Sweden shadows Russian Kilo-class submarine in Baltic amid NATO reinforced naval vigilance.

A Russian Project 636.3 Kilo-class submarine entered the Baltic Sea on October 15, tracked by Swedish Gripen fighters and Visby-class corvettes. The escort marks another NATO-coordinated operation as the alliance monitors unusual Russian naval movements across European waters.

The Swedish Navy announced on October 15, 2025, that a Russian submarine transited into the Baltic Sea via the Great Belt and was met in the Kattegat by Swedish fighter aircraft and naval vessels, which continue to shadow its movement in coordination with allied forces. The operation follows days of alliance monitoring after the same submarine was photographed operating on the surface off Brittany, and later escorted through the North Sea, a pattern that raised questions about its condition. The boat is consistent with Russia’s Project 636.3 Kilo class, a diesel electric design armed with 533 mm torpedoes and Kalibr cruise missiles, optimized for quiet coastal warfare.
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Swedish Navy corvettes and JAS 39 Gripen fighters shadow a surfaced Russian Project 636.3 Kilo-class submarine transiting the Baltic Sea, in a NATO-coordinated operation underscoring heightened vigilance over Russian naval movements (Picture source: Swedish Navy)

Sweden’s intercept package combines its frontline JAS 39 Gripen fighters with corvettes from the Visby class, a pairing tailored to the shallow, cluttered waters of the Baltic approaches. Gripen C/D carries the PS 05/A Mk 4 radar and data links for beyond visual range control of Meteor air to air missiles, giving Swedish pilots the sensor reach and endurance to maintain a persistent combat air patrol over maritime intercepts. The type’s short turnaround and dispersed basing are particularly valuable when a contact must be held continuously over several straits and sea lanes.

At sea, Visby class corvettes are built for stealth with composite hulls and low signatures, the 650 ton ships sprint at 35 knots, then slow to hunt using sonar and fire control linked to Saab lightweight torpedoes in the Torped 45 and newer Torped 47 family. For surface deterrence they carry the 57 mm Bofors gun and RBS 15 anti ship missiles, a loadout that allows the same hull to chase a periscope one hour and to cover a choke point the next. In practice, a Visby on the contact track is the bridge between air finds and subsurface fixes.

The Russian submarine’s decision to travel surfaced through busy waters has two credible explanations. Moscow says it complied with navigation rules in congested channels, an argument that is not unusual for diesel electric boats passing the English Channel. NATO officials, however, noted the submarine remained on the surface for much of the voyage and at times under tow, behavior more consistent with propulsion or fuel system trouble. Either way, a surfaced Kilo is stripped of its comparative advantage, silence, and becomes a hull to be escorted rather than a threat to be hunted.

In Russian service the Project 636.3 Kilo, exemplified by the Novorossiysk, is a proven ambusher. The class displaces roughly 3,000 tons submerged, carries six 533 mm tubes for torpedoes or mines, and can launch Kalibr land attack and anti ship missiles from its fire control suite. Designed to run on batteries for quiet sprint and drift tactics in littoral zones, it can linger in choke points to threaten undersea cables, shipping lanes, or naval task groups. Those attributes explain both NATO’s interest and Sweden’s choice to meet it with sensors above and below the surface.

The Swedish Armed Forces described the shadowing as a routine mission conducted with allies, a phrase that now carries literal treaty weight. Sweden became NATO’s thirty second member on March 7, 2024, and has since integrated its air and maritime picture with alliance nodes from the Danish Straits to Poland’s coast. NATO’s maritime arm signaled the same vigilance days earlier by publicizing the surfaced Russian boat off France. In this environment, every escorted transit doubles as a readiness drill. It also telegraphs to Moscow that Baltic movements are mapped, tagged, and, when necessary, bracketed by Swedish and allied platforms.