With its powerful camera, the French Navy surveillance plane scouring the Baltic Sea zoomed in on a cargo ship plowing the waters below—closer, closer, and closer still until the camera operator could make out details on the vessel’s front deck and smoke pouring from its chimney.

The long-range Atlantique 2 aircraft on a new mission for NATO then shifted its high-tech gaze onto another target, and another after that until, after more than five hours on patrol, the plane’s array of sensors had scoped out the bulk of the Baltic—from Germany in the west to Estonia in the northeast, bordering Russia.

The flight’s mere presence in the skies above the strategic sea last week, combined with military ships patrolling on the waters, also sent an unmistakable message: The NATO alliance is ratcheting up its guard against suspected attempts to sabotage underwater energy and data cables and pipelines that crisscross the Baltic, prompted by a growing catalogue of incidents that have damaged them.

“We will do everything in our power to make sure that we fight back, that we are able to see what is happening and then take the next steps to make sure that it doesn’t happen again. And our adversaries should know this,” NATO Secretary-General Mark Rutte said this month in announcing a new alliance mission, dubbed “Baltic Sentry,” to protect the underwater infrastructure vital to the economic well-being of Baltic-region nations.

Power and communications cables and gas pipelines stitch together the nine countries with shores on the Baltic, a relatively shallow and nearly........

© Fast Company