Two fibre-optic undersea cables in the Baltic Sea were severed on Sunday and Monday, raising suspicions over a Chinese cargo vessel, which the Danish navy is currently shadowing through the Kattegat strait between Denmark and Sweden.
The Chinese vessel, which departed Ust-Luga port in Russia on Friday last week and appeared to pass over the area where the incidents occurred, has been labelled “of interest” by Swedish police, who are looking into the incident.
Swedish Prime Minister Ulf Kristersson said on Wednesday that the incident must be investigated, adding: “We have seen sabotage in the past, so we take it very seriously.”
This is just the latest in a series of incidents involving pipelines or cables in the Baltic Sea in the past couple of years. So what is happening in the Baltic Sea, and what role does underwater sabotage play in international conflict?
What other damage has been caused to pipelines and cables in the Baltic Sea?
The deep, dark, brackish expanse of the Baltic Sea bed has become a hotbed of geopolitical machinations since two Nord Stream gas pipelines, which are owned by a consortium of energy companies including Russian gas giant Gazprom and which run from Russia to Germany, were rocked by explosions in September 2022.
More than two years later, despite plenty of finger-pointing, no one has taken responsibility for the blasts.
The explosions ruptured the Nord Stream 1 pipeline, which had begun operations in 2011 and which Russia had shut down just weeks before the explosions.
They also damaged the Nord Stream 2 pipeline, which had never entered service because Germany had withdrawn its certification after Russia’s full-scale invasion of Ukraine in February 2022.
Each of the pipelines contains two pipes; the blasts left three out of the four inoperable.
Some Western officials blamed Moscow for destroying the pipes.
In April 2023, a joint investigation by the public broadcasters of Sweden, Denmark, Norway and Finland claimed that Russia had deployed a fleet of suspected spy ships in the Baltic Sea to carry out sabotage operations.
Moscow, in turn, accused the United States and its allies, while German and US media outlets reported that pro-Ukrainian actors may have played a role.
Tensions have only increased since.
Just over a year after the Nord Stream pipeline explosions in October 2023, the Balticconnector gas pipeline connecting Finland and Estonia – jointly owned by Estonian electricity and gas system operator Elering and Finnish gas transmission system operator Gasgrid – was damaged in an undersea incident. Nearby data cables were also reported to have been ruptured.
Investigators in Finland and Estonia alleged that a Chinese container ship dragging its anchor along the sea bed had caused the damage, which took six months to repair. They did not state whether they believed the damage was intentional.
Why would the Baltic Sea be an underwater sabotage hot spot?
In short, geography.
The sea has a shallow and narrow basin, three chokepoints, and is surrounded by eight NATO countries.
It also borders Russia, with Saint Petersburg, the country’s second largest city, nestled in the eastern corner of the Gulf of Finland and its Baltic Fleet located in the Kaliningrad enclave.
Tormod Heier, a professor at the Norwegian Defence University College, told Al Jazeera that post-Cold War tensions in the region began in 2004 with the accession of the three Baltic states – Estonia, Latvia and Lithuania – to NATO.
He said little consideration was given in the West to how, without any buffer zone, the alliance could “credibly defend the three small Baltic states in NATO”.
As Russia became “more assertive and challenged the liberal Western world order”, the Baltic Sea region became the alliance’s “Achilles’ heel”, Heier said.
Russia’s full-scale invasion of Ukraine in 2022 and the accession of Sweden and Finland to NATO in 2024 have further ratcheted up tensions.
Finland shares a 1,340km (832-mile) border with Russia and, with its entry, doubled NATO’s border with Russia and squeezed its coastal access to St Petersburg.
Are these underwater incidents definitely sabotage?
It’s impossible to know for sure, but experts say it is likely.
Underwater sabotage is a method of what is known as “hybrid warfare” – a military strategy that makes use of both conventional and unconventional means to cause instability in regions or countries without giving the appearance of an all-out war.
Hybrid warfare is not new in the region – from GPS jamming over the Baltic states to Russian spy planes veering into Swedish airspace over the Baltic Sea.
Heier says the advantage of hybrid warfare is that it is difficult to attribute directly to one actor.
This means the murky waters of the Baltic Sea provide the perfect “grey zone” in which the indirect, ambiguous nature of a pipeline or cable sabotage incident would still be considered below the “threshold” for outright war.
The facts surrounding this week’s incident remain “murky” and it is simply “too early to rule in or rule out sabotage”, Charly Salonius-Pasternak, a senior research fellow at the Finnish Institute of International Affairs, told Al Jazeera.
He said a range of accidents can cause underwater incidents, adding: “You have oil-laden ships who have no idea how shallow and complex the Baltic Sea is to operate in.”
More than 2,000 vessels traverse the Baltic Sea daily, and the number of larger vessels, including tankers, has increased over past decades as international trade in the region has flourished.
There has also been an increase in “dark ship” activity since Western countries imposed sanctions on Russia after its 2022 invasion of Ukraine.
A “dark ship” is a vessel that turns off the signal system that transmits its position coordinates, often in order to circumvent sanctions.
Heier said that to determine the likelihood of sabotage, it is important to consider whether an actor has a “plausible intention” to severe a cable and whether a pattern emerges from these incidents.
Many Western leaders believe a pattern is forming, including Lithuania’s Minister of Foreign Affairs Gabrielius Landsbergis, who quipped on X on Wednesday: “If I had a nickel for every time a Chinese ship was dragging its anchor on the bottom of the Baltic Sea in the vicinity of important cables, I would have two nickels, which isn’t much, but it’s weird that it happened twice.”
Salonius-Pasternak said determining whether an incident such as Monday’s cable severing was an accident would require time and expertise.
Professor Ashok Swain, who heads the Department of Peace and Conflict Research at Uppsala University in Sweden, told Al Jazeera that it should also be carried out by a neutral body.
He said individual states have taken responsibility for investigating incidents so far, which raises questions of bias and allows different parties to blame each other.
Sweden, Denmark and Germany launched three separate investigations into the Nord Stream pipeline explosions in 2022.
Germany’s is continuing, but the two Nordic countries have closed their cases with no one identified as responsible.
So, if it is underwater sabotage, who could be carrying it out?
The nature of this form of hybrid warfare means every country has its own version of the story, Swain said.
After the Nord Stream blast, some US and European officials initially insinuated that Moscow had blown up the pipelines.
Russian President Vladimir Putin, however, blamed the US and its allies for blowing them up. Russia’s defence ministry at one stage levelled the blame specifically on British navy personnel.
In the most recent incident, Swedish police said a Chinese vessel called Yi Peng 3 was “of interest” and launched an investigation.
Regarding the Chinese ship Yi Peng 3:
The Danish Defence can confirm that we are present in the area near the Chinese ship Yi Peng 3. The Danish Defence currently has no further comments. https://t.co/11s3yeR4PB— Forsvaret (@forsvaretdk) November 20, 2024
One communications cable that was severed ran from the Swedish island of Gotland to Lithuania, while the other ran between Finland and Germany.
According to maritime data, the Chinese ship appeared to have been passing above the two cables when they were severed. Possible motives are unclear.
How is underwater sabotage carried out?
It depends on the incident.
Seismologists in Denmark and Sweden suggest that the Nord Stream pipeline explosions produced sizeable blasts equal to ones that might be produced by 100 kilogrammes of dynamite.
The Swedish investigation did find traces of explosives on several objects recovered from the explosion site.
The Wall Street Journal published a report in 2024 which suggested that a six-member Ukrainian sabotage team, including trained civilian divers, could have been responsible for the blasts.
The report alleged that Ukrainian President Volodymyr Zelenskyy had initially approved the plan until the US’s CIA intelligence agency found out about it and asked him to stop. However, his then commander-in-chief, Valerii Zaluzhnyi, still ordered it to go ahead. Kyiv has denied any involvement.
German media has since reported that Berlin asked Polish authorities to arrest a Ukrainian diving instructor who is alleged to have been part of a team that blew up the pipelines.
Although descending about 80 metres (260 feet) underwater is not impossible, it would require significant diving expertise, Salonius-Pasternak, who has previously dived in the sea himself, remarked.
He explained that the seabed can be very unforgiving and cold, with poor visibility. “It’s not necessarily a place where you can suddenly jump from some little boat and dive and be successful with explosives.”
Anchor dragging, whether intentional or not, has also been posited as a theory for the 2023 damage to cables between Finland and Estonia as well as for the communication cables severed on Sunday and Monday.
How much danger do these underwater incidents pose?
Very little.
Heier said that all the affected countries have a high level of redundancy – additional or backup systems available in case of cable or pipeline damage. As a result, there has been very little disruption to communications or energy supply.
Heier said that in the case of the latest cable ruptures, the Nordic countries can “easily reroute their digital traffic along other fibre cables, without any degradation of the services”.
Salonius-Pasternak said the latest incident has only served as a further reminder to NATO countries around the Baltic Sea that “redundancy is a key factor in resilience”.
If it poses little risk, what is the advantage of underwater hybrid warfare?
To cause anxiety and to spread fear.
Heier said that if malign actors are targeting NATO countries, their aim is to disrupt political and social cohesion.
He said underwater sabotage, where even a powerful coalition such as NATO struggles with “situational awareness”, can provide a “low-risk and accessible” tool to chip away at social cohesion among member states.
