Out on the western Baltic, a coastguard officer radios a nearby, sanctioned oil tanker.
Swedish Coastguard calling… Do you consent to answer a few questions for us? Over.
Through heavy static, barely audible answers crackle over from a crew member, who gradually lists the ship's insurance details, flag state and last port of call – Suez, Egypt.
I think this ship will go up to Russia and get oil, says Swedish investigator, Jonatan Tholin.
This is the front line of Europe's uneasy standoff with Russia's so-called shadow fleet; a term that commonly refers to hundreds of tankers used to bypass a price cap on Russian oil exports.
After the Kremlin launched its full-scale invasion of Ukraine, many Western countries imposed sanctions on Russian energy, which Moscow is accused of dodging by shipping oil on aged tankers often with obscure ownership or insurance.
Some shadow ships are even suspected of undersea sabotage, illicit drone launches or spoofing their location data.
Out on the waves, where freedom of navigation is a golden rule, the ability and appetite of coastal countries to intervene is limited, even though the risk they face is escalating.
As the BBC has learned, a growing network of shadow ships are sailing without a valid national flag, which can render vessels stateless and without proper insurance.
Driven by record sanctions and tighter enforcement, the number of falsely flagged ships globally has more than doubled this year to over 450, most of them tankers, according to the International Maritime Organization (IMO) database.
The head of Estonia's navy, Commodore Ivo Värk, says they have seen dozens of such passing vessels this year whereas they used to see just one or two.
Tracking data shows that Unity has passed through the English Channel four times in the last twelve months, including journeys between Russian ports and India; a key oil customer that has not signed up to the price cap.
The tanker appears to have had three further names since 2021 (Beks Swan, March and Unity) and three further flags (Panama, Russia and Gambia) but always retains a unique IMO number.
This system of opaque ownership structures, along with frequent name and flag changes, has become a signature trait of the shadow fleet, allowing them to avoid detection.
The BBC has tried to contact Unity's listed owner, a Dubai-registered company, but our emails and calls went unanswered.
The beneficial owners of 60% of shadow fleet vessels remain essentially unknown, reflecting the challenges authorities face.
Despite Western sanctions and pressures, Russian revenues from crude oil sales, particularly to countries like China and India, continue to pose significant geopolitical challenges as Europe wages its battle against this shadow fleet.
The article highlights the complexities faced by coastguards tasked with navigating these choppy waters amidst rising tensions and escalating risks.
