Russian “shadow fleet” tanker without valid registration slips through Estonian waters at night to avoid seizure

The oil tanker Marathon, part of Russia’s so-called “shadow fleet,” attempted to pass unnoticed through Estonia’s Exclusive Economic Zone (EEZ) during nighttime hours in order to avoid possible interception and inspection. According to data analyzed by The Insider in collaboration with Starboard Maritime Intelligence, the vessel had no valid registration at the time — a fact that would have given Estonian authorities the legal grounds to board and detain the ship.

Estonia had previously detained the tanker Kiwala and attempted to stop the Jaguar — both of which are part of Russia’s “shadow fleet,” a collection of aging, poorly insured vessels that transport oil in circumvention of the $60-per-barrel price cap introduced by the G7, the EU, and Australia in 2022. The fleet has allowed the Kremlin to continue to line its coffers and finance the ongoing full-scale invasion of Ukraine, which entered its fourth year in February 2025.

The Marathon crossed the Baltic Sea between June 11 and 13. Before entering Estonian waters, the vessel slowed down significantly and remained nearly stationary for approximately 28 hours. It then sped through Estonia’s EEZ shortly before sunrise — at around 4:00 a.m. UTC on June 13.

During the crossing, Marathon did not anchor or stop and proceeded directly toward Russia. No boarding or escort by Estonian authorities was observed.

Mark Douglas, a maritime domain analyst at Starboard Maritime Intelligence, told The Insider that the ship’s extended delay and choice to transit before daylight strongly suggest the crew aimed to minimize their time in Estonian waters — particularly during daylight hours, when the risk of aerial surveillance or boarding by authorities is higher. Boarding operations at night are generally avoided due to poor visibility and safety risks, as well as the potential diplomatic fallout from any missteps.

Interestingly, the Marathon did not speed up in areas where other vessels had previously been intercepted — such as near the capital, Tallinn — indicating the crew likely timed their passage carefully rather than simply trying to rush through Estonian waters.

Legally, as Douglas pointed out, Estonian authorities had the right to stop the tanker. Though the ship broadcasted an AIS signal indicating it was flying the flag of Cameroon, it had in fact lost its registration with Djibouti after being sanctioned by the EU — leaving it effectively flagless. According to international law, the absence of a valid flag can justify boarding and inspection by coastal states.

“Marathon’s timing strongly suggests it sought to avoid even the possibility of a compliant boarding by transiting at night and not anchoring, effectively removing the window for legal engagement,” Douglas noted.

On June 15, the Marathon entered the port of Primorsk in Russia’s Leningrad Region. Satellite data from Starboard indicates its draft increased there — meaning it got “heavier,” presumably due to cargo being loaded. The vessel departed the next day, with its current listed destination as Port Said, Egypt. The Marathon is under sanctions from the UK, EU, and Canada.

This incident marks the fourth time in just two months that an unregistered tanker has entered the Baltic Sea. Unsurprisingly, the other three instances also involved ships suspected of activities connected to Russia’s “shadow fleet.”

• On April 11, Estonia detained the Kiwala, a “shadow fleet” tanker flying the Djibouti flag. It was found to be missing from all ship registries and released on April 26 after 40 safety violations were corrected.
• On May 14, Estonian authorities attempted to detain the Jaguar, a so-called “civilian vessel” that, according to The Insider, also belongs to Russia’s “shadow fleet.” On May 13, a Russian Su-35 aircraft violated Estonian airspace in the area of the tanker. Like the Kiwala, the Jaguar was sailing without a flag.
• On May 24, another unregistered tanker — the Falcon — appeared in the Baltic Sea. Its behavior also suggested links to Russia’s “shadow fleet.”

Four days after the Jaguar incident, Russia retaliated by detaining a tanker that had departed from the Estonian port of Sillamäe.