NATO navies are ramping up its defence in the Baltic and North Seas as Russia’s so-called “shadow fleet” of deceptive vessels grows rapidly, raising fears of espionage and sabotage against critical infrastructure.

The number of shadow ships—tankers and cargo vessels that conceal their identity or switch flags—has soared from around 200 in 2022 to about 1,000 today, according to maritime intelligence firms. Originally used to smuggle sanctioned oil, many are now suspected of cutting undersea cables, spying with drones, and intimidating NATO allies.

Estonia, on the front line of the threat, tracks dozens of shadow vessels daily in the Gulf of Finland but says it has little power to stop them.

“There’s not much we can do,” admitted Commodore Ivo Värk, the Estonian navy chief, after Russia scrambled fighter jets to shield one tanker from detention.

The “grey-zone” tactics recall practices pioneered by North Korea and later Iran and Venezuela—such as going dark, ship-to-ship transfers, and fake flag registries. But Russia’s scale is unprecedented - nearly one-fifth of the world’s tanker fleet is now classified as shadow tonnage.

Western prosecutors struggle to prove sabotage cases, as ships often use shell companies and fictitious registries. Some even fly flags of non-existent states according to experts.

In response, NATO has launched Baltic Sentry, a mission to protect undersea cables and pipelines. Estonia has also authorised its navy to attack civilian vessels if they damage its infrastructure.

Analysts say shadow fleets will persist beyond the Ukraine war, having exposed gaps in global maritime governance.

“This is a giant floating platform for criminals and hostile regimes,” said Richard Meade of Lloyd’s List.

“The genie isn’t going back into the bottle.”

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