In the western Baltic, a coast guard officer radios in on a nearby sanctioned oil tanker.
“The Swedish Coast Guard is calling… Are you willing to answer a few questions for us? It's over.”
Through the heavy static, the crew member's responses crackle barely audibly as he gradually lists the ship's insurance details, flag state and final port of call – Suez, Egypt.
“I think this ship will go to Russia and deliver oil,” says Swedish investigator Jonathan Tolin.
This is the front line of Europe’s difficult confrontation with Russia’s so-called “shadow fleet”; a term that usually refers to the hundreds of tankers used to circumvent price restrictions on Russian oil exports.
After the Kremlin launched a full-scale invasion of Ukraine, many Western countries imposed sanctions on Russian energy, which Moscow is accused of evading by transporting oil on outdated tankers, often with unclear ownership or insurance.
European coast guards and navies regularly come into contact with vessels from Russia's shadow fleet that they suspect are carrying oil. [BBC]
Some “shadow” ships are even suspected of underwater sabotage, illegally launching drones, or “faking” data about their location.
In waves where freedom of navigation is the golden rule, the ability and willingness of coastal countries to intervene is limited, although the risk they face increases.
A growing network of “shadow” vessels are sailing without a valid national flag, which could leave the vessels stateless or without proper insurance, the BBC has learned.
It's a worrying trend, given that many of them are practically “floating rust buckets,” says Windward AI senior naval intelligence analyst Michele Wiese Bockmann. If an accident occurs, such as a billion-dollar oil spill, “good luck finding someone responsible who will bear any costs.”
Thanks to record sanctions and tougher enforcement, the number of false flag vessels worldwide has more than doubled this year to more than 450, most of them tankers, according to an International Maritime Organization (IMO) database.
The BBC tracked one ship that appeared to be sailing without a valid flag.
The head of the Estonian Navy, Commodore Ivo Värk, says ships sail back and forth past Estonia to major Russian oil terminals. [BBC]
The head of the Estonian Navy, Commodore Ivo Värk, says they have seen dozens of such vessels passing this year, whereas previously they only saw one or two.
The growth is alarming, he tells me as we chat in his office overlooking the Gulf of Finland, the narrow gateway to the major Russian oil terminals of Ust-Luga and Primorsk.
Moreover, he believes, it is brazen: “It’s not a secret.”
We spot the tanker Unity in the MarineTraffic app the day we board the Estonian (UK-built) Minhunter, which is also used on NATO Baltic Sentry patrols to protect critical infrastructure.
Heading east, Unity is over 100 miles away, but sailing in our direction.
The BBC has looked into its history and offers insight into the shadow ship's mysterious life.
Tracking data shows Unity has crossed the English Channel four times in the past twelve months, including voyages between Russian ports and India; a key oil buyer who did not agree to a price cap.
The tanker, originally known as Ocean Explorer, was built in 2009 and sailed under the Singapore flag for more than a decade.
Back in 2019, it was mentioned in a UN report for its alleged involvement in ship-to-ship transfers that were sanctioned for their role in transporting fuel to North Korea. which, among other countries, is also accused of using elusive shadow ships.
By the end of 2021, the vessel, which was operating as Ocean Vela that year, had adopted a Marshall Islands flag, but was delisted in 2024, a registry spokesman told us, because the vessel's then operator and beneficial owner company were subject to UK sanctions.
The tanker appears to have had three more names since 2021 (Beks Swan, March and Unity) and three more flags (Panama, Russia and Gambia), but always retains a unique IMO number.
In August, ship broadcast data shows Unity claiming ownership of the Lesotho flag, which was labeled as “false”. Lesotho is a small landlocked African enclave kingdom that, according to the IMO, has no official registry.
The BBC attempted to contact the registered owner of Unity, a Dubai-registered company called FMTS Ship Charter LLCbut our emails and calls went unanswered.
According to maritime intelligence company Windward AI, the beneficial owners of 60% of the vessels in the shadow fleet remain virtually unknown.
Opaque ownership structures, as well as frequent changes of names or flags, have become a hallmark of the shadow fleet as a means of avoiding detection.
Scratched from reputable registries and passed over by inferior alternatives, some ships are now at a stage “where they're not even bothered at all,” says Michel Wiese Bockmann.
Unity's latest voyage saw it sail through the North Sea at the end of October before entering the Baltic Sea and passing through countries such as Sweden and Estonia – which is where we spotted it.
By November 6, it was anchored near the Russian port of Ust-Luga, where it remains at the time of publication.
The tanker was added to the growing list of UK and EU vessels under sanctions earlier this year but, like many others, continues to do business despite other difficulties.
Back in January, he reportedly took refuge in the English Channel after suffering mechanical failure during a storm. It is reported that next August detained in a Russian port due to technical problems and non-payment of wages.
Unity is just one of hundreds of ships subject to UK and EU service and port bans as both London and Brussels are trying to increase pressure on the Kremlin.
However, according to the Paris-based International Energy Agency (IEA), Russia's revenues from oil and petroleum products totaled $13.1bn (£9.95bn) in October alone, although that figure was down $2.3bn on the same month last year.
Analysis by the Center for Energy and Clean Air Research finds that sanctioned or suspect “shadow” tankers account for 62% of shipped Russian crude oil exports, while China and India are the largest oil buyers, followed by Turkey and the European Union itself.
While politicians talk of tightening measuresNavy and Coast Guard officers say the nation's ability to operate weakens as it goes to sea.
The right of innocent passage remains a cornerstone of the law of the sea, but stateless ships are technically not entitled to it.
Countries such as France, Finland and Estonia detain ships and can do so if a crime is suspected, but such tight controls remain relatively rare.
“There is a difficulty with this,” says Commodore Ivo Värk. “Given the Russian presence close to our borders, the risk of escalation is too high to do this on a regular basis.”
Estonians speak from experience.
When they tried to intercept an unflagged tanker in May, Russia briefly deployed the fighter jet and has had about two warships in the Gulf of Finland “at all times” since then, says Commodore Värk.
The fear of escalation sits alongside broader fears of commercial retaliation if a more aggressive approach is adopted.
“Every day there is suspicious activity in the Baltics,” a NATO spokesman told the BBC on condition of anonymity. Still, the official added, “We don’t want to be cowboys and jump on ships. “Surveillance of ships is a deterrent in itself.”
“Freedom of navigation is the lifeblood of all our economies.”
On the bridge of the Swedish coast guard ship, radio contact with the sanctioned tanker ended.
“Thank you for your cooperation,” the officer says as the ship moves toward Russia.
The conversation lasted a little over five minutes.
“We need to look at this from a broader perspective,” says investigator Jonathan Tolin, when I suggest that these measures seem less than stringent: “This information can be used in our maritime surveillance.”
But as Europe ramps up checks and watches the ripples, Windward's Michele Wiese Bockmann notices something else: “You can literally see the rules-based international order crumbling because of the sanctions-busting tactics of these courts.”
There's a lot at stake for the environment and safety, she said, and meanwhile “the dark fleet is getting darker.”
The BBC has contacted the Russian Embassy in London for comment. In response, the representative said that the West's “anti-Russian sanctions” are “illegitimate” and “undermine the established principles of global trade.”
“Labeling vessels used to export Russian oil as ‘shadow fleet’ is discriminatory and misleading,” the embassy said, and cases of invalid flags were usually down to “easily solvable” problems such as administrative delays.
It is the sanctioned countries that have “increased” the risks, “forcing shipowners and operators to navigate an increasingly fragmented and restrictive regulatory environment,” the spokesperson said.
Additional reporting by Adrienne Murray, Michael Steininger and Ali Zaidi.
