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.
That is a troubling trend, given many are practically floating rust buckets, says senior maritime intelligence analyst at Windward AI, Michelle Wiese Bockmann. If there is an accident, like a billion-dollar oil spill, good luck with trying to find somebody responsible to pick up any cost.
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 BBC has been tracking one ship that appears to have sailed without a valid flag.
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.
The rise is alarming, he tells me, as we talk in his office overlooking the Gulf of Finland, a narrow gateway to the major Russian oil terminals of Ust-Luga and Primorsk.
What's more, he suggests, it's brazen: There's no secret made about it.
We spot the tanker Unity on the MarineTraffic app, the day we board an Estonian (British-built) Minehunter that is also used in Nato's Baltic Sentry patrols to protect critical infrastructure.
Journeying east, Unity is over 100 miles away but sailing in our direction.
The BBC has investigated its history - it offers an illuminating insight into the enigmatic life of a shadow ship that has passed through the English Channel four times in the last twelve months.
The Estonians speak from experience.
When they attempted to intercept a flagless tanker in May, Russia briefly deployed a fighter jet and has constantly had about two naval vessels in the Gulf of Finland since, says Commodore Värk.
The fear of escalation sits alongside concerns of commercial retaliation if a more aggressive approach were to be taken.
As Europe steps up checks and watches the waves, Windward's Michelle Wiese Bockmann spies something else: You can literally see the international rules-based order crumbling through the sanctions-circumventing tactics of these vessels.
Back on the bridge of the Swedish coastguard ship, the radio call with the sanctioned tanker has wrapped up. Thank you for your co-operation, says the officer as the vessel carries on towards Russia.
