By Daniel Michaels

ABOARD THE ESPS ALMIRANTE JUAN DE BORBON -- If there are Russian submarines "all over the place" near Greenland, as President Trump has said, the crew of this Spanish frigate aims to find them.

Deep within the warship, behind a locked door in a windowless control room called the Combat Information Center, seasoned sub-hunters listen for sonar pings flagging an undersea target. They stare at screens showing the nearby Norwegian fjords, where five European NATO ships have assembled to practice a complex dance known as anti-submarine warfare. High overhead, military aircraft bristling with antennas and probes scan surrounding waters.

Russia over recent years has ramped up submarine activity in the High North. Trump's push for Denmark to sell Greenland to the U.S. this year drew attention to the Arctic island's significance for defending America and the whole North Atlantic Treaty Organization. While military experts say Greenland isn't a focus of Russian naval activity, there is consensus that Moscow is using its formidable subsea know-how and resources to test Western countries.

In response, NATO on Wednesday announced that it is boosting activity and deepening coordination of national forces in the region, in an effort called Arctic Sentry.

NATO members have already been dusting off sub-hunting skills that got rusty after the Soviet Union collapsed. That is why ships, aircraft and officers from 10 of the alliance's 32 members converged on icy Scandinavian waters to practice sub-hunting for two weeks, in the annual Arctic Dolphin exercise hosted by Norway that ends on Feb. 13.

"The Russians are developing many bases and capabilities that were sort of dormant since the end of the Cold War," said Spanish Navy Rear Adm. Joaquín Ruiz Escagedo, an anti-submarine warfare specialist who commands one of NATO's naval forces and helped lead the exercise.

"We haven't been operating as often as we need to operate together in this region," said Ruiz as he set off from the Norwegian port of Bergen. Deploying a Spanish ship to the High North drives home that point, he said, because Madrid's fleet usually operates farther south.

To help NATO navies cooperate in punishing northern waters, alliance forces are drilling more frequently. In Arctic Dolphin, sub-hunting ships and aircraft were joined by two submarines, from Norway and Germany, aboard which U.S. and Canadian officers are honing their skills. One sub plays the quarry and the other helps hunt.

The hunting ground, in waters west of Norway, is a prime route for Russia's Northern Fleet submarines. Based inside the Arctic Circle, they often head south toward the Atlantic Ocean, potentially nearing the U.S. and most of Europe.

Channels between Greenland, Iceland and the U.K. -- known in NATO parlance as the GIUK Gap -- are getting more attention now than they have at any time since the Cold War. That is because of activity below and above the water, including increased traffic of naval, commercial and scientific vessels from Russia, China and other countries as climate change opens new thoroughfares. The U.S. in 2016 restarted air patrols of the region from Iceland, a decade after closing an American base there.

For Norway -- a founding NATO member that shares a land border with Russia -- renewed alliance attention to the region is a welcomed change.

"We felt a bit alone 10 or 15 years ago, so we are of course happy that the focus is drawn toward the Arctic again," said Royal Norwegian Navy Capt. Jim Robertsen, who heads the country's submarine fleet.

Robertsen said recent political disputes between the Trump administration and allies haven't affected cooperation with the U.S. Navy.

Cooperation is vital because sub-hunting is inherently complex, requiring lots of resources. The ships and sub all survey surrounding waters using their sonar arrays, supplemented by signals from sonar buoys that they and aircraft drop nearby.

High above, crews aboard P-8 Poseidon sub-hunting planes -- specially modified Boeing 737 jetliners like those Southwest Airlines and Ryanair fly -- can peer deep into the sea, launch probes and even fire anti-submarine weapons. Navy helicopters, which can land on the warships and hover just above the waves, scan surrounding waters using equipment including magnetic anomaly detectors that sense metal below.

All that information flows to the Borbón's combat center, where an officer overseeing operations strives to assemble a unified picture from the disparate data. A NATO maritime command center on land crunches the data in parallel. Even with cutting-edge technology, the work is as much art as science.

"There's a reason anti-submarine warfare is jokingly called 'awfully slow warfare,'" said Richard A. Moss, a professor at the U.S. Naval War College's Russia Maritime Studies Institute.

Russia over the past decade has launched increasingly quiet new submarines and refurbished old ones, improving their stealthiness and complicating work for NATO. The U.S. and its allies have, meanwhile, invested in technology and equipment such as the P-8 planes to sharpen both detection and processing of sensor data, "so it goes through cycles of adaptation and counter-adaptation," said Moss.

NATO's European navies, after years of building warships focused on dangers including piracy, smuggling and terrorism, must once again build ones designed for sub-hunting and relearn how to use them, said retired Dutch Adm. Rob Bauer, who was one of NATO's top military officials until last year.

Sub-hunting is difficult in part because seas are vast: If the Arctic Ocean were rescaled to the volume of Russia's largest submarine, that same submarine would be the size of a couple grains of sand.

Add to that complexities of water that confound searching, especially near the Arctic. Factors that vary widely throughout the region -- such as seafloor topography, temperature, salinity and the presence of fresh water from melting ice -- can play havoc with sonar signals. A submarine captain with good knowledge of surrounding seas can use those variations to hide in open water.

U.S. and European sub-hunting veterans say NATO is fairly good at spotting Russian submarines, but that isn't always the issue.

"It's less about 'can they get through' and more about what problems they're trying to create," said David Cattler, a former NATO assistant secretary-general for intelligence and a former U.S. Navy surface warfare and intelligence officer. "Those problems often involve persistent uncertainty, diverting intelligence and reconnaissance resources, and signaling resolve -- rather than preparing for imminent conflict," he said.

During Arctic Dolphin, the hunted submarine went all-out to evade detection, said U.S. Navy Cmdr. Arlo Abrahamson, a spokesman for NATO's Allied Maritime Command, which oversaw the exercise. In some years, the subs have been spotted and in others they evaded detection, he said -- and failure can be more educational than success. He wouldn't say what happened this year.

For Ruiz, the Spanish admiral, the exercise's greatest achievement is refreshing the perishable skill of coordinating resources from so many countries.

"We need to operate more often to upgrade our interoperability," he said. "We have to operate as a single navy."

Write to Daniel Michaels at Dan.Michaels@wsj.com

(END) Dow Jones Newswires

February 11, 2026 12:00 ET (17:00 GMT)

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