'ABOARD THE HNLMS LUYMES—Belgian Navy Commander Erik Kockx was patrolling the Baltic Sea recently when he got word that a ship on NATO’s watchlist was acting in a suspicious manner. After leaving a Russian port, it had slowed down while passing near a pipeline on the sea bottom. The Luymes sailed toward the tanker to investigate...

When Kockx’s ship recently approached the suspect tanker, which was part of Russia’s “shadow fleet” of illicit fuel transporters, it regained speed and sailed on.

“It’s quite difficult to prove that our presence helps. It’s hard to say that if we hadn’t been there, something would have occurred,” said Kockx as cargo ships floated by in the distance. But just as drivers become more attentive when they see a police car, “we’ve seen behavior get better,” he said of seamanship. “Ships know they’re being watched.”'