NATO Collective Legal Interpretations: Strengthening Alliance Deterrence and Protecting Baltic Undersea Assets Against Grey-Zone Threats
The MOC
By
Catherine Marie Abbott
May 26, 2026
The Baltic Maritime Security Context
Emerging as a coercive tool used to circumvent international energy sanctions after the onset of the Ukrainian-Russo War in 2022, Russian shadow vessels have since become a means of asymmetric tactics, challenging NATO states’ resolve and collective response. As part of Russia’s broader maritime posture, shadow vessels are an array of aging oil and auxiliary tankers operating under opaque and decentralized ownership structures, using shell corporations, flag of convenience (FOC), and opportunistic flag registrations to transport sanctioned energy. These state-affiliated vessels have been notoriously associated with damage to critical undersea infrastructure (CUI), most notably within the Baltic Sea domain.
The Baltic Sea, a central component of the European security apparatus, operates as a heavily fortified arena, insulated by NATO allies following the accession of Finland and Sweden. Baltic CUI enables digital synergy among regional actors, enhancing energy and economic security. Disruptions to these subsea assets would have aggregate effects, as NATO and EU communications and operational resilience are heavily reliant on subsea data transmission. Accordingly, Article 3 of the North Atlantic Treaty establishes the foundation for collective resilience, empowering members to maintain and develop collective capacity and interoperability to resist armed adversarial attacks. While traditionally associated with conventional defense and operational readiness, its relevance extends to the protection of critical societal functions, including energy, transport, and communications systems, sustaining alliance resilience in grey-zone threat landscapes.
Acting as the primary legal framework governing state authority in the maritime domain, the United Nations Convention on the Law of the Sea (UNCLOS), designed for the binary distinction between conflict and peacetime, was not sufficiently fashioned for a hybrid threat landscape. Differing ratification statuses, selective adherence to UNCLOS provisions, uneven enforcement capabilities, and obfuscating tactics employed by shadow vessels has caused state-level fragmentation in legal interpretation. As a result, responsiveness toward asymmetric threat vectors has been exacerbated. This inherent fragmentation has produced significant systemic strategic and reputational challenges for the alliance, founded on collective response and operating within a rules-based international order. Notably, this fragmented and uneven maritime enforcement environment under hybrid conditions constrains cohesive alliance responsiveness and contributes to vulnerabilities in the protection and deterrence of subsea infrastructure.
Asymmetric Maritime Interpretations and Enforcement
Established under NATO’s coordinated framework, the Allied Maritime Command (MARCOM) facilitates joint naval operations and acts as the alliance’s primary advisor on maritime issues, utilizing relevant UNCLOS provisions, including freedom of navigation and innocent passage in territorial seas and exclusive economic zones (EEZs). Despite operating under a unified force structure, NATO does not enforce a harmonized interpretation of UNCLOS nor override national legal doctrines; instead, member states maintain sovereign authority over legal interpretation and application in accordance with domestic legal frameworks. Although empowering state sovereignty, this has deferred enforcement responsibilities of shadow vessels to individual member states regardless of naval capability, yielding uneven enforcement outcomes across the alliance and structural vulnerabilities regarding the protection and deterrence of CUI.
For instance, in 2025, the Estonian Navy intercepted Jaguar, a suspected Russian-affiliated sanctioned shadow fleet vessel operating under the Gabon state flag; despite its effort, Estonia could not forcibly board the non-compliant vessel, citing its lack of naval capabilities as well as the threatening overarching presence of a Russian jet escorting the ship. In a similar incident, in April 2026, Russian frigate Admiral Grigorovich escorted sanctioned shadow vessels through the English Channel, an act described as a direct challenge to allied forces attempting interception.
Under UNCLOS, states must preserve freedom of movement on the high seas, with authorized jurisdiction delegated to a vessel’s flag-state, requiring a genuine link between vessel and state. Foreign-flagged ships cannot obstruct a vessel’s voyage unless under circumstances of piracy and statelessness, though articles do not expressly define what constitutes statelessness, i.e., fraudulent registration versus no registration. Notably, not all NATO members have ratified UNCLOS, with the U.S. and Türkiye remaining non-signatory states, selectively regarding the convention’s provisions as customary international law, in contrast to their NATO counterparts maintaining strict adherence to the convention as a legally binding framework
Given its non-party status, the United States generally applies an extensive domestic legal framework, including United States v. Marino Garcia (1982) and 14 U.S.C. § 522, classifying vessels operating under false flags, lacking authentic registration, or possessing multiple registrations as stateless and subject to U.S. jurisdiction, thereby lowering evidentiary thresholds and permitting escalation from UNCLOS-compliant right-of-visit procedures to full maritime interdiction once statelessness is determined. Though UNCLOS is structured around exclusive flag-state jurisdiction and does not authorize unilateral interdiction of foreign-flagged vessels on the high seas. These legal authorities, coupled with the United States’ unparalleled naval capabilities and blue-water operational experience, enabled the 2026 seizure of Marinera and subsequent seizures involving M/T Skipper, M/T Sophia, Olina, and Sagitta.
Conversely, European NATO states strictly adhering to convention provisions have largely adopted a cautious, legitimacy-based approach toward Russian-affiliated vessels, favoring active surveillance initiatives such as Baltic Sentry for data acquisition and information sharing, as well as deterrence by presence to safeguard Baltic subsea infrastructure. Despite enhancing surveillance initiatives and intelligence dissemination among NATO members, Baltic Sea states have contended with shadow vessels exploiting FOC, rapid mid-voyage reflagging, fraudulent certifications, AIS manipulation, and opaque ownership structures to obscure flag-state jurisdiction while maintaining nominally compliant documentation, obfuscating required evidentiary thresholds required for UNCLOS-compliant interdiction and stateless designation.
However, in 2026, following the seizure of Marinera, various UNCLOS-compliant NATO members issued a Joint Statement indicating ships misusing tracking data, transiting without valid documentation, or conducting ship-to-ship transfers can be observed as stateless. Despite intensified kinetic engagement by European NATO states, many seized vessels, including Grinch, have been released following multi-million-euro fines and continue to engage in shadow fleet activities, primarily due to high logistical costs of detention and the absence of a clear legal framework for permanent seizure across many jurisdictions. Or in 2025, in the case of Vezhen, prosecutors could not definitively prove in court that the vessel, suspected of sabotaging subsea communication cables connecting Sweden and Latvia, had malicious intentions and was since released into the maritime ecosystem.
Geostrategic and Operational Implications
The general disjointedness in legal interpretations and uneven and unsustainable enforcement capabilities among NATO member states has eroded the alliance’s strategic and reputational objectives in the international domain, incentivizing hybrid escalatory tactics by adversarial actors and increasing the likelihood of Baltic CUI damage, maritime volatility, and kinetic confrontation. Firstly, parallel tensions in the Strait of Hormuz alongside growing domestic dissatisfaction within the United States regarding NATO burden-shari
U.S. President Donald Trump’s gunboat diplomacy and aggressive interdiction strategy reinforces the archetype that European NATO states function as free riders within the alliance apparatus. Similarly, the 2025 introduction of legislation from Representative Thomas Massie, H.R. 5608, the NATO Act, proposing withdrawal from the military alliance due to financial expenditures and perceived lack of allied burden-sharing, alongside 2026 remarks from U.S. Secretary of State Marco Rubio indicating that the U.S. may reexamine its commitment to the alliance due to limitations imposed by European allies regarding military installation access during ongoing the Israel–U.S.–Iran conflict. This, alongside recent policy adjustments, including the temporary easing and delisting of sanctions
Notably, Russia, attempting to redefine the balance of power in the Baltic Sea and the Finnish Gulf, has adopted a revisionist posture, via its illicit alteration of its baseline under Resolution 918 and intensifying military escort operations of shadow vessels through NATO states’ area of responsibility. These measures have hindered, though not completely halted, allied interdiction strategies, yet many pundits have noted Europe’s inherent trepidation of a Russian counter-response and instead will impose a self-restrained response to shadow vessels.
Additionally, European NATO members’ strict observation of UNCLOS provisions, including limited interdiction authority within the EEZ and permissiveness toward sub-Article-5-threshold activity, has increased maritime volatility, enabling additional adversaries, namely China, to escalate destructive irregular activities against Baltic CUI through vessels such as Newnew Polar Bear (2023) and Yi Peng 3 (2024), and Russia’s subsea CUI mapping. Strategically, these incidents signal that UNCLOS-compliant NATO states may prioritize navigational legality and procedural legitimacy over responsive deterrence, contributing to prevailing perceptions of weakened enforcement credibility within the maritime domain. Simultaneously, the gradual recalibration from active surveillance to kinetic enforcement operations increases the likelihood of confrontation between NATO and Russia through strategic miscalculation as European NATO states attempt to restore deterrence and reputational credibility.
Policy Recommendations
To reestablish cohesiveness and optimize collective response while respecting international maritime law and differing signatory statuses, NATO member states should establish a harmonized interpretive baseline for UNCLOS to enable timely and seamless responses that secure critical infrastructure from irregular maritime threats. Within this framework, the North Atlantic Council would operate as the principal decision-making body for coordinating legal interpretation among allied states. Operationally and strategically, alliance-wide harmonization would improve consistency in responses to asymmetric maritime threats and reduce reliance on unilateral legal interpretations.
Given UNCLOS’s current limitations, NATO should develop an internal supplementary protocol under MARCOM to address legal and operational gaps in grey-zone maritime activity. Under the principle of lex specialis, NATO’s treaty-based framework may serve as a specialized mechanism for alliance coordination without modifying the rights of non-members or contradicting core UNCLOS provisions. Long-term, NATO member states should pursue externalization of these practices through United Nations-led process, enabling consideration of a supplementary protocol addressing hybrid maritime activity and subsea infrastructure protection for maritime law.
To address uneven enforcement capabilities among allied states, NATO should establish a coordinated burden-sharing framework governed by graduated legal thresholds tied to evidentiary certainty and jurisdictional clarity. Under this structure, MARCOM would function as a legal-validation and coordination node integrating intelligence dissemination, and allied reporting to support shared determinations about suspicious maritime activity. Lower-certainty scenarios would correspond to surveillance and monitoring. Validated statelessness or confirmed subsea sabotage would permit coercive responses, including diversion or interdiction, under national legal authorities. Collectively, this framework would reduce operational miscalculations while satisfying high evidentiary support standards required for legal enforcement authorities.
Conclusion
Although UNCLOS was not adequately fabricated for irregular activities, NATO’s ability to ultimately address hybrid threat vectors solely relies on its political willingness. If adversaries suspect fissures within the alliance’s force structure, hybrid activities will escalate with grievous repercussions. Although NATO, particularly European member states, operates within a rules-based international order, allied governments must remain cognizant that adversarial states, most notably Russia, are increasingly willing to employ coercive and asymmetric maritime measures for strategic and geopolitical gain, despite being signatories to UNCLOS. Simultaneously, the United States must recognize that maintaining maritime order and alliance credibility requires operating in tandem with its European counterparts as a cohesive and perceivable hegemonic bloc, as the durability of U.S. strategic influence and the preservation of the state system’s rules-based order remain inherently connected to allied interoperability and joint deterrence.
Catherine Marie Abbott holds a master’s in security policy studies at George Washington University Elliott School of International Affairs, specializing in maritime security and intelligence analysis. Her research primarily focuses on maritime logistics, emerging technology, and intelligence processing.
The views expressed in this piece are the sole opinions of the author and do not necessarily reflect those of the Center for Maritime Strategy or other institutions listed.
Center for Maritime Strategy
By Catherine Marie Abbott
The Baltic Maritime Security Context
Emerging as a coercive tool used to circumvent international energy sanctions after the onset of the Ukrainian-Russo War in 2022, Russian shadow vessels have since become a means of asymmetric tactics, challenging NATO states’ resolve and collective response. As part of Russia’s broader maritime posture, shadow vessels are an array of aging oil and auxiliary tankers operating under opaque and decentralized ownership structures, using shell corporations, flag of convenience (FOC), and opportunistic flag registrations to transport sanctioned energy. These state-affiliated vessels have been notoriously associated with damage to critical undersea infrastructure (CUI), most notably within the Baltic Sea domain.
The Baltic Sea, a central component of the European security apparatus, operates as a heavily fortified arena, insulated by NATO allies following the accession of Finland and Sweden. Baltic CUI enables digital synergy among regional actors, enhancing energy and economic security. Disruptions to these subsea assets would have aggregate effects, as NATO and EU communications and operational resilience are heavily reliant on subsea data transmission. Accordingly, Article 3 of the North Atlantic Treaty establishes the foundation for collective resilience, empowering members to maintain and develop collective capacity and interoperability to resist armed adversarial attacks. While traditionally associated with conventional defense and operational readiness, its relevance extends to the protection of critical societal functions, including energy, transport, and communications systems, sustaining alliance resilience in grey-zone threat landscapes.
Acting as the primary legal framework governing state authority in the maritime domain, the United Nations Convention on the Law of the Sea (UNCLOS), designed for the binary distinction between conflict and peacetime, was not sufficiently fashioned for a hybrid threat landscape. Differing ratification statuses, selective adherence to UNCLOS provisions, uneven enforcement capabilities, and obfuscating tactics employed by shadow vessels has caused state-level fragmentation in legal interpretation. As a result, responsiveness toward asymmetric threat vectors has been exacerbated. This inherent fragmentation has produced significant systemic strategic and reputational challenges for the alliance, founded on collective response and operating within a rules-based international order. Notably, this fragmented and uneven maritime enforcement environment under hybrid conditions constrains cohesive alliance responsiveness and contributes to vulnerabilities in the protection and deterrence of subsea infrastructure.
Asymmetric Maritime Interpretations and Enforcement
Established under NATO’s coordinated framework, the Allied Maritime Command (MARCOM) facilitates joint naval operations and acts as the alliance’s primary advisor on maritime issues, utilizing relevant UNCLOS provisions, including freedom of navigation and innocent passage in territorial seas and exclusive economic zones (EEZs). Despite operating under a unified force structure, NATO does not enforce a harmonized interpretation of UNCLOS nor override national legal doctrines; instead, member states maintain sovereign authority over legal interpretation and application in accordance with domestic legal frameworks. Although empowering state sovereignty, this has deferred enforcement responsibilities of shadow vessels to individual member states regardless of naval capability, yielding uneven enforcement outcomes across the alliance and structural vulnerabilities regarding the protection and deterrence of CUI.
For instance, in 2025, the Estonian Navy intercepted Jaguar, a suspected Russian-affiliated sanctioned shadow fleet vessel operating under the Gabon state flag; despite its effort, Estonia could not forcibly board the non-compliant vessel, citing its lack of naval capabilities as well as the threatening overarching presence of a Russian jet escorting the ship. In a similar incident, in April 2026, Russian frigate Admiral Grigorovich escorted sanctioned shadow vessels through the English Channel, an act described as a direct challenge to allied forces attempting interception.
Under UNCLOS, states must preserve freedom of movement on the high seas, with authorized jurisdiction delegated to a vessel’s flag-state, requiring a genuine link between vessel and state. Foreign-flagged ships cannot obstruct a vessel’s voyage unless under circumstances of piracy and statelessness, though articles do not expressly define what constitutes statelessness, i.e., fraudulent registration versus no registration. Notably, not all NATO members have ratified UNCLOS, with the U.S. and Türkiye remaining non-signatory states, selectively regarding the convention’s provisions as customary international law, in contrast to their NATO counterparts maintaining strict adherence to the convention as a legally binding framework
Given its non-party status, the United States generally applies an extensive domestic legal framework, including United States v. Marino Garcia (1982) and 14 U.S.C. § 522, classifying vessels operating under false flags, lacking authentic registration, or possessing multiple registrations as stateless and subject to U.S. jurisdiction, thereby lowering evidentiary thresholds and permitting escalation from UNCLOS-compliant right-of-visit procedures to full maritime interdiction once statelessness is determined. Though UNCLOS is structured around exclusive flag-state jurisdiction and does not authorize unilateral interdiction of foreign-flagged vessels on the high seas. These legal authorities, coupled with the United States’ unparalleled naval capabilities and blue-water operational experience, enabled the 2026 seizure of Marinera and subsequent seizures involving M/T Skipper, M/T Sophia, Olina, and Sagitta.
Conversely, European NATO states strictly adhering to convention provisions have largely adopted a cautious, legitimacy-based approach toward Russian-affiliated vessels, favoring active surveillance initiatives such as Baltic Sentry for data acquisition and information sharing, as well as deterrence by presence to safeguard Baltic subsea infrastructure. Despite enhancing surveillance initiatives and intelligence dissemination among NATO members, Baltic Sea states have contended with shadow vessels exploiting FOC, rapid mid-voyage reflagging, fraudulent certifications, AIS manipulation, and opaque ownership structures to obscure flag-state jurisdiction while maintaining nominally compliant documentation, obfuscating required evidentiary thresholds required for UNCLOS-compliant interdiction and stateless designation.
However, in 2026, following the seizure of Marinera, various UNCLOS-compliant NATO members issued a Joint Statement indicating ships misusing tracking data, transiting without valid documentation, or conducting ship-to-ship transfers can be observed as stateless. Despite intensified kinetic engagement by European NATO states, many seized vessels, including Grinch, have been released following multi-million-euro fines and continue to engage in shadow fleet activities, primarily due to high logistical costs of detention and the absence of a clear legal framework for permanent seizure across many jurisdictions. Or in 2025, in the case of Vezhen, prosecutors could not definitively prove in court that the vessel, suspected of sabotaging subsea communication cables connecting Sweden and Latvia, had malicious intentions and was since released into the maritime ecosystem.
Geostrategic and Operational Implications
The general disjointedness in legal interpretations and uneven and unsustainable enforcement capabilities among NATO member states has eroded the alliance’s strategic and reputational objectives in the international domain, incentivizing hybrid escalatory tactics by adversarial actors and increasing the likelihood of Baltic CUI damage, maritime volatility, and kinetic confrontation. Firstly, parallel tensions in the Strait of Hormuz alongside growing domestic dissatisfaction within the United States regarding NATO burden-shari
U.S. President Donald Trump’s gunboat diplomacy and aggressive interdiction strategy reinforces the archetype that European NATO states function as free riders within the alliance apparatus. Similarly, the 2025 introduction of legislation from Representative Thomas Massie, H.R. 5608, the NATO Act, proposing withdrawal from the military alliance due to financial expenditures and perceived lack of allied burden-sharing, alongside 2026 remarks from U.S. Secretary of State Marco Rubio indicating that the U.S. may reexamine its commitment to the alliance due to limitations imposed by European allies regarding military installation access during ongoing the Israel–U.S.–Iran conflict. This, alongside recent policy adjustments, including the temporary easing and delisting of sanctions
Notably, Russia, attempting to redefine the balance of power in the Baltic Sea and the Finnish Gulf, has adopted a revisionist posture, via its illicit alteration of its baseline under Resolution 918 and intensifying military escort operations of shadow vessels through NATO states’ area of responsibility. These measures have hindered, though not completely halted, allied interdiction strategies, yet many pundits have noted Europe’s inherent trepidation of a Russian counter-response and instead will impose a self-restrained response to shadow vessels.
Additionally, European NATO members’ strict observation of UNCLOS provisions, including limited interdiction authority within the EEZ and permissiveness toward sub-Article-5-threshold activity, has increased maritime volatility, enabling additional adversaries, namely China, to escalate destructive irregular activities against Baltic CUI through vessels such as Newnew Polar Bear (2023) and Yi Peng 3 (2024), and Russia’s subsea CUI mapping. Strategically, these incidents signal that UNCLOS-compliant NATO states may prioritize navigational legality and procedural legitimacy over responsive deterrence, contributing to prevailing perceptions of weakened enforcement credibility within the maritime domain. Simultaneously, the gradual recalibration from active surveillance to kinetic enforcement operations increases the likelihood of confrontation between NATO and Russia through strategic miscalculation as European NATO states attempt to restore deterrence and reputational credibility.
Policy Recommendations
Conclusion
Although UNCLOS was not adequately fabricated for irregular activities, NATO’s ability to ultimately address hybrid threat vectors solely relies on its political willingness. If adversaries suspect fissures within the alliance’s force structure, hybrid activities will escalate with grievous repercussions. Although NATO, particularly European member states, operates within a rules-based international order, allied governments must remain cognizant that adversarial states, most notably Russia, are increasingly willing to employ coercive and asymmetric maritime measures for strategic and geopolitical gain, despite being signatories to UNCLOS. Simultaneously, the United States must recognize that maintaining maritime order and alliance credibility requires operating in tandem with its European counterparts as a cohesive and perceivable hegemonic bloc, as the durability of U.S. strategic influence and the preservation of the state system’s rules-based order remain inherently connected to allied interoperability and joint deterrence.
Catherine Marie Abbott holds a master’s in security policy studies at George Washington University Elliott School of International Affairs, specializing in maritime security and intelligence analysis. Her research primarily focuses on maritime logistics, emerging technology, and intelligence processing.
The views expressed in this piece are the sole opinions of the author and do not necessarily reflect those of the Center for Maritime Strategy or other institutions listed.