The Øresund Strait, The New Frontier In Russia’s Hybrid War Against NATO

The port and ferry terminal in Helsingborg are bustling with activity. Everything operates with an almost choreographed efficiency. Ferries maneuver slowly; refrigerated trucks wait their turn to board alongside cars, cyclists, and workers who cross the Øresund Strait as if taking a commuter train. After all, only 2.5 miles separate Swedish Helsingborg (population 114,000) from Danish Helsingør. From the waterfront, under the oblique light of northern Europe that lengthens the evenings over the water, the strait is so narrow it is hard to see it as a strategic border. But that maritime line, which looks ordinary on maps, is today one of the flashpoints between Russia and NATO. It is the setting of a gray, hybrid war of maritime sabotage and ghost ships.

The Øresund Strait, also known as the Sound, is one of three gateways from the Baltic Sea to the Atlantic Ocean, along with Denmark’s Great Belt and Little Belt. That means every vessel entering or leaving the Baltic — cargo, energy, oil, data cables, or military — passes through this corridor.

For centuries, controlling Øresund meant controlling access to the Baltic, says Per Svensson, 62. Tanned from his morning walks, he downs a black coffee in a café near the Helsingborg ferry terminal as he recounts working for two decades on the port’s ships. Now he likes to sit and watch the ferries and freighters coming and going — and read about the region’s history. “These waters have always been ordinary to us, not a border. Now everything seems to have changed,” he says, pensive.

Historically, these straits were a source of power and wealth for Denmark, which for four centuries collected maritime tolls. In post–Cold War Europe, that geostrategic significance faded somewhat under decades of Nordic integration, short ferry crossings, and weekend tourism. There are no tolls today. But the strait’s old strategic importance has returned forcefully amid Russian efforts to move the hydrocarbons that fuel its war against Ukraine.

In 2025, Nordic authorities verified the passage of at least 292 vessels linked to Russia in the region. Ships that left Russian Baltic ports transited Øresund or the Great Belt to the North Sea and from there to the Atlantic. From the terrace of the luxury Clarion hotel in downtown Helsingborg, where NATO foreign ministers met last week, you can see those vessels almost every day, says Sweden’s Foreign Minister Maria Malmer Stenergard.

They look like ordinary ships, but beneath a dense layer of bureaucracy they are part of what is called the ghost fleet, or shadow fleet, Malmer Stenergard says. These are aging vessels with opaque ownership structures designed to make them hard to trace, flying flags of distant countries that change frequently — ships the Kremlin and its orbit use to move hydrocarbons. It is their way of evading Western sanctions over the war in Ukraine.

Intelligence reports have also recently documented that many of those ghost ships carry armed contractors on board whose job is to protect the cargo, and who give those vessels a military aura. “You cannot prove they are Russian military, but there is evidence they are linked to paramilitary companies with ties to the Kremlin,” a Swedish official says.

Russia’s war against Ukraine, which shook Europe more than four years ago and changed its landscape and mindset forever, produced a structural shift in the Nordic region that today, under the Kremlin threat, has been hardened. The invasion ordered by Vladimir Putin pushed Finland and Sweden into NATO. Both Nordic countries provide the Alliance with invaluable strategic and geographic capabilities. Their accession, together with the existing membership of Estonia and Denmark, changed the Baltic’s standing. With the exception of the Russian exclaves of Kaliningrad and St. Petersburg, it became an allied sea — almost a “NATO lake,” as experts put it. That raised the value of strategic points such as Helsingborg.

Conflict in the shadows

Far from being placid, the Baltic is now one of the primary laboratories of Russia’s hybrid warfare, says Elisabeth Braw, a researcher at the Atlantic Council’s Transatlantic Security Strategy Center.

There are no fleet battles or classic naval engagements. The Kremlin uses more ambiguous tactics, such as sabotage or damage to maritime infrastructure, interference with navigation systems, manipulation of AIS signals, covert operations that are hard to attribute, and espionage activities.

And at the heart of that hybrid war is the ghost fleet. “Russia has discovered these ships can be used for more than moving oil — to cause damage in the Baltic — so they are exploiting them,” warns Braw, who has extensively researched the Kremlin’s hybrid warfare.

Moscow has found it can inflict substantial damage without using military forces. There is also an environmental risk from those decrepit tankers carrying Russian hydrocarbons. Since October 2023, authorities in the region have recorded at least 11 significant incidents of damage to submarine cables — mainly telecommunications and power lines; some incidents involved gas pipelines and other critical infrastructure, according to an Estonian intelligence report. Although most investigations have not officially attributed the incidents to the Kremlin, several of the most serious cases have involved vessels linked to Russian ports or the ghost fleet.

Ships such as the Fitburg, detained by Finnish authorities in December 2025 after being implicated in damage to telecom cables between Finland and Estonia. The freighter was sailing under the flag of Saint Vincent and the Grenadines, had departed St. Petersburg, and was found with its anchor down in Finnish waters — a pattern that bears a strong resemblance to the Russian shadow fleet.

Thus, Helsingborg, a bottleneck of the Baltic, has shifted from a peripheral, quiet place to an area under watch. The small southern Swedish port city and the Øresund Strait are now part of the Atlantic defensive architecture.

Maritime law establishes that vessels that appear linked to the Russian ghost fleet have the right to sail. And unless there is evidence of environmental risk, illegal fishing, or another crime against maritime traffic, Swedish, Danish, Estonian, or Finnish authorities have limited room to act.

A few months ago, however, the Swedish government enacted a legal change that expands the Coast Guard’s powers to request insurance information and to monitor ships merely transiting Swedish territorial waters and even Sweden’s Baltic exclusive economic zone. “We are not at war, but we are not at peace either,” Prime Minister Ulf Kristersson has said.

Back at Helsingborg’s port, whose terminal almost fronts the terraces of waterfront restaurants and cafés crowded under the May sun, Karin Akerman says she is “a little worried.” The 55-year-old teacher has two teenage grandchildren and fears the war may one day reach her waters. “We always thought we would never experience a conflict, but nothing feels safe anymore,” she says. Nearby, in a small square, two teenagers record a TikTok video. For a couple of days the town’s attraction has been the tide of police and military personnel deployed during the NATO meeting. “Nothing ever happens here. And I don’t think anything will happen,” one of them says.

Not far away, at various points along the Skåne coast, concrete bunkers built during World War II and expanded during the Cold War still face the Sound. For years they were historical, anachronistic remnants of a Sweden on alert when the Baltic was seen as a potential line of confrontation with the Soviet Union. Now, in a country that is continuing to militarize and which talks about submarine cables, maritime surveillance, espionage, and hybrid warfare, they make sense again to many.

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