By bizn_fun 
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 broader concerns of commercial retaliation if a more aggressive approach were to be taken.
“Every day in the Baltic, there’s suspicious activity,” a Nato official told the BBC, speaking on the condition of anonymity. Nevertheless, the official added, “we don’t want to be cowboys and jumping on ships. The act of monitoring ships is a deterrent in itself”.
“Freedom of navigation is the lifeblood of all of our economies.”
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.
The exchange lasted just over five minutes.
“You need to see it in a larger perspective,” says investigator Jonatan Tholin when I suggest these measures appear less than muscular: “This information can be used in our maritime surveillance.”
But 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.”
There is a lot at stake for the environment and on security, she says, and meanwhile “the dark fleet is getting darker”.
The BBC approached Russia’s embassy in London for comment. In response, a spokesman said that the West’s “anti-Russian sanctions” were “illegitimate” and “undermine established principles of global commerce”.
“Labelling ships used to export Russian oil as ‘shadow fleet’ is discriminatory and misleading,” the embassy said, and instances of invalid flags were typically down to “easily resolved” issues such as administrative delays.
It was sanctioning countries, the spokesperson said, that had “heightened” the risks by “forcing shipowners and operators to navigate an increasingly fragmented and restrictive regulatory landscape”.
Additional reporting by Adrienne Murray, Michael Steininger and Ali Zaidi