The majority of critical undersea infrastructure is located in international waters, which means would-be saboteurs can take advantage of oversight gaps.

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.

Northern Europe’s Baltic Sea is bordered by nations including Germany, Russia and Latvia. Many critical cables and pipelines cross the seafloor. But with tensions rising in the region, NATO is looking for ways to ensure all that infrastructure stays safe.

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.