Russian Warships Guard Shadow Tankers

A Russian destroyer has been sitting off Fehmarn, the German island in the Baltic. In the Gulf of Finland, corvettes armed with cruise missiles have escorted sanctioned oil tankers through waters now bordered almost entirely by NATO states. Estonia's navy commander says boarding them has become too dangerous. The result is a hard lesson in deterrence: EU sanctions may list the tankers, but Russian warships are making European navies think twice before enforcing them at sea.

What Triggered the Escorts

The ships at the centre of this are Russia's "shadow fleet": ageing tankers, often using flags of convenience, moving Russian oil around Western price caps. The EU has sanctioned hundreds of them across successive packages (Ashurst). Putting a vessel on a sanctions list is the easy part. Stopping it on the water is where law, politics and force collide.

The shift came in December 2024, when Finnish authorities seized the tanker Eagle S in the Gulf of Finland on suspicion of damaging undersea cables (ACLED). A Nordic state had used physical authority against a shadow vessel. Moscow answered by putting naval steel around the trade. By June 2025, the corvette Boiky was escorting sanctioned tankers through the English Channel (Naval News). By spring 2026, two to three Russian warships were on standing patrol in the Gulf of Finland. Estonia's Navy Commander Ivo Vark said the risk of detaining shadow fleet vessels is now "too high" (Kyiv Independent).

Off Germany, the destroyer Severomorsk took position near Fehmarn in early May. Berlin sent the reconnaissance ship Oste in response, with its transponder switched off. Germany's defence ministry described Moscow's purpose plainly: to "monitor and secure its own shadow fleet" (NDR, Der Spiegel).

Sweden has taken a different route. Since March, its coast guard has boarded suspected shadow fleet vessels near Trelleborg, using maritime safety law rather than sanctions as the legal hook (SVT). But Sweden is doing this well away from Russian naval patrols. The map matters as much as the law.

The Gap Between List and Law

The shadow fleet has exposed a weakness in Europe's security machinery. EU sanctions can name vessels and ban them from ports. NATO's Baltic Sentry operation can monitor undersea infrastructure. EMSA, the EU's maritime safety agency, can provide satellite surveillance. None of that gives anyone the power to board a ship.

That power sits with national coast guards under UNCLOS, the UN Convention on the Law of the Sea. UNCLOS does not treat "sanctioned vessel" as a legal basis for stopping a ship. European states have worked around this by using false-flag registration or safety violations as triggers. Russia is already trying to close that opening by reflagging shadow fleet tankers under the Russian flag, removing the "stateless vessel" argument on which some boarding operations depend (ACLED).

Three Countries Hold the Veto

Baltic and Nordic foreign ministers signed the Sopot Declaration in late May, calling for "decisive steps", including a full ban on maritime services for Russian energy exports (Polish MFA). The measure that would hurt most, a total EU ban on insurance, transport and maintenance for ships carrying Russian oil, has been blocked by Greece, Cyprus, and Malta, whose shipping industries have a direct financial stake (Greek Reporter).

This is where the familiar EU mechanism bites. Foreign policy decisions under CFSP, the bloc's foreign-policy framework, require unanimity. Any member state can veto. The latest sanctions package created the legal framework for the ban, but made activation conditional on "unanimous agreement". In practice, that means postponement with no fixed end. The Commission plans to bring it back in the next package, expected in late June. There is no verified evidence that the blocking coalition has moved.

A Lake With a Hole in It

EU sanctions were designed to change commercial incentives: remove insurance, close ports, make evasion uneconomic. They were not built for a situation in which Russian warships escort sanctioned tankers through allied waters. NATO can monitor, but it cannot enforce sanctions law. The EU can designate vessels, but it cannot board them. Coast guards can board, but may then face armed confrontation. The Atlantic Council found that, even after Finland and Sweden joined NATO and shifted the conventional balance in the Baltic, the alliance still struggles to deter threats kept just below the threshold of open war (Atlantic Council).

The Baltic was meant to become a NATO lake. Russia has found the hole in it. Whether Europe's sanctions regime remains a legal framework on paper, or becomes enforceable at the waterline, now depends on whether the next package can break the Mediterranean veto before Moscow's escort doctrine settles into routine.