Russian specialist submarines have been used to survey critical undersea infrastructure in and around British waters, part of a broader campaign of activity that European and American officials describe as hybrid warfare, according to a report published by the Congressional Research Service.
The report, numbered R49134 and released on 11 August 2026, was coordinated by Andrew S. Bowen, an analyst in Russian and European affairs, and written alongside colleagues covering European affairs and cyber and information operations. It draws together official statements, national threat assessments and academic work to give Members of Congress an overview of what Russia has been accused of doing across Europe since the full-scale invasion of Ukraine in 2022.
On the undersea question, the report cites the British government’s disclosure in April 2026 of a covert Russian effort, in its words, “to conduct hybrid warfare activities against the UK and its Allies”, using specialised submarines to survey critical undersea infrastructure, possibly in preparation for future sabotage. Then-Defence Secretary John Healey addressed the Russian president directly at the press conference announcing the operation, saying: “And to President Putin, I say this: we see you, we see your activity over our cables and pipelines. And you should know that any attempt to damage them will not be tolerated, and will have serious consequences.”
The vessels involved belong to Russia’s Main Directorate of Deep Sea Research, known as GUGI, a specialist branch of the Russian military that sits directly under the Ministry of Defence and separately from the Russian Navy. GUGI operates a range of specialised submarine, undersea and surface vessels, and its primary missions are reconnaissance and maritime intelligence collection, including surveillance of foreign naval assets and the management of underwater surveillance systems. It may also have the capability to sever or disable undersea infrastructure, the report states.
Concern about the seabed is not confined to British waters, as American and NATO authorities alerted allies in 2023 and 2024 that Russia was actively mapping undersea infrastructure, and news reports identified at least six instances of suspected sabotage or disruption to cables in the Baltic Sea across December 2025 and January 2026. In several cases vessels are alleged to have dragged anchors across the seabed. Finnish authorities detained a cargo ship flying the flag of St Vincent and the Grenadines in December 2025 on suspicion of damaging a telecommunications cable linking Finland and Estonia, a year after seizing a Cook Islands-registered oil tanker that had departed the Russian port of Ust-Luga and was suspected of damaging several data cables and a power cable on the same route. Criminal charges followed against several of that ship’s officers.
Two incidents have been linked to vessels registered in China, though some observers suspect Russian intelligence services rather than the Chinese government were behind them. When cables connecting Lithuania to Sweden and Germany to Finland were cut within hours of each other in November 2024, German Defence Minister Boris Pistorius said: “No one believes that these cables were cut accidentally.” The earlier damage to the Balticconnector pipeline between Estonia and Finland in October 2023 was later acknowledged by China’s government as having been caused by the anchor of a Hong Kong-flagged cargo ship, which Beijing attributed to a storm. Regional officials have expressed scepticism about that explanation.
Speaking in May 2026, Anne Keast-Butler, Director of GCHQ, said: “Russia is scaling up its daily hybrid activity against the UK and Europe, stretching from the seabed to cyberspace, relentlessly targeting critical infrastructure, democratic processes, supply chains and public trust.”
NATO’s response has included Baltic Sentry, launched in January 2025 to increase the alliance’s presence in the Baltic Sea and improve its ability to protect undersea infrastructure. The alliance has also stated that hybrid threats could trigger Article 5 of the North Atlantic Treaty, under which an armed attack against one member is considered an attack against all. Russia routinely denies responsibility for suspected attacks, and the report notes that definitive attribution is often difficult or impossible to prove, with some cases well documented and others resting on circumstantial evidence.
