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.

Macron wished for his country to "acquire a capacity to control the seabed" to depths of 19,600 feet, citing "military reasons" and the protection of "critical underwater infrastructure" as the imperatives behind his call, without explicitly mentioning Russia.

France's has numerous overseas territories that give Paris the world's second largest exclusive economic zone, which refers to an area extending 200 nautical miles from coastline where countries have exclusive rights.

This creates an "immense benefit" but also an "immense responsibility" to protect infrastructure and territory, Macron said.

The sabotage of the Nord Stream gas pipelines in the Baltic Sea in late September highlighted longstanding concerns about the "vulnerability" of underwater infrastructure, the chief of the British naval staff said after the pipelines were damaged.

Officials have not been able to prove that Russia was behind the Nord Stream attacks, but the incidents have only added to NATO's concerns about Russia's underwater capabilities. This week, NATO announced that it would set up a "coordination cell" to help militaries and industry work together "and boost the security of Allied undersea infrastructure."

Allied concern

Concern about Russia's expanding underwater capabilities and the danger they pose to critical underwater infrastructure has risen since Russia seized Crimea in 2014.

Since then, Russian submarines have deployed more often and for longer and their activity close to critical undersea infrastructure has increased. "We are now seeing Russian underwater activity in the vicinity of undersea cables that I don't believe we have ever seen," the US Navy admiral in charge of NATO's submarine forces said in 2017.

Protecting that infrastructure is feasible in relatively shallow waters and close to naval bases, conditions that exist in the Baltic and Nordic seas, if sufficient submarine-detecting sensors are placed in the right areas, said Tuomas Pöyry, vice president of Image Soft, a Finnish company that develops underwater surveillance systems.

However, the North Atlantic, through which many such cables pass, "is such a deep and wide area" that even if cables were protected with sensors and an approaching threat were detected, "by the time the defending force would go to the site, the cables and pipes would have already been destroyed and the offending sub would be long gone," Pöyry, who is also a captain in the Finnish military reserve, told Insider.

Russia has invested heavily in modernizing its submarine fleet, which has grown to 58 vessels, although 10 of them are more than 35 years old. The most worrying component of that expansion are the Yasen-class submarines. Two have entered service since 2014 and a third is undergoing sea trials.

Yasens are considered especially quiet and carry land-attack cruise missiles that NATO commanders worry could be used to attack vital infrastructure in Europe or the US if those subs are able to slip into the Atlantic during a war.

Recent Russian submarine activity does suggest an increasing focus on being able to get into the Atlantic and closer to the US East Coast.

In 2019, 10 Russian submarines, eight of them nuclear-powered, conducted a surge deployment from Arctic bases into the North Atlantic with the apparent aim of sailing as far as possible without being detected by NATO.

Vice Adm. Daniel Dwyer, commander of the US Navy's Virginia-based 2nd Fleet — which was reactivated in 2018 in response to growing naval threats — said in 2022 that the Atlantic "no longer provided that geography" that enabled the defense of the mainland US "that we've enjoyed for so many decades."

Russia also continues building quiet diesel-electric Kilo II-class subs specialized for reconnaissance and anti-submarine warfare and has built at least two large nuclear-powered subs that Western experts believe are designed to launch smaller submersibles that could tap or attack undersea cables or pipelines.

Nuclear-powered subs have several advantages over conventionally powered subs: They are generally larger and can carry more weapons and can sail faster and over longer distances.

Nuclear-powered submarines with reactors designed to minimize the noise they make are "the most difficult" to detect, Pöyry told Insider.

"If a modern nuclear submarine dives and settles on the seabed to hide and wait, it is almost impossible to detect except if you happen to actively pinging it just on the right spot with an active sonar," Pöyry said.

But a submarine that moves will make noise, "and even silent nuclear submarines can be heard in right conditions tens of kilometers away," Pöyry said.

Underwater sleuthing

Attacking enemy warships, especially aircraft carriers, and enemy infrastructure, like ports, was a primary mission for Soviet attack and cruise-missile submarines during the Cold War, and keeping tabs on those subs was a major concern for NATO militaries.

Early in the Cold War, the US developed the Sound Surveillance System, or SOSUS, a classified network of sonars meant to detect and identify Soviet submarines in the strategically located Greenland-Iceland-UK gap in the North Atlantic.

Information about SOSUS was eventually leaked to the Soviets, reducing its effectiveness, but the US ran the network until the end of the Cold War. The US also obtained intelligence on Soviet subs through covert operations, including the recovery of part of a sunken K-129 ballistic-missile sub in 1974 and the tapping Soviet naval communications.

While the Russian navy fell into disrepair after the Cold War, NATO's focus on finding and tracking Russian subs has intensified in recent years as Moscow has strengthened its undersea fleet and shown the ability to strike target deep inland with new cruise missiles.

Experts have said new technologies will make detecting enemy subs more complex than ever in the years ahead. NATO militaries are guarded when describing their own capabilities to find those subs, but officials have acknowledged that they can't see everything they want to see.

At a Senate hearing in February 2020, the head of US European Command was asked if US forces have "sufficient visibility" on Russian submarines in the Atlantic. "We do but not for 100% of the time," he replied.

Constantine Atlamazoglou works on transatlantic and European security. He holds a master's degree in security studies and European affairs from the Fletcher School of Law and Diplomacy. You can contact him on LinkedIn.