Baltic Sea undersea ‘sabotage’ sets stage for escalating NATO-Russia contest

LONDON — A spate of alleged sabotage operations against undersea cables in the Baltic Sea has raised the prospect of a dangerous 2025 in NATO’s northern theater, with allied leaders vowing closer surveillance of and tougher action against Russian- and Chinese-linked and other ships accused of nefarious efforts there.

“NATO will enhance its military presence in the Baltic Sea,” alliance chief Mark Rutte said in late December, after the last such instance of suspected sabotage, condemning “any attacks on critical infrastructure.”

Rutte’s commitment came after the most recent of three alleged sabotage operations in the Baltic Sea — the damaging of the Estlink 2 power cable and four internet cables on Christmas Day. The Estlink 2 cable — along with the Estlink 1 cable — transfers electricity from Finland to Estonia across the Gulf of Finland.

Finnish authorities quickly seized control of the ship suspected of the damage to the Estlink 2 cable — the Eagle S. Though flagged in the Cook Islands, Finnish and European Union authorities said the Eagle S is part of Russia’s so-called “shadow fleet” of tankers.

On Jan. 3, Finnish authorities said repair work on the cable had begun and forensic samples would be taken as part of the investigation. Eight sailors were still under a travel ban as the probe continued, they added.

NATO accuses Moscow of using tankers and other vessels to evade an international sanctions campaign on its fossil fuel exports prompted by the Kremlin’s 2022 invasion of Ukraine. The Atlantic Council described this “shadow fleet” as made up of ageing vessels often sailing without Western insurance, under opaque ownership and with regularly changing names and national registrations.

Allied officials say some of the ailing ships are doubling as low-tech saboteur vessels.

There may be as many as 1,400 ships in Russia’s shadow fleet, according to the Windward maritime risk management firm. In December 2023, the energy cargo tracking company Vortexa calculated that 1,649 vessels had operated in what the Atlantic Council called the “opaque market” since January 2021, among them 1,089 carrying Russian crude oil.

Cat-and-mouse at sea

December’s round of suspected sabotage prompted the UK-led Joint Expeditionary Force — a defensive regional bloc also including Denmark, Estonia, Finland, Iceland, Latvia, Lithuania, the Netherlands, Norway and Sweden — to launch an advanced AI-assisted reaction system to “track potential threats to undersea infrastructure and monitor the Russian shadow fleet.”

A Jan. 14 meeting of NATO’s Baltic states in Helsinki, meanwhile, will focus on “measures required to secure the critical underwater infrastructure,” Finnish President Alexander Stubb said, and the “strengthening of NATO’s presence in the Baltic Sea and responding to the threat posed by Russia’s shadow fleet.”

But allies face a major challenge in surveilling some 145,560 square miles of sea crisscrossed by as many as 4,000 ships per day.

NATO tracking efforts are complicated by “the sheer scale of the global commercial shipping sector and the fact that ownership structures are often quite opaque and complex,” Sidharth Kaushal — the sea power senior research fellow at the British Royal United Services Institute think tank — told ABC News.

“A vessel may have multiple beneficial owners, its owners may not necessarily be from the state where it’s registered and so actually attributing its activity to a given state becomes very difficult,” he explained.

Russian- and Chinese-linked vessels could play a role, but so could ships seemingly unconnected to Moscow or Beijing.

“The Russians have quite a broad spectrum of commercial vessels to choose from,” Kaushal said. “It’s actually quite odd, in some ways, that they opted for a vessel that’s associated with their shadow fleet.”

The Baltic Sea is also relatively shallow. Its average depth is around 180 feet, compared to 312 feet in the North Sea and 4,900 feet in the Mediterranean Sea.

Reaching cables or pipelines at the bottom of the Baltic is far easier than in the world’s largest bodies of water, like the Atlantic Ocean with its average depth of 10,932 feet or the Pacific Ocean at 13,000 feet.

“In the Atlantic, for example, one has to use some pretty specialized equipment to go after undersea infrastructure,” Kaushal said. In the Baltic, “much simpler tools — things like dragging an anchor — are perfectly feasible means of attack.”

NATO’s toolbox

Guarding specific sites appears more realistic than identifying and surveilling all potential saboteurs. After the damage to Estlink 2 was reported, for example, Estonia said it dispatched naval vessels to protect Estlink 1.

November’s Bold Machina 2024 naval exercise in Italy also saw special forces divers test underwater sensors that NATO said could one day be used to protect underwater infrastructure.

“That’s the only way to narrow the problem — to focus on the critical infrastructure, rather than trying to achieve wide area surveillance over an area like the Baltic,” Kaushal said.

But NATO ships will still be limited in what action they can take to stop damage occurring. “International freedom of navigation limits what navies can do on international waters, or even within their own exclusive economic zone,” Kaushal said.

The United Nations Convention on the Law of the Sea does note that freedom of navigation may be challenged if a ship’s passage “is prejudicial to the peace, good order or security” of coastal states.

Historic agreements — like the 1884 Convention for the Protection of Submarine Telegraph Cables — might also offer allies some latitude to act against suspect vessels.

But challenging the passage of civilian shipping might have unwelcome consequences elsewhere. More muscular policing by NATO in the Baltic might encourage more assertive Chinese naval activity in the South China Sea, for example, or encourage more Iranian interdictions in the Persian Gulf.

“I think that’s something that nations, particularly Western nations, have shied away from,” Kaushal said.

Local allied leaders, at least, appear to be clamoring for action. December’s alleged attack is only the most recent of a spate of suspected sabotage incidents in the Baltic.

In November, two intersecting submarine cables — the BCS East-West Interlink connecting Lithuania to Sweden and the C-Lion1 fiber-optic cable connecting Germany to Finland — were damaged in the Baltic Sea.

Authorities suspected the Chinese-flagged cargo ship Yi Peng 3 of causing the damage. German, Swedish, Finnish and Danish officials boarded the ship off the Danish coast to inspect the vessel and question the crew. The Yi Peng 3 later set sail for Egypt.

The first notable alleged cable sabotage incident in the Baltic Sea occurred in October 2023, when the Hong Kong-flagged Newnew Polar Bear vessel dragged its anchor across and damaged the Balticconnector gas pipeline linking Estonia and Finland. The nearby EE-S1 telecoms cable was also damaged.

Investigators recovered a damaged ship’s anchor from the seabed close to the damaged cables, with gouge marks on either side of the cables indicating its trajectory. Finland’s National Bureau of Investigation said the Newnew Polar Bear was missing one of its anchors.

In August, the Chinese government admitted that the vessel damaged the underwater infrastructure “by accident,” citing “a strong storm.”

2025 in the Baltic theater

Even before ships began damaging cables in the Baltic region, the strategic sea — referred to by some allied leaders as the “NATO lake” after the accession of Sweden and Finland to the alliance — played host to covert operations apparently linked to Russia’s war on Ukraine.

The Nord Stream 1 and 2 pipelines carrying natural gas from Russia to Germany were bombed in September 2022, marking the first notable incident of alleged sabotage in the Baltic Sea since Russia’s invasion of Ukraine in February 2022.

The pipelines had long been fiercely criticized by those in North America and Europe skeptical of Berlin’s business dealings with Moscow, particularly leaders in Ukraine and the Baltic region who saw the pipelines as a plank of Russian hybrid warfare.

Investigators are yet to establish who was responsible for the apparent sabotage to the pipelines, with a series of unconfirmed reports variously accusing Russia, the U.S. and Ukraine for the blasts. All have denied involvement.

The Baltic, then, is already an important theater in the wider showdown between Russia and the West.

The potential value for Russia is clear. With a handful of tankers, Moscow can force its NATO rivals to commit significant time and resources to guarding undersea infrastructure. When sabotage does occur, the Baltic’s relative ease of access and the energy needs of regional nations might amplify its impact.

“The gas grid in the area is not particularly well integrated with the rest of the European grid,” Kashaul noted. “In much of Europe, this would be a bit of a nuisance, but in the Baltic Sea limited sabotage — particularly to the gas pipelines — can actually have some pretty disproportionate effects.”

European nations are highly sensitive to gas outages given the knock on economic — and thus polling — effects. Energy insecurity has been one of the major themes undermining the continent’s response to Russia’s war. Moscow has been keen to exploit this weak spot.

But undersea escapades in the Baltic are not necessarily a free hit for Russia.

Moscow’s shadow operators have “thus far enjoyed the freedom of navigation and the ability to move Russian oil at above price cap rates quite freely through NATO controlled waters,” Kashaul said.

If NATO nations can demonstrate that sanctions-busting vessels are involved in sabotage, the ghost ships might yet face more tangible retaliation.

But that too could prompt escalation. A Danish intelligence report cited by Bloomberg, for example, noted that Russia may begin attaching military escorts to tankers transiting the Baltics.

Such a development is “quite plausible,” Kashaul said, though noted the intensity of regular convoy operations may be beyond Russia’s relatively small Baltic Fleet.

A more militarized approach, he added, may also unsettle the non-Russian nationals crewing the vessels.

“Whether the people on those ships want to take the risk, even if the Russians are offering escorts and convoys, is another factor,” Kashaul said.

ABC News’ Zoe Magee and Ellie Kaufman contributed to this report.