Under steel grey skies, the Dutch minehunting vessel Schiedam cuts through the waters dividing Denmark and Sweden, part of NATO's Baltic Sentry mission to protect underwater infrastructure in the Baltic Sea.

At a time when the eight NATO nations bordering the Baltic Sea are on high alert after a string of undersea power and internet cables were suspiciously severed, Russia's shadow fleet is getting extra attention.

A Bulgarian ship has been released after Swedish authorities cleared it of deliberately sabotaging an underwater cable in the Baltic Sea. NATO has moved to protect Baltic Sea cables amid concerns of Russian tampering.