March 21, a black inflatable speedboat is skimming across Campbeltown Loch towards one of the most secretive vessels in the Royal Navy’s fleet.
The Sunday Times has joined senior naval officers being ferried to the RFA Proteus, named after the sea god in Greek mythology, as its crew spend the week training and experimenting with cutting-edge underwater vehicles.
Anchored just off Scotland’s westernmost town, the Proteus forms an imposing silhouette against the Isle of Arran, its giant helipad and deep-sea crane clearly visible from a mile away.
It is the first time a journalist has been allowed to observe its capabilities since the vessel came into service in 2023. On deck, helmeted crews prepare remotely operated vehicles that later today will be lowered to the sea bed via a moon pool — an opening in the hull the size of eight snooker tables. Other, more sensitive equipment is stowed in blue metal containers.
Already aboard are two dozen members of the navy’s diving and mine-hunting squadrons, experts in searching out, recovering and destroying enemy munitions on the sea bed.
They are here for the first time and will become an integral part of the ship’s operations, because Britain’s critical undersea infrastructure is under unprecedented threat from a long-standing nemesis: Russia.
Cat and mouse
When the Berlin Wall fell in 1989, the might of Russia’s non-nuclear forces went with it. But according to Royal Navy insiders, Moscow never stopped investing in the submarines patrolling the murky depths of the world’s oceans.
Russia is the only nation with a fleet of specialist subs for sea-bed warfare and espionage. Some surpass the capabilities of those of Britain and its Nato allies.
By the time President Putin sent tanks into Ukraine three years ago, Russia had already begun setting the stage for a much wider conflict with Nato, engaging in surveillance and sabotage of the underwater internet connections, energy pipelines and military cables that are vital to the functioning of western democracies. These activities are at the heart of Putin’s “greyzone” doctrine.
The blowing up of the Nord Stream gas pipeline in 2022 was the first major incident; Royal Navy insiders maintain that its “military precision” had all the hallmarks of a Kremlin greyzone operation.
In the past 15 months, at least 11 internet cables in the Baltic Sea have also been damaged, some from ships dragging anchor across the sea bed. Suspicion has come to rest on Russia’s shadow fleet of ageing tankers, which are mainly used by Putin to circumvent western oil sanctions. “You really need to keep the [engine] power on to drag, so it is a deliberate act,” a defence insider said. When a cable between Estonia and Finland was damaged in December, the Joint Expeditionary Force, a group of northern European and Baltic states led by the UK, responded by activating Nordic Warden, a reaction system that uses AI to track locations of the shadow fleet.
A senior serving British military figure added: “There should be no doubt, there is a war raging in the Atlantic. This is a game of cat and mouse that has continued since the ending of the Cold War, and is now heating up again. We are seeing phenomenal amounts of Russian activity.”
The Russian underwater research programme is largely overseen by the Main Directorate for Deep-Sea Research (Gugi). Its best-known vessel is the spy ship Yantar, which gained notoriety last year when it appeared off the British coast.
It is equipped with unmanned underwater vehicles (UUVs) and two mini-submarines capable of reaching depths of 6,000m, craft that allow the Yantar to find and map infrastructure, as well as to cut cables using manipulator arms or tap them for information.
In November, the Yantar was found in the Irish Sea loitering near cables carrying data for Microsoft and Google. The Proteus was one of several vessels dispatched to monitor it – or, as a defence source describes, it show Russia “they were pissing in our backyard.”
When the Yantar returned to the English Channel in January, the defence secretary John Healey authorised HMS Somerset and HMS Tyne tracked it at closer range, while HMS Astute, a nuclear-powered submarine, covertly monitored the vessel from below before surfacing alongside it.
This more aggressive posture has been widely welcomed in the navy, with a senior official stating: “We’ve got to play by the rules of the game. But whereas before we were playing it nicely, now we’re being more muscular.”
However, the Yantar is not where the real problem lies. The waters immediately encircling Britain sit for the most part on the European continental shelf, meaning they are seldom deeper than 300m. The navy has several ways of monitoring them and is confident it can keep tabs on Russian activity.
But where the continental shelf ends, the sea bed drops thousands of metres. The Proteus is the only navy surface vessel truly capable of policing these depths, where Gugi’s most potent threat, its fleet of six-nuclear powered mini-submarines, could be lurking.
The mini-subs can sit on the sea bed and have manipulator arms capable of cutting cables, laying explosives or placing taps on fibreoptic cables for hacking purposes. They are supported by two larger “mother” submarines, meaning they can be moved covertly to pretty much anywhere in the world.
Russia has other capabilities. Three senior defence sources have revealed that prior to the full invasion of Ukraine, there was credible intelligence that superyachts owned by oligarchs may have been used to conduct underwater reconnaissance around Britain.
Several of these vessels have moon pools that can be used covertly to deploy and retrieve deep-sea reconnaissance and diving equipment.
A former minister also recounted how, in 2018, HMS Albion, an amphibious assault ship, had been forced to leave port prematurely while moored in Limassol, Cyprus. The vessel had been docked for under 24 hours when a huge superyacht belonging to an oligarch pulled up alongside it. Suspecting that it was there covertly to surveil the Albion, the navy ship “moved on quite quickly.”
Sea-bed warfare
The Nord Stream attack highlighted the fragility of the UK’s energy supply, almost a fifth of which now comes from offshore wind farms.
The electricity generated by these turbines is transported to the mainland through undersea cables. Oil and gas pipelines are also vital to Britain, particularly those ferrying gas from Norway. They could easily be severed were Russia to plant explosive devices, such as shaped charges or mines.
“You cut those and you’ve lost that energy — and in the winter during high usage, that could be serious,” a senior military figure said. A second added that a co-ordinated attack could lead to a “failure of the national grid”.
The 60 internet cables that connect Britain to the rest of the world are coated in plastic polyethylene and only a few inches thick. They are easily cut and most of their locations are recorded publicly. However, navy sources said the private companies operating them have laid so many that there is enough “redundancy” in the system to recover quickly from all but the most severe attacks.
The ones that trouble the UK government most are used to transfer banking data across the Atlantic and are integral to the functioning of western financial markets. Satellite back-ups would not be able to handle the huge volume of information that flows through them every second of every day.
The government started to worry about these vulnerabilities a decade ago, when George Osborne’s Treasury received a research paper from a young financier called Rishi Sunak, who had recently joined the Policy Exchange think tank. Secretive work was commissioned on how these cables could be better protected, but the answers were deemed to be in the “too-difficult category”, according to sources. Sunak’s paper would not be published until 2017, several years later.
What troubles the military more profoundly is the ability of Russia to map, tap into or destroy military cables vital to its operations around the world. “There are cables that are not public,” said one senior source. “The Russians have the capability to cut military cables.”
Before the visit to the Proteus, two senior UK sources told The Sunday Times that in around 2020, Russian UUVs — remotely operated and capable of operating at deep depths and travelling for hundreds of miles for days at a time — were found next to sensitive underwater cables. There was no mothership or submarine near by, suggesting they had travelled a great distance to reach the cables.
The Ministry of Defence deemed it “beyond reasonable doubt” that the UUVs were attempting to hack the cables, although no evidence to date suggests Russia has succeeded.
However, it has uncovered proof of other Russian activity that is altogether more disturbing.
Hiding in plain sight
In recent years, the navy has found a number of sensor devices in the seas around Britain.
The Ministry of Defence believes they were planted there by Moscow in order to detect the movements of Britain’s four Vanguard submarines, which together make up the UK’s constant at-sea nuclear deterrent.
After leaving Faslane in Scotland, the submarines “vanish” and are supposed to be invisible from enemy states for the entirety of their deployment, which is typically 90 days or more.
It is not clear what type of sensors were found. Several had washed up on the shore, but more have been identified using the Royal Navy’s fleet of mine-hunter vessels. As they searched, the navy found other sensors it did not know were there, The Ministry of Defence said the at-sea deterrent remains “undetected.”
Whether the UK has discovered evidence of other Russian activity is top secret. “It’s a bit like the space race,” said one senior UK source. “This is a world clouded in secrecy and subterfuge, it’s very hard to get absolute clarity. But there’s enough smoke to suggest something is on fire somewhere.”
Catching up
In 2021, the Integrated Review — a master document outlining the UK’s national security and foreign policy aims after Brexit — committed to purchasing a surveillance ship to protect the UK’s critical underwater infrastructure and to allow the authorities to better understand the scale of the threat.
Two years later, the MoD bought a Norwegian deep-water offshore support vessel, the Topaz Tangaroa, for £70 million. It was modified and renamed the Proteus before becoming operational in October 2023.
The ship has a permanent crew of about 30 civilian sailors from the Royal Fleet Auxiliary (RFA), the merchant arm of the navy, but is ultimately run by specialist naval teams. Life on the Proteus is demanding and the ship is expected to be at sea 330 days a year.
A week before The Sunday Times visit, members of the navy’s mine-hunting and threat-exploitation teams had embedded for the first time. Among them was X-Ray Squadron, which uses autonomous underwater vehicles for mine-hunting, as well as identifying and destroying threats.
During our visit, the teams were training with one of their newest assets: the SeaCat, a cutting-edge 3m-long, torpedo-shaped autonomous vehicle. It has a high-resolution camera on its nose and advanced sonar systems on its sides like wings.
It is capable of running for 24 hours at depths of 300m and one of the commanding officers says it is typically between “three and six times quicker” at hunting mines than conventional methods.
Nearby, another team is preparing the Gavia, a UUV that can plunge 1,000m, deep enough to cover most of the waters surrounding the UK.
Then there is the Defender, which can be fitted with an array of equipment, including manipulator arms. Porton Down, the military’s top-secret research facility, has been developing arms capable of handling and planting shaped charges, a precision explosive that can be used to disable enemy mines.
This capability was tested recently off the coast of Norway, where the Proteus was sent to coincide with a visit by John Healey, the defence secretary, who is negotiating a deal with Oslo to work more closely together to counter the Russian threat.
All three vehicles also have sophisticated sonar systems to scan large areas of sea bed. If they find suspicious activity, they can be sent closer to capture high-resolution images.
Captain Simon Pressdee, one of the senior officers on the visit, said: “Our role is to both defeat any threats to the UK as well as take it out of the greyzone. We do the latter by understanding who is involved and providing that evidence to avoid misunderstandings and make those who threaten the UK accountable for their actions.”
The Proteus has other assets that are able to delve to the deepest part of the ocean, although these were hidden away on the visit.
Future-proofing
With the government committed to spending 2.5 per cent of GDP on defence by 2027, further investment in sea-bed warfare is coming.
The strategic defence review, commissioned by Healey to plug the gaps in Britain’s armed forces, is expected to recommend sharper focus on underwater infrastructure.
Ministers have already accelerated the roll-out of the navy’s first autonomous mine-hunting vessel, the Ariadne and are rolling out a cutting-edge unmanned submarine under a programme called Project Cetus. The purchase of another Proteus-style ship is also being discussed. “Our adversary has multiple points of action that they can be playing, and we’ve only got one ship that can deal with it,” one insider said.
As part of the review, the navy has proposed a new programme, Atlantic Bastion, which will develop a new fleet of air, surface and submersible vehicles, as well as sensors, to police British waters and the wider north Atlantic. In the shorter term, a project codenamed Cabot will get these capabilities up and running in partnership with private industries that rely on underwater infrastructure. This is likely to mean companies are asked to help fund operations, sources said.
A similar idea has been pushed for years by Anne-Marie Trevelyan, the former Tory transport secretary and defence minister. “If this is a national endeavour, it is perhaps time to consider legislating for a level of assured protections of our energy, water, subsea cables … by asking everyone to chip in to the costs,” she said. “A hypothecated tax paid into a defence fund, which can provide protections and deterrence from those who wish our economic security and way of life harm, must be the way.”
An MoD spokesman said: “We are committed to enhancing the security of critical offshore infrastructure. Alongside our NATO and Joint Expeditionary Force allies, we are strengthening our response to ensure that Russian ships and aircraft cannot operate in secrecy near the UK or near NATO territory, harnessing new technologies like AI and coordinating patrols with our allies. And our continuous-at-sea nuclear deterrent continues to patrol the world’s oceans undetected as it has done for 56 years.”
Privately, some in the navy think the UK needs to go further and restore its capability to lay sea mines, something it has not done since the end of the Cold War.
The last stockpiles were dispensed with in 1992, due to the ethical concerns of successive governments and the belief they were redundant. However, Australia has recently pledged £500 million for sea mines, and the Russian threat has reopened the question in the minds of some personnel. Poland and the Baltic states recently announced plans to withdraw from a treaty banning anti-personnel mines.
The navy is not considering this at present and no proposal has been put forward as part of the strategic defence review. But one official, speaking anonymously, said the UK may well need to be able to lay defensive fields around British waters to keep out enemy submarines.
Sir Keir Starmer’s government has clearly realised the scale of the threat, with billions of pounds of extra defence spending putting Britain closer to a war footing.
Given what is happening beneath the waves, that investment is needed now more than ever.
