Swedish Navy Reports “Weekly” Encounters With Russian Submarines in the Baltic Sea

The Swedish Navy has reported an alarming rise in encounters with Russian submarines in the Baltic Sea, describing such incidents as occurring “almost weekly.” According to Capt. Marko Petkovic, Chief of Operations, Moscow has been “continuously reinforcing” its naval presence in the region, with sightings of Russian vessels now a routine part of Sweden’s maritime surveillance operations. He noted that the frequency of these encounters has grown steadily in recent years.

The Baltic Sea has increasingly become a hotspot for geopolitical tensions, with threats ranging from suspected hybrid operations using drones to alleged sabotage of underwater infrastructure. Adding to the volatility is Russia’s so-called “shadow fleet” — ageing, civilian-flagged oil tankers transporting crude oil — which regional officials fear could be repurposed for military use, including drone-launch capabilities.

The UK recently highlighted its own concerns after a Russian intelligence vessel reportedly entered British waters and used laser equipment against military pilots, a move the British defence secretary described as part of a “new era of threat.”

Against this backdrop, Sweden recently hosted Playbook Merlin 25, a major NATO anti-submarine warfare exercise involving nine nations, including Germany, France, and the United States. Hundreds of personnel took part in submarine-hunting drills designed to prepare for underwater threats in the Baltic’s complex seabed terrain. The region’s hilly underwater topography makes detecting submarines particularly difficult, allowing them to evade surveillance.

Petkovic warned that Russia is steadily expanding its submarine capabilities, producing approximately one Kilo-class submarine per year in St. Petersburg and the Kaliningrad enclave. He described this as part of a “deliberate and constant modernisation programme.”

He further cautioned that any future ceasefire or armistice in the Ukraine war may free up Russian military assets and increase Moscow’s focus on the Baltic region. “The Swedish navy must continue to strengthen and maintain a broad operational perspective,” he said.

Underwater infrastructure also remains a major point of vulnerability. Variations in visibility, salinity and temperature make the Baltic Sea a challenging environment for surveillance, raising risks to critical infrastructure such as communication cables and energy pipelines. Petkovic emphasised that countries including Sweden, Norway, Finland, Estonia and Lithuania are “fully dependent” on secure maritime communication lines for societal and economic stability.

Nevertheless, he expressed confidence that enhanced NATO coordination is making a difference. Since the launch of Operation Baltic Sentry in January, no new cable incidents have been reported. Petkovic said this demonstrates the effectiveness of allied cooperation and heightened awareness among commercial vessels navigating the region.

“Whether past incidents were state-sponsored or the result of poor seamanship, the increased vigilance has clearly raised awareness,” he added. “The alliance is unified, and we are closing ranks against emerging threats.”