By Thomas Grove

GMINA BUDRY, Poland -- In recent weeks, Russian troops carried out a series of military exercises off the coast of Kaliningrad, Russia's exclave surrounded by NATO members.

Moscow's forces practiced using hypersonic missiles to fend off a hypothetical attack by air and sea. The show of force sent a message to its rivals in the region about Russia's capabilities on the Baltic Sea, where the suspected sabotage of undersea cables has highlighted a new theater of confrontation between Moscow and the North Atlantic Treaty Organization.

While Moscow focused on a broader buildup of military strength in Kaliningrad before its invasion of Ukraine, the exclave has redeployed many of its troops and much of its equipment to the front line. The multiweek exercises underscore Kaliningrad's vulnerability at a time when NATO allies have been building up their defenses -- on land and at sea.

Kaliningrad's unusual geography -- as Russia's westernmost territory that shares no borders with the rest of the country -- has made it both a liability and an asset for Moscow. It gives Russia a port on a sea that is otherwise encircled by NATO states and a launchpad for its Iskander missiles within hundreds of miles of European capitals.

"It's clear the Russians use Kaliningrad to exert psychological pressure on the West and NATO," said Konrad Muzyka, director of Poland-based Rochan Consulting, which focuses on the Russian military. "Even though the likelihood is remote, the Iskander is nuclear capable and could be used by the Russians to strike Stockholm, Berlin or Warsaw."

Wrested from Nazi Germany after World War II, Kaliningrad serves as a reminder of the country's military might. It is expected to play a part in next month's 80th anniversary celebrations of the defeat of Nazi Germany, a holiday that has gained center stage under Russian President Vladimir Putin. Local lawmakers have posted videos online of World War II-era songs being piped out over the Kaliningrad capital's redbrick city center.

Slightly smaller than Delaware, Kaliningrad is home to about half a million people. During the Cold War, Moscow filled it with missiles to threaten NATO capitals and sensitive radar equipment to peer beyond the iron curtain.

After the fall of the Soviet Union, the territory was briefly celebrated as a window to Europe. Its flourishing IT sector and visa-free regimes set up along the border promoted travel between Russia and the European Union. But that was shut down amid rising tensions in 2017, before most border checkpoints were closed altogether following the full Russian invasion of Ukraine.

Today, Kaliningrad is once again at the center of tensions in the region. Both of its neighbors -- Poland and Lithuania -- have fortified their borders with Russia since the start of Moscow's war in Ukraine.

On a recent afternoon, Polish Maj. Michal Bednarko surveyed newly dug pits and concrete obstacles, known as dragon's teeth, which are meant to keep Moscow's soldiers and tanks out of Poland. Behind him lay an empty strip of land ready to be mined at the first hint that the Kremlin's troops are preparing an incursion.

"It would be very costly for the enemy to cross this," he said.

NATO is applying pressure by sea too. Kaliningrad is home to the headquarters for Russia's Baltic Fleet, meant to safeguard Russian shipping in the crucial waterway. Russia's so-called shadow fleet, which helps Moscow skirt Western sanctions, delivered some 40% of the country's oil exports via the Baltic Sea last year.

But Russia's fleet on the Baltic is now surrounded by rivals. Two countries with Baltic shoreline -- Sweden and Finland -- have joined NATO's ranks since the start of the war in Ukraine, helping to turn the body of water into what Western officials like to describe as a "NATO lake."

Earlier this year, NATO launched its Baltic Sentry operations, aimed at boosting the alliance's presence in the sea around Kaliningrad. That operation is meant to provide patrols on the shallow waters of the Baltic, where a handful of ships -- some with suspected ties to Russia -- have dragged their anchors and damaged undersea cables and pipelines.

Estonia's Parliament is considering a law that would give its country's defense forces the mandate to sink ships it believes pose a threat to Estonian or NATO critical infrastructure. "Estonia takes suspicious activities in the Baltic Sea very seriously," Estonian Prime Minister Kristen Michal said on X.

Russia has vowed to protect its ships. "If such a law is passed, there will be escorts of our ships. And if they try to sink any so-called suspicious ships, our escorts will answer back," said Kaliningrad lawmaker Andrei Kolesnik.

Western officials say that NATO needs further contingency planning in case tensions in the waterway erupt into hostilities. "The Baltic Sea is far from being safe," said Maj. Gen. Maciej Klisz, operational commander at the Polish General Staff. "We have to control the Baltic Sea, especially Kaliningrad, to be effective against Russians."

NATO is also preparing for possible conflict scenarios by land. Russia would only be able to supply the exclave by sea or air, leading to speculation that Moscow could try to establish a land bridge between Kaliningrad and Russia's ally Belarus, which are separated by 50 miles of NATO territory.

Some analysts expect Moscow to try to make a quick incursion into one of Kaliningrad's NATO neighbors to disable NATO's first line of defense. "If Russians wanted their forces to survive in Kaliningrad, they would have to move into Poland or Lithuania to prevent their destruction and give them more depth to maneuver in," said Muzyka.

That has led Polish military strategists to consider various options to hem in Kaliningrad, including a blockade. Only one underwater fiber-optic cable runs between the territory and St. Petersburg. Likewise, only four vessels ferry military and civilian goods between mainland Russia and Kaliningrad.

"We know the name of each and every captain," said Maj. Gen. Klisz. "You can have a division there, but if you cut them off from the land and sea and leave them without ammo and fuel and food, it's just a bunch of hungry people."

Write to Thomas Grove at thomas.grove@wsj.com

(END) Dow Jones Newswires

April 18, 2025 10:30 ET (14:30 GMT)

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