“Irregular warfare enhances posture and options to counter an adversary’s gray zone activities and their counterintervention strategies”
–Senate Armed Services Committee testimony of former Assistant Secretary of Defense Christopher Maier and GEN (R) Bryan Fenton, 10 April 2024
Galvanized by Russia’s war of conquest in Ukraine, the two historically neutral Nordic states of Finland and Sweden applied for and were subsequently accepted into the North Atlantic Treaty Organization (NATO). This sea change brought with it a growth of 15 million people, and (with Finland’s accession alone) an additional 830 miles of Russia-NATO border, doubling NATO’s contiguous land border with Russia to 1,584 miles. This turn of events has been a challenge even for Moscow’s well-honed propaganda and political ‘spin’ machine—nothing about this growth was a strategic benefit for Russia. Referring to the 3.5 million men and women in uniform across the Atlantic—the combined might of the Alliance on NATO’s 75th anniversary—former NATO Secretary General Jens Stoltenberg said that the Alliance is “bigger, stronger and more united than ever.” While the addition of Finland and Sweden is clearly a windfall for the transatlantic alliance, their accession also means an increase in irregular warfare (IW) opportunities in both offensive and defensive toolkits.
Finland and Sweden’s accession into NATO present new IW opportunities because they are already two highly capable militaries. As the former Commander of United States European Command (USEUCOM) and Supreme Headquarters Allied Powers Europe (SHAPE), General Christopher Cavoli told congress, both Finland and Sweden bolstered the “collective defense capabilities” of NATO “from Day 1” of their entry into the Alliance. But more specifically, as Jonathan Schroden notes regarding the new Department of Defense Instruction (DODI) on Irregular Warfare—DODI 3000.07, published September 29, 2025—irregular warfare has both a reactive component (that of countering activities that threaten U.S. interests) and a proactive component. Proactively, irregular warfare can be used “to create dilemmas, deny access, or subvert an adversary’s capability and capacity to engage in aggressive or coercive behaviors.” The newest Nordic allies do just that—they provide opportunities for NATO given their existing capabilities, cultures, and geographic locations. These new IW opportunities can be considered in two categories: those that proactively bolster defensive capabilities, and those that create offensive or counter-offensive capabilities.
Strengthening Collective Defense
Firstly, both Nordic nations strengthen the net societal resilience of the Alliance. In fact, the Finnish people themselves are one of the potential asymmetric capabilities that Helsinki brings to the table. While the Finns only have between 22,000–24,000 active-duty personnel, the defense forces can mobilize an additional 280,000 reservists, and muster 870,000 fully trained citizens—which is a significant ratio of over 1 million trained personnel out of a total population of 5.6 million. As we have seen since the early stages of the war in Ukraine, even civilians with only rudimentary preparation can serve in the underground or auxiliary of a resistance network. In this way, Finland’s capacity to force-generate is an asymmetric capability that they have brought to the Alliance.
The Helsinki-based Hybrid Center of Excellence (Hybrid COE), while autonomous, provides unique value as well. Given its mandate to build the capabilities of its participating states to prevent and counter hybrid threats, the Hybrid COE is very much in the right place, at the right time. The Hybrid COE prides itself on “leading the conversation” on hybrid threats as it integrates professionals from the private sector and academia, and from across the European Union (EU) and NATO. Given the scope and scale of Russian-backed sabotage and other hybrid threats, the proven, pre-NATO analytical horsepower of the Hybrid COE makes it an asset.
Sweden also has a niche contribution to the Alliance in the realm of societal resilience and mobilizing the larger population against a threat. As highlighted in the Resistance Operating Concept, Sweden has already adopted the appropriate mindset to support the Total Defence model. Stockholm distributes a copy ofIn Case of Crisis or War to every household, a brochure that covers everything from basic first aid to emergency preparedness to countering misinformation. Updated in November 2024, In Case of Crisis reminds the population that during crisis or war, “we all need to contribute to Sweden’s resilience,” emphasizing that “If Sweden is attacked, we will never surrender. Any suggestion to the contrary is false.”
Similar to Finland, Sweden’s standing military is a relatively small one at about 24,000 personnel. However, NATO’s newest member offers a boutique counter-sabotage asset to the northern flank. For instance, Stockholm’s small submarine fleet brings a unique capability—and potentially an asymmetric advantage—to NATO. With four (three Gotland-class vessels and one Södermanland-class diesel-electric) submarines in service and two more on the way, Sweden is better postured to prevent Russian sabotage as their submarines are designed to operate in the shallow Baltic Sea, vice bulkier NATO vessels which are meant to operate elsewhere in deeper waters.
Perhaps even more important than its military, however, is Sweden’s technologically advanced defense industrial base. As RAND points out, Sweden is home to Saab as well as a subsidiary of the United Kingdom’s BAE systems, and with the production of the Gripen fighter jet, Archer artillery system, and CV-90 infantry fighting vehicle, Sweden has a “disproportionately large and sophisticated defence industry.” Ukraine’s recent progress towards the acquisition of Gripen E-model fighters exemplifies how Sweden’s Defense Industrial Base (DIB) can have a direct impact on European defense. While a long-term path towards equipping Ukraine was announced at a Saab factory in October 2025, Ukrainian President Volodymyr Zelenskyy also alluded to near-term deliveries for as early as 2026. The Gripen appealed to Kyiv as the small but agile fighter is built with a sophisticated electronic warfare (EW) suite that can enable the dispersed operating concept already adopted by the Ukrainian Air Force. Sweden’s mature and robust DIB produces both hardware and software, and straddles both offensive and defensive camps.
Opportunities Born of Capability and Proximity
In addition to their conventional force, Finland retains a highly capable special operations forces (SOF) formation, the Utti jaeger regiment, components of which have some of the same core activities as United States Special Operations Command (USSOCOM): special reconnaissance, unconventional warfare, and direct action. The winter warfare capabilities of Finnish SOF (FINSOF) might be the most critical tool that they bring to the Alliance, with U.S. forces already receiving mentorship from their new allies during combined training events focused on harsh winter combat.
But more tangibly, both Finland and Sweden’s respective territories give credence to the maxim that geography is destiny. As the Swedish government points out, Sweden’s geostrategic position plays a vital role in enabling the reinforcement of Europe from North America. Similarly, the Swedish Armed Forces have highlighted the importance of Gotland island, which enables the control of key supply routes between Finland and the Baltics. In addition to their geographic location, Finland and Sweden’s proximity to Russia are key drivers that enable potential operational dilemmas.
Finland’s frontline role provides a unique advantage for the Nordic countries in NATO. It offers geostrategic access for the Alliance to defend both the Baltic Sea and the Gulf of Bothnia, as well as bringing the Alliance closer to critical Russian strongholds in St. Petersburg and the Kola Peninsula. Now, with the Nordic states united in NATO, the Alliance has an opportunity to make its northern flank a lynchpin of its defense and deterrence from further Russian aggression. For instance, not only did the accession of Finland bring NATO to Russia’s northern doorstep, the 833-mile (1,340 km) shared border runs through mostly rural and forested areas, which opens the aperture regarding physical access. What was once a neutral space is now a potential threat vector for Russia, or at a minimum another front to defend or police.
Finland’s NATO membership in particular leaves Russian assets in Murmansk and the Barents Sea vulnerable, an advantage heretofore unavailable for the Alliance. As one analyst points out, Russia requires Murmansk and the Kola peninsula to sustain operations in the North Atlantic, and their loss would be a setback for Russia’s strategic deterrence in the region. In addition, whereas St. Petersburg has historically been in close proximity to only one NATO ally, Russia’s second-largest city is now only 93-miles (150 kilometers) from both Estonia and Finland. In the event of Russian aggression in the Baltics—a scenario famously war-gamed by RAND in 2016 with dispiriting results—any Russian gains would create only a salient into NATO territory, not a favorable position.
Proximity also serves to strengthen deterrence as it naturally makes deterrent threats more credible. Improved proximity lends credibility to Flexible Deterrent Options (FDOs) that are intended to be both on-order, and scalable. Similarly, Flexible Deterrent Options and Flexible Response Options do not just have to involve large formations, they can include SOF and focus on irregular warfare mission sets. The Alliance does not necessarily need large formations, or fifth-generation aircraft to create dilemmas by threatening things of value; it may in fact be less escalatory to use special operations forces to demonstrate capabilities in the High North to message these dilemmas to Moscow.
The benefit of proximity is compounded with improvements in NATO posture (generally framed as forces, footprints, and agreements) in the High North. In a historic move, Finland committed to hosting forward-stationed NATO troops within its borders at Rovaniemi and Sodankylä, and Finnish parliament approved a Defense Cooperation Agreement authorizing US forces to access and use 15 Finnish bases for both supplies and personnel.
Creating Dilemmas
The accession of Finland and Sweden is itself a dilemma for Putin. After Moscow’s invasion stalled, Norwegian and Estonian security services reported that Russian forces were reallocated from the High North to Ukraine, reducing the forces bordering Finland on the Kola Peninsula to a fifth of their pre-invasion numbers. However, before Finland and Sweden’s NATO accession approvals were even announced, Putin took a bellicose tone and pledged to return troops to the High North. Recent commercial imagery indicates new Russian military infrastructure such as storage facilities are in fact being built near the Finnish border. Moscow, however, is far from “set” in the region, and for now, NATO appears to have the posture advantage in Northern Europe.
Invoking Frederick the Great, it is useful to recall that he who “defends everything, defends nothing,” and stretching Russian military posture could actually be viewed as an advantage. Moves and counter-moves, reallocating forces and equipment, all expend resources. As a reaction to NATO’s northern growth, Russia has adjusted not just its own posture, but its own organization, splitting the Western Military District into Moscow and Leningrad districts “against NATO” amid the “backdrop of the entry into NATO of Finland and…Sweden.” Importantly, the simple fact remains that resources committed along the long Finnish border cannot be used in the Black Sea region or in the other Baltic States.
While there are clear advantages to being able to create operational dilemmas, there is the risk of an inadvertent security dilemma. NATO remains a defensive alliance, and measures taken to improve allied capabilities—activities ranging from planning, to exercising capabilities, to developing new footprints—are all done in the spirit of defense. Moscow, however, may interpret (or claim) any Finnish and Swedish actions as offensively minded, or done with hostile intent. Given the potential for the classic security dilemma, messaging is paramount, so demonstrations of capability are not mistaken for saber rattling.
Conclusion
While the February 2022 full-scale Russian invasion of Ukraine is the proximate cause of Finland and Sweden becoming the 31st and 32nd members of NATO, former Secretary Stoltenberg pointed to 2014 and the annexation of Crimea as a turning point for the Alliance, noting that since then, NATO has “undertaken the biggest reinforcement of our collective defence in generations.”
How can NATO best play this hand, and leverage its un-forecasted growth in a way that strengthens the Alliance, but does not escalate tensions? Leveraging the irregular warfare opportunities that come with the accession of Finland and Sweden provides one option. The capabilities, proximity, and posture opportunities open doors that had either been closed (or that the Alliance was reticent to knock on let alone open) for fear of escalation. Russia’s full-scale invasion of—and ongoing aggression against—Ukraine has changed the calculus.
Moscow has certainly learned a hard lesson about strategic context and unintended consequences, having violated the Clausewitzian admonition that the statesman and commander must know the kind of the war he is about to enter. Now, Russia has two highly capable Western powers bound by Article V of the Atlantic Charter on their doorstop—not two neutral parties—and the irregular warfare opportunities extend as far as the imagination of Allied planners.
Rick Chersicla is a 2025 non-resident fellow with the Irregular Warfare Initiative (IWI) and is affiliated with IWI-Europe.
Main Image: U.S. Navy Hospital Corpsman 1st Class Kepono Gowan launches an RQ-20 Puma unmanned aircraft system during Operation Baltic Sentry in Southern Finland, Feb. 24, 2025. Photo by LCpl Brian Bolin Jr., U.S. Marine Corps Forces, Europe and Africa. Public domain.
The views expressed in this article are those of the author and do not reflect the official positions of the United States Army, the Department of Defense, the Irregular Warfare Initiative, Princeton University’s Empirical Studies of Conflict Project, the Modern War Institute at West Point, or the United States Government.
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