Russia is stepping up undersea operations around the UK

Russia

Rising covert submarine activity targets cable networks as analysts warn of gaps in Western deterrence

RUSSIAN maritime activity around the UK has increased sharply, with defence officials warning that Moscow is mapping critical undersea infrastructure as part of a wider campaign to probe Western vulnerabilities.

A new Sibylline special report highlights a recent covert submarine operation in UK waters – tracked over a month by the Ministry of Defence – as evidence of an intensifying grey-zone threat focused on subsea cables and energy pipelines that underpin Britain’s economy and security.

“Russian maritime activity near UK waters has increased by around 30% over the last two years,” says Annabelle Walker, associate analyst at Sibylline.

The operation involved a sophisticated deception tactic, with an Akula-class attack submarine acting as a decoy while specialised deep-sea vessels operated near fibre-optic cables and gas pipelines in the North Atlantic. The Sibylline report says the vessels were conducting “nefarious activity” around critical infrastructure before withdrawing without causing damage.

Analysts say the absence of damage should not be taken as reassurance. The activity was almost certainly aimed at identifying vulnerabilities for future sabotage rather than immediate disruption.

“At this stage, we’re still at the mapping phase – identifying vulnerabilities and probing weaknesses in Western monitoring capabilities,” says Karan Vissil, a Eurasia analyst at Sibylline.

That activity reflects a long-standing Russian doctrine that treats seabed warfare and economic disruption as integral to conflict, rather than a new response to the war in Ukraine.

The focus on subsea infrastructure reflects its growing importance. Fibre-optic cables carry most global data traffic, while offshore pipelines and energy links are critical to national supply. Both are difficult to monitor and slow to repair if damaged.

“We assess that grey-zone activity will increasingly be conducted in the maritime domain, where Russia’s capabilities are among the most sophisticated,” Walker says.

Moscow’s advantage lies in a combination of specialised military assets and a growing network of civilian vessels that can be used for deniable operations. The report highlights platforms linked to Russia’s Main Directorate for Deep Sea Research – known as GUGI – capable of operating at extreme depths and interacting directly with subsea infrastructure.

Alongside these assets, Russia’s so-called shadow fleet – a vast network of tankers and civilian vessels with opaque ownership structures – provides a parallel means of conducting surveillance and potential sabotage while maintaining plausible deniability.

“That still falls in the realm of grey-zone intimidation rather than overt sabotage,” Walker says. “But civilian vessels remain an avenue through which more deniable operations can be conducted.”

By contrast, the presence of dedicated military platforms near critical infrastructure leaves far less ambiguity, narrowing the space for plausible deniability in the maritime domain.

Analysts warn these vessels could be used for activities ranging from rudimentary cable interference to more sophisticated operations involving unmanned systems, including aerial and underwater drones.

The UK is seen as a particularly attractive target.

Already widely regarded as Russia’s principal adversary in Europe, having galvanised the continent’s response to the invasion of Ukraine, it also sits at the centre of transatlantic cable networks, while waters around Ireland – through which a significant proportion of global subsea cables pass – represent a critical chokepoint.

“The UK and Ireland are particularly exposed given their geography and limited naval capabilities,” Walker says.

This exposure is compounded by gaps in maritime monitoring and defence capacity, with years of underinvestment leaving Western navies struggling to keep pace with the scale of the threat.

Ireland’s newly launched National Maritime Security Strategy reflects growing recognition of that risk, aiming to expand naval capability and deepen co-operation with the UK and France, particularly in protecting subsea infrastructure and countering activity linked to Russia’s shadow fleet.

However, the scale of the challenge is stark. Plans for an additional 12 vessels will take years to realise. In the meantime, personnel shortages mean Ireland can currently deploy only two naval vessels at sea at any one time, leaving large areas of its waters lightly monitored.

“There has been a steady decline in conventional capabilities across Western militaries, which affects deterrence,” Vissil says.

The result is a growing imbalance between Russia’s ability to operate in the subsea domain and the West’s ability to detect, deter and respond. While surveillance efforts and NATO coordination are increasing, they are unlikely to close the gap in the near term.

For now, the activity remains below the threshold of open conflict. But both analysts caution that the line could shift rapidly if Russia moves beyond reconnaissance.

“A coordinated attack on subsea cables would represent a serious escalation, with potentially significant economic consequences,” Walker says.

Even a limited disruption could trigger communications outages, disrupt financial systems and affect energy flows. A coordinated strike could degrade connectivity across multiple regions.

Yet the ambiguity that defines grey-zone operations remains central to Russia’s approach. By operating below the threshold of war – and often through civilian or deniable means – Moscow complicates attribution and delays decision-making in Western capitals.

Despite growing awareness of the threat, analysts warn there remains a disconnect between official posture and operational reality.

“There is a gap between the level of government concern and the reality of what can be done in terms of response – particularly given limited naval capabilities,” Walker says.

Russia’s approach, analysts say, is not only about targeting infrastructure but about testing Western cohesion.

“Russia is testing unity and cohesion within the NATO bloc, pushing the limits on the assumption that there won’t be a coordinated response,” Vissil says.

“The key question is how governments choose to respond – and whether plausible deniability makes it easier to delay that decision.”

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