A threat with defence implications

The defence-related dimension of the shadow fleet is of central importance but has so far received insufficient attention. Acts of sabotage, at sea and on land, have become a central instrument of Russian activity in Europe. Numerous drone overflights across European territory also appear to correlate with shadow fleet vessel movements. As a result, the fleet expands the overall threat spectrum and becomes relevant to defence policy. It cannot be ruled out that acts of sabotage and espionage are employed as preparatory measures or in support of poten­tial military operations (the so-called shap­ing of the environment). Espionage and sabotage conducted via the shadow fleet may therefore provide the adversary with valuable information and operational insights, for example regarding procedural workflows and response times in the event of damage to critical maritime infrastructure.

One such case was the damage to the Estlink 2 subsea power cable in the Baltic Sea. The cable connects Finland and Estonia and was damaged on Christmas Day 2024 by the anchor of the tanker Eagle S. The vessel, which has been linked to Russia’s shadow fleet, dragged its anchor across the seabed and damaged four further subsea cables in addition to Estlink 2. During such significant holidays, it may be of additional interest to potential adversaries to observe response times and procedures in dealing with such incidents. Following its detention, the captain of the Eagle S was report­edly instructed via radio to destroy evidence of its activities in the form of charts depict­ing local subsea cables.

However, the threat is not limited to shadow fleet tankers, their anchors, and alleged accidents. Cargo ships, container vessels, and fishing boats may also pose security and defence-related risks. The deployment of drones or container-based weapons systems and electronic jamming systems is possible both in the lead-up to or during an armed conflict and enables the asymmetric use of such vessels, for example in a first-strike scenario at the outset of hostilities. Given the large number of ships in European waters, preparing for such con­tingencies is difficult. For potential adver­saries, low-threshold options are also con­ceivable, including deliberately induced maritime accidents in straits, canals such as the Kiel Canal, or key shipping routes such as the Elbe River as the access route to the Port of Hamburg.

Undermining of international law

Within the framework of the two core prin­ciples of the law of the sea, namely the free­dom of navigation (Article 87 of the United Nations Convention on the Law of the Sea) and the right of innocent passage (Article 17), shadow fleet vessels operate within allied and German territorial waters and exclusive economic zones (EEZs). In these areas, they may interfere with critical infra­structure or, in the event of conflict, project effects into vulnerable population centres. At the same time, Russia seeks to delegitimise potential Western countermeasures through allegations of piracy and to justify possible responses (“lawfare”). Consequently, this reveals not only an operational risk but also a broader strategic erosion of key norms underpinning the international order. The deliberate instrumentalisation of shipping activities in these maritime areas for non-peaceful purposes runs counter to these international agreements.

Environmental risks

Environmental threats must also be empha­sised. They arise from the advanced age and poor condition of the vessels, as well as from the working conditions of crews that spend extended periods at sea. The shadow fleet is regularly involved in accidents and maritime incidents, as illustrated by the case of the Eventin off the German coast, sinking oil tankers in the Black Sea, and multiple other examples in Europe and Asia. Fur­ther, potentially more severe accidents can­not be ruled out. Due to the almost enclosed geography of the Baltic Sea and its limited water exchange, a single tanker casualty in this region could severely impact the area for years or even decades, with far-reaching consequences for the marine environment, the economy, and tourism.

Military deterrence

In addition, Russia is increasingly employing military capabilities to protect shadow fleet vessels and its export system, thereby deterring Western interventions. The at­tempted interception of the tanker Jaguar by Estonian authorities in May 2025 on the grounds of false flag registration illustrates this dynamic. When Russia deployed an Su-35 fighter jet to overfly the vessel – alleg­edly associated with the shadow fleet – Estonian authorities, which had dispatched a patrol boat and a helicopter, abandoned their attempt. The tanker was then able to reach its destination unimpeded.

Apparently, Russia is succeeding in de­terring Germany and many of its partners from adopting clearer and more robust measures against the shadow fleet by threatening military escalation. As a result, Moscow continues to rely on both rhetorical and military displays of intimidation. The Federal Republic and its partners are squandering the available room for ma­noeuvre below the threshold of armed conflict through inconsistent responses, protracted debates, jurisdictional and legal disputes, and self-deterrence driven by fears of military escalation. This behaviour is what enables Russia to deliberately exploit the grey zone, ranging from the shadow fleet to broader hybrid activities. The selec­tive measures taken to date – and their resulting inadequacy – provide Russia with both operational freedom and strategic ini­tiative. This allows Moscow to continue its extensive oil exports while simultaneously sustaining hybrid activities through both military and non-military means below the threshold of armed conflict.

Because countermeasures have so far targeted individual vessels and therefore produced only limited systemic impact, future measures must be designed as a co­ordinated system. If Europeans aim to act more effectively against Russian sanctions evasion and war financing, measures tar­geting the shadow fleet need to be imple­mented across multiple levels and in a significantly more coordinated manner. Only then can they achieve a lasting effect in containing the shadow fleet and reduc­ing Russian revenue flows.

However, it is essential not to succumb to the illusion that this would make it pos­sible to stop all shadow fleet vessels immedi­ately. This is neither legally nor practically feasible. The following four measures to­gether form an overarching approach aimed at making full use of the existing legal frame­work on the basis of international law. At the same time, concrete and sustainably deterrent methods can be applied.

Sanctions regime

First, the phenomenon of the Russian shad­ow fleet – and thus the sanctions regime – must be taken to its logical conclusion. On the one hand, sanctions lists maintained by the EU, the United Kingdom, the United States, and Canada must be continuously synchronised in order to achieve broad effectiveness. On the other hand, the mere sanctioning of vessels must be followed by further action. By now, almost every second tanker used for Russian oil exports has been sanctioned, yet this has had little impact on sales. Sanctions mechanisms therefore urgently need to be extended to include intermediary ports of call, refineries, and companies in third countries that facilitate transactions and trade flows. This would also imply that EU states cease importing oil indirectly via intermediaries such as Turkey and India. In this respect, national-level measures in particular are required.

The restrictions on maritime traffic in the Strait of Hormuz highlight this need for coordination. Rising oil prices, combined with a partial easing of US sanctions – such as exemptions for India – is generating substantial additional revenues for Rus­sia as an exporting state. At the same time, the US rationale is based on the assumption that short-term sanctions relief will help sta­bilise global oil prices and thereby reduce Russian export revenues. While emergency measures for global market and oil price stabilisation can be justified, they should be realigned as soon as possible with the strategic objective of containing the shadow fleet, if the goal is to limit Russian revenues and war financing.

Flag states and ownership structures

Second, insufficient flag registration of shadow fleet vessels continues to offer room for manoeuvre that is not being fully utilised. Diplomatic and economic pressure on states offering “flags of convenience” must also be significantly increased. A suit­able starting point is the open letter from the North and Baltic Sea littoral states, in­cluding Iceland, to the international com­munity. It calls for compliance with the enforcement of general shipping standards and maritime safety within an international framework. As a result of growing pressure on the shadow fleet, some states have stopped making their flags available for such vessels. In this way, available options for operators of these ships are gradually being reduced.

In parallel, ownership structures and ves­sel sales should be scrutinised more closely. The actors involved should also face eco­nomic consequences at the EU level or at the level of individual nation states, as Euro­pean and also German shipping com­panies continue to sell vessels that are sub­sequently used for the shadow fleet, there­by facilitating sanctions evasion. Restricting these onward sales represents another means of reducing the physical basis for exports and sanctions circumvention.

Environmental protection as an option for action

Third, environmental protection must also be used as a basis for action. In the North and Baltic Seas, the additional protection requirements of these sea areas – classified by the International Maritime Organization (IMO) as “Particularly Sensitive Sea Areas” (PSSA) – offer untapped scope for action. Under this classification, the North and Baltic Seas are considered especially vulner­able and, in this respect, are placed on the same level as well-known marine regions such as the Galápagos Islands and the Great Barrier Reef.

The numerous documented cases of un­seaworthy tankers, as well as accidents and groundings, suggest that the deliberate use of vessels with minimal or no seaworthiness effectively amounts to an acceptance of environmental harm. Germany and its partner coastal states in the North and Bal­tic Seas should take this as grounds for meeting their responsibility towards these maritime regions and should more fre­quently stop, inspect, and, where necessary, deny passage to ageing tankers on account of their poor condition. This would protect sea areas from accident-related and envi­ronmental risks, while also further slowing and reducing shadow fleet operations.

For these two reasons, such measures should not be limited to the Russian shad­ow fleet but extended to all ageing vessels that may pose environmental risks. In its response to a minor interpellation in the Bundestag, the Federal Government has already stated its view that such measures can help curb the transit of the shadow fleet while also preventing accidents and environmental damage. It is therefore now crucial to put these findings into practice.

Defence dimension

Fourth, Russia’s further development of the shadow fleet from a predominantly eco­nomically motivated instrument into a tool of hybrid warfare must be recognised as a national security threat and, in certain con­stellations, as a militarily relevant challenge. If this is accepted, it opens up addi­tional options for action vis-à-vis shadow fleet vessels. Spying, sabotage, the use of drones, and the presence of (para)military personnel on board appear to be increasing. This suggests that the shadow fleet no longer serves exclusively commercial pur­poses. There is considerable evidence that its activities are deliberately employed in the grey zone below the threshold of armed conflict. This is consistent with Kremlin rhetoric, which already frames relations with NATO as a structural conflict.

This development implies that such vessels are no longer to be classified solely within the domain of maritime safety and security, but must additionally be situated within the framework of national security and defence. This broadens the scope for action: The non-peaceful use of vessels pro­vides stronger grounds for legitimate meas­ures such as stopping, inspecting, detaining, or ordering them to leave, since the right of innocent passage applies only to ships that do not pose a threat.

Managing threats and risks

Activities aimed at containing the shadow fleet must also be considered in the context of potential escalation dynamics and rules of engagement, that is, beyond the purely operational level. It is not sufficient for procedures to be rehearsed within police, military, and NATO frameworks. Decision-makers must also be familiarised with the escalatory risks of possible measures against vessels associated with the Russian shadow fleet and be prepared to address them. This requires, first, that states do not allow them­selves to be intimidated by Russian accusations, threats, or military power projection. Instead, it is essential for states to stand together, and within an international framework, behind measures such as vessel inspections or denial of entry into certain maritime zones, and to implement them consistently and without hesitation. A coherent and resolute approach would render Russian threats ineffective.

In addition to the four measures, prudent and strategically oriented security policy preparation is therefore required. This involves anticipating in advance the possible actions of actors who may deliber­ately employ the risk of military or even nuclear escalation as a strategic tool. What if crews of shadow fleet tankers refuse to cooperate with German or Western author­ities, or are prevented from doing so by (para)military personnel on board? Russia is exploiting its position and capabilities to keep such options available. Both vertical and horizontal escalation scenarios are con­ceivable. Vertical escalation refers to the use of military force, supported by threats and coercive rhetoric, whereby Russia does not exclude the nuclear dimension. Hori­zontal escalation refers to the possibility of multiple, simultaneously induced incidents of damage, such as the destruction of criti­cal infrastructure, port blockades, or delib­erately triggered environmental disasters. To prevent a recurrence of cases such as the Jaguar, such scenarios must be addressed not only at the operational and military levels, but also politically and legally among the federal and state authorities, ministries, and partner states, and as early as possible, rather than in the midst of an already esca­lating crisis.

It is necessary to analyse potential Russian options for escalation and coercion, to work through possible consequences, and to prepare concretely for such crises. In this way, courses of action for possible conflicts and prospective escalation dynamics can be developed. This helps to raise awareness of the underlying problem among decision-makers, to minimise friction between the relevant authorities in the event of a con­frontation, and to assess and optimise one’s own response capabilities.

It should be noted that it is not necessarily the individual damaging incident that con­stitutes the serious problem. Rather, it is the cumulative generation of such events that can ultimately become part of an esca­lating dynamic and, when accompanied by (nuclear) signalling and threats, test the resolve of decision-makers. In this way, Russia repeatedly seeks to deter measures against its shadow fleet, given its depend­ence on maritime routes via the Baltic and North Seas.

The Federal Republic of Germany and its European partners must be prepared for provocations and attempts at coercion if they follow these recommendations and imple­ment the four proposed measures. What matters is that they remain undeterred and implement this catalogue of measures in a determined, systematic, and sustained manner. If they do so, the prospects of con­taining shadow fleet shipping on a lasting basis are favourable.