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NATO Allies are conducting anti-submarine warfare exercise Playbook Merlin 25 in the Baltic Sea from November 10 to 14, 2025. The exercise brings together submarines, ships, and aircraft from nine allied nations.

Hosted by Sweden and directed by NATO’s Allied Maritime Command (MARCOM), the exercise aims to enhance readiness, interoperability, and the ability to detect and counter underwater threats in one of Europe’s most strategically vital regions.

Participating forces include submarines from Germany and Sweden, Maritime Patrol Aircraft from the United States, and surface ships and helicopters from France, Germany, the Netherlands, and Sweden. The coordinated operations in the confined and busy waters of the Baltic Sea test NATO’s ability to respond quickly and efficiently to evolving maritime challenges.

Rear Adm. Bret Grabbe, Commander NATO Submarines, highlighted the significance of Sweden’s leadership in the exercise, stating. “Sweden plays an integral role in maritime security in the Baltic Sea,” he said.

Grabbe added that, “the Baltic nations bring an impressive array of ASW capabilities to NATO, as well as experienced leadership and maritime capacity. We thank the Swedish Navy for hosting exercise Merlin as well as all NATO navies that are participating and sharing regional ASW expertise.”

NATO’s newest member Sweden hosts Playbook #Merlin25. Allied 🇩🇪🇸🇪 submarines, ships & aircraft joined forces for this major NATO anti-submarine warfare exercise in the #BalticSea 🌊Hosted by Sweden and led by #NATO MARCOM, the exercise strengthened Allied readiness,… pic.twitter.com/bZa4zL9Yvu

— NATO Maritime Command (@NATO_MARCOM) November 12, 2025

The exercise reflects NATO’s operational flexibility and commitment to protecting critical sea lanes, energy infrastructure, and communication networks in the Baltic region.

Sweden’s Role in NATO

For Sweden, Playbook Merlin 25 marks an important demonstration of its contribution to NATO as its newest member. Rear Admiral Johan Norlen, Chief of the Swedish Navy, emphasized Sweden’s readiness to shoulder greater responsibilities within the Alliance. “As the newest member of NATO, the Swedish Navy is proud to host Playbook activity Merlin once again.”

He added that “by sharing our knowledge and experience of underwater warfare in the unique conditions of the Baltic Sea region, we increase the security and stability, make NATO stronger and address the security challenges of today.”

“It also demonstrates that Sweden is a NATO member that can be trusted and expected to take a big responsibility within the alliance, now and in the future,” Norlen added.

NATO officials describe Sweden’s participation as critical for collective defense, noting that the Baltic’s shallow waters, dense traffic, and variable acoustic conditions make it a uniquely demanding environment for anti-submarine operations.

Cross Domain Integration

On 12 November, as Playbook Merlin 25 continued at sea, a U.S. Air Force B-52H Stratofortress from Moron Air Base in Spain conducted strategic flights over Northern Europe, coinciding with the exercise.

The synchronized operations underscore NATO’s multi-domain deterrence posture, integrating air and maritime elements to safeguard Europe’s northern and eastern frontiers.

According to U.S. Air Forces in Europe, B-52 aircraft from the 2nd Bomb Wing arrived in Spain on 8 November for Bomber Task Force Europe 26-1, designed to enhance coordination with Allied air forces and rehearse long-range strike profiles.

Flight tracking data showed the bombers operating over the Baltic Sea and along Russia’s northwestern borders, an illustration of NATO’s ability to project power and monitor key maritime corridors.

At sea, Merlin 25 crews are conducting complex ASW maneuvers with advanced sonars, dipping-sonar helicopters, and P-8-class patrol aircraft to locate and track diesel-electric submarines. Together, these operations demonstrate the layered deterrence strategy NATO employs, linking air, sea, and undersea capabilities to maintain control and transparency in contested environments.

Operational and Strategic Significance

The interplay between bomber flights and naval drills is deliberate, designed to practice integrated deterrence rather than provocation. The exercises display NATO’s capacity to surveil, cue, and, if necessary, engage across multiple domains and distances.

The combination of long-range airpower and littoral anti-submarine assets also highlights how Allied modernization and coordination sustain deterrence credibility. The B-52, in service since the 1950s but continually upgraded, symbolizes endurance and adaptability. Similarly, the Baltic navies’ air-independent propulsion submarines and networked surface combatants represent a modern, data-driven approach to undersea defense.

Geopolitically, the exercise signals NATO’s resolve to protect the Baltic Sea, an artery for European commerce and security. It also addresses vulnerabilities exposed by recent incidents involving seabed infrastructure and undersea cables.

NATO’s Broader Maritime Training Framework

Playbook Merlin 25 is one of nearly a dozen major maritime exercises organized annually by NATO Allied Maritime Command, alongside Dynamic Mongoose in the North Atlantic and Dynamic Manta in the Mediterranean. Together, these drills form a comprehensive training architecture designed to keep NATO ready, united, and capable, above and below the waves.

Standing NATO Maritime Groups continue to provide a constant presence under MARCOM’s operational control, ensuring coordinated maritime security across the Alliance. Through exercises like Merlin 25, NATO reinforces the message that credible defense comes from integration, cooperation, and continual readiness.