Rising tensions with Russia have NATO militaries worried about the revival of a Cold War-era submarine threat

• NATO militaries are wary of the expanding capability and activity of Russia's submarine fleet.
• A top concern is that those subs could be used to attack or interfere with undersea cables and pipelines.
• For NATO navies, finding and tracking those subs in the open ocean is a challenging task.

NATO militaries have grown increasingly concerned about Russia's underwater capabilities, worrying that Moscow's attack and ballistic-missile submarines and special-purpose submersibles could be used to menace or attack their economic and military infrastructure.

French President Emmanuel Macron is the latest leader to warn about the threat, stating the importance of underwater security in a speech to the French military on January 20.