The Baltic Sea, long a crossroads of commerce and conflict, is once again at the center of rising geopolitical tension as the Swedish navy reports an unprecedented surge in Russian submarine activity. On December 6, 2025, Capt. Marko Petkovic, chief of operations for the Swedish navy, revealed that encounters with Russian submarines in the Baltic now occur on an "almost weekly" basis—a frequency that has become routine for Swedish forces, according to The Guardian and European Pravda.
"Moscow is continuously reinforcing its presence in the region," Petkovic told reporters, describing the situation as one where sightings of Russian vessels are no longer rare events but an expected part of the navy’s weekly operations. He emphasized, "contacts with Russian submarines are very common" and noted that the number of such encounters has risen sharply in recent years.
Behind these routine sightings lies a deliberate and constant modernization program by Russia. As Petkovic outlined, Russia is now producing one Kilo-class submarine every year at shipyards in St. Petersburg and the Kaliningrad enclave. This steady output is part of what he called a "deliberate and constant modernisation programme"—a phrase that encapsulates the methodical nature of Russia’s naval expansion.
But what’s driving this uptick in Russian naval activity? According to Petkovic, the ongoing war in Ukraine is a key factor, but Sweden’s navy is already looking ahead to what might follow. "Once a ceasefire or armistice is eventually in place in Ukraine, you can only assess, and we do assess that Russia will reinforce its capabilities in this region," he said. The implication is clear: as the conflict in Ukraine cools, the Baltic Sea could become the next arena for Russian military focus. Petkovic concluded, "the [Swedish] Navy needs to continuously grow and focus on the overall picture."
It’s not just submarines that are causing concern. The Baltic Sea region faces a complex web of threats, including suspected drone-based hybrid attacks, alleged sabotage of underwater infrastructure, and the movement of aging "shadow fleet" oil tankers carrying Russian crude through crowded shipping lanes. These tankers, often sailing under civilian flags, have prompted particular unease among Swedish officials. Petkovic warned, "The shadow fleet in itself is not a military problem, but the shadow fleet could affect our nations from a military perspective." He did not rule out the possibility that these ships could be used for launching drones or other forms of covert action.
The situation is being watched closely not only by Sweden but by its neighbors and NATO allies. Germany’s defense minister, Boris Pistorius, has publicly stated that Russia is stepping up hybrid attacks against European states—including in the Baltic Sea—as a way to test their resilience. In June, German Foreign Minister Johann Wadephul described the Baltic Sea region as "a dangerous geopolitical hotspot." Lithuania’s President, Gitanas Nausėda, has also accused Russia of "deliberately stoking tension in the Baltic Sea."
In response to these mounting risks, Sweden recently hosted a major NATO anti-submarine warfare exercise known as Playbook Merlin 25. The exercise brought together nine countries—including Germany, France, and the United States—to practice submarine-hunting and coordination in the Baltic’s notoriously complex underwater terrain. The goal: to prepare for possible attacks on allied vessels or critical infrastructure. According to The Guardian, this exercise is just one example of how regional navies are adapting to a more contested maritime environment.
Another recent initiative is Operation Baltic Sentry, a NATO vigilance activity launched in January 2025 specifically to strengthen the protection of critical undersea infrastructure. Petkovic pointed out a notable success: "Since [Baltic Sentry] was established in January, we haven’t seen any cable incidents in this region at all." This suggests that enhanced vigilance and multinational cooperation are already having a tangible impact on maritime security.
Yet, Russia’s own maneuvers in the Baltic Sea are growing in scale and sophistication. In recent months, the Russian navy launched major exercises involving more than 20 warships, about 25 aircraft and helicopters, and roughly 3,000 personnel. These drills included practicing anti-submarine and anti-drone missions, as well as the military escort of shadow-fleet oil tankers through the narrow and strategically vital Gulf of Finland. The message, according to Western officials, is that Russia is demonstrating both its capability and its willingness to operate aggressively in the region.
The Swedish navy’s growing concerns are echoed by its partners. Each nation bordering the Baltic faces its own vulnerabilities, but the shared threat from Russian hybrid tactics—combining conventional military force, cyber disruption, and covert operations—has led to an unprecedented level of coordination among NATO allies. As Petkovic and others have stressed, the need for vigilance is not likely to diminish anytime soon.
For Sweden, the stakes are particularly high. The country’s recent accession to NATO, following decades of military neutrality, has thrust it into the front lines of the alliance’s eastern flank. Swedish officials are acutely aware that their waters are now a critical buffer between Russia and the rest of northern Europe. The navy’s call for continued growth and modernization is as much about deterrence as it is about defense.
Still, the situation remains fluid. As the war in Ukraine drags on, the prospect of a ceasefire raises as many questions as it answers. Will Russia shift its focus to the Baltic, as Swedish intelligence predicts? Can NATO’s increased presence and cooperation deter further escalation? And what new forms might hybrid threats take as technology advances and old tactics evolve?
For now, the only certainty is uncertainty. The Baltic Sea, once again, is a stage for great power rivalry—its depths concealing not just submarines, but the future shape of European security. The Swedish navy, along with its NATO partners, is determined not to be caught off guard.
As the geopolitical currents shift, the vigilance of those who patrol the Baltic’s cold waters will remain a crucial line of defense—one that, for the time being, shows no sign of letting up.