Russian Ambassador in the UK does not deny the deployment of spy sensors in British waters to track Vanguard-class submarines.

On April 12, 2025, Russia’s ambassador to the United Kingdom, Andrei Kelin, stated publicly that he does not deny the presence of Russian sensors in British waters allegedly used to track Royal Navy nuclear submarines. In a BBC One interview, Kelin responded “No” when asked if he rejected the claims, adding, “I am not going to deny it.” He questioned whether there was any real interest in following what he described as “very old outdated nuclear warheads,” and stated that concerns raised by the UK were “extremely exaggerated.” Pressed further, Kelin said, “This threat has been invented, absolutely, there is no threat at all from Russia to the UK.”
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These sensors are believed to have been planted by Russia to monitor the UK’s four Vanguard-class submarines, which serve as the United Kingdom’s continuous at-sea nuclear deterrent. (Picture source: UK MoD)

The remarks follow a three-month investigation by The Sunday Times that revealed the Royal Navy had discovered Russian sensors hidden in the seas surrounding the UK. Some devices were recovered after washing ashore, while others were located on the seabed by mine-hunting vessels. These sensors are believed to have been planted by Russia to monitor the UK’s four Vanguard-class submarines, which serve as the United Kingdom’s continuous at-sea nuclear deterrent. According to military sources, these findings were classified as a potential national security threat.

The UK Ministry of Defence has acknowledged the threat posed by such activities and confirmed that the continuous at-sea deterrent continues to patrol the oceans undetected. Officials suggest that the devices may have been designed to record acoustic signatures or identify patterns of movement associated with the Vanguard-class submarines. These submarines typically operate undetected for around 90 days per deployment, following departure from HMNB Clyde in Faslane, Scotland.

Military and intelligence officials view the sensors as one component of broader Russian activity described as “greyzone warfare”—operations below the threshold of armed conflict. These include sabotage or surveillance of energy pipelines, telecommunications infrastructure, and undersea cables. In recent months, multiple incidents have raised concerns across Europe. Eleven internet cables in the Baltic Sea have been damaged over the past 15 months. Defense officials believe some damage may have been caused by ship-dragged anchors in deliberate attempts to compromise these cables. In one case, following damage to the Estlink2 cable between Estonia and Finland, the UK activated an AI surveillance system known as Nordic Warden to track potential threats, particularly vessels within Russia’s shadow fleet.

The shadow fleet refers to older or repurposed vessels believed to support Russian operations by operating covertly in international waters. Some of these ships, including the research vessel Yantar, have drawn attention for loitering near UK waters. The Yantar is equipped with unmanned underwater vehicles (UUVs), two mini-submarines capable of descending to 6,000 meters, and robotic arms capable of manipulating or cutting undersea cables. In November, the Yantar was tracked in the Irish Sea near commercial cables used by companies such as Microsoft and Google. The RFA Proteus, a Royal Fleet Auxiliary vessel, was among several British ships deployed to monitor its activities. In January, after the Yantar returned to the English Channel, it was flanked by HMS Somerset and HMS Tyne, while HMS Astute covertly tracked it from below.

UK defense officials report a high volume of Russian underwater activity. Royal Navy personnel have detected unmanned Russian vehicles operating near undersea cables and discovered sensor devices on the seabed around the British Isles. Intelligence also suggests that superyachts owned by Russian nationals may have conducted underwater reconnaissance, using moon pools to deploy or recover equipment. In one instance, HMS Albion left port early in Limassol, Cyprus, after a large superyacht moored nearby, raising concerns of surveillance.

These developments have heightened concern over the security of the UK’s undersea energy and communication networks. Approximately 60 undersea internet cables connect the UK to other nations, including many not publicly documented. These cables are typically coated in polyethylene and only a few inches thick. Energy infrastructure, including pipelines from Norway and offshore wind farms, is also vulnerable. Some UK defense officials have warned that coordinated attacks on these systems could lead to major disruptions, including energy shortages and interruptions to financial data transmission. Satellite systems would not be able to handle the full volume of data currently transmitted via submarine cables.

In November, the Yantar was tracked in the Irish Sea near commercial cables used by companies such as Microsoft and Google. (Picture source: UK MoD)

The Royal Navy’s RFA Proteus, which became operational in October 2023, plays a central role in the UK's efforts to monitor the seabed. The ship is equipped with a moon pool, deep-sea cranes, and remotely operated and autonomous underwater vehicles (AUVs). The vessel houses approximately 30 Royal Fleet Auxiliary crew members and rotating Royal Navy teams. During a recent visit, naval mine-hunting teams operated the SeaCat AUV, capable of running 24 hours at depths of 300 meters. Other systems onboard include the Gavia, which can dive to 1,000 meters, and the Defender, which can carry manipulator arms designed to handle explosive devices or collect samples. These technologies are intended to detect, document, and, if necessary, neutralize threats on the sea floor.

The Ministry of Defence plans to expand these capabilities through Project Cabot, a joint venture between the military and private companies in energy and telecommunications sectors. A longer-term initiative, Atlantic Bastion, aims to establish a network of air, surface, and sub-surface platforms for undersea surveillance and infrastructure protection across the North Atlantic. These efforts may include the purchase of a second vessel similar to Proteus. Other systems under development include Project Cetus, focused on large uncrewed submarines, and Ariadne, an autonomous mine-hunting ship. As part of ongoing discussions, Defence Secretary John Healey visited Norway in February to explore bilateral cooperation in countering undersea threats.

Some military sources have proposed restoring the UK’s capacity to lay sea mines, a capability abandoned after the Cold War. Although no formal policy shift has occurred, other nations such as Australia and Poland have revisited the utility of sea mines in response to modern threats. A senior UK source noted that Britain currently has only one vessel capable of operating at the necessary depths to monitor and respond to Russian mini-submarine activity.

The historic context of Russian operations near British waters is long-standing. During the Cold War, Soviet AGIs (Auxiliary General Intelligence ships), often disguised as trawlers, maintained fixed and area patrols around the UK, including near Malin Head, the Shetland Islands, and the English Channel. These ships deployed hydrophones and sonobuoys to gather acoustic signatures of submarines and to intercept electronic signals. British countermeasures included escort vessels like HMS Sentinel, acoustic masking, and early warning aircraft patrols.

Recent commentary has linked present-day surveillance patterns to these Cold War tactics. Several experts argue that modern operations may involve similar objectives, such as mapping towed sonar arrays, identifying submarine deployment patterns, and disrupting strategic deterrent patrols. Some surveillance buoys, including Soviet Type 75 sonobuoys recovered off the U.S. coast in the 1980s, were known to transmit collected data back to AGI ships for reuse. While Russia denies these activities, UK defense officials and analysts continue to monitor the evolving situation closely.

The Ministry of Defence maintains that the UK's nuclear deterrent remains secure and operational, stating: “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.”