NAPLES, Italy — Russian attack submarines, the most in two decades, are prowling the coastlines of Scandinavia and Scotland, the Mediterranean Sea and the North Atlantic in what Western military officials say is a significantly increased presence aimed at contesting U.S. and NATO undersea dominance.
Adm. Mark Ferguson, the U.S. Navy's top commander in Europe, said last fall that the intensity of Russian submarine patrols had risen by almost 50 percent over the past year, citing public remarks by the Russian navy chief, Adm. Victor Chirkov. Analysts say that tempo has not changed since then.
The patrols are the most visible sign of a renewed interest in submarine warfare by President Vladimir V. Putin, whose government has spent billions of dollars for new classes of diesel and nuclear-powered attack submarines that are quieter, better armed and operated by more proficient crews than in the past.
The tensions are part of an expanding rivalry and military buildup, with echoes of the Cold War, between the United States and Russia. Moscow is projecting force not only in the North Atlantic but in Syria and Ukraine and building up its nuclear arsenal and cyberwarfare capabilities in what U.S. military officials say is an attempt to prove its relevance after years of economic decline and retrenchment.
Independent U.S. military analysts see the increased Russian submarine patrols as a legitimate challenge to the United States and NATO. Even short of tensions, there is the possibility of accidents and miscalculations. But whatever the threat, the Pentagon is also using the stepped-up Russian patrols as another argument for bigger budgets for submarines and anti-submarine warfare.
U.S. naval officials say that in the short term, the growing number of Russian submarines, with their ability to shadow Western vessels and European coastlines, will require more ships, planes and subs to monitor them. In the long term, the Defense Department has proposed $8.1 billion during the next five years for "undersea capabilities," including nine new Virginia-class attack submarines that can carry up to 40 Tomahawk cruise missiles, more than triple the capacity now.
"We're back to the great powers competition," Adm. John M. Richardson, the chief of naval operations, said in an interview.
Last week, unarmed Russian warplanes repeatedly buzzed a Navy destroyer in the Baltic Sea and at one point came within 30 feet of the warship, U.S. officials said. Last year some of Russia's new diesel submarines launched four cruise missiles at targets in Syria.
Putin's military modernization program also includes new intercontinental ballistic missiles as well as aircraft, tanks and air defense systems.
To be sure, there is hardly parity between the Russian and U.S. submarine fleets. Russia has about 45 attack submarines — about two dozen are nuclear-powered and 20 are diesel — which are designed to sink other submarines or ships, collect intelligence and conduct patrols. But Western naval analysts say that only about half of those are able to deploy at any given time. Most stay closer to home and maintain an operational tempo far below a Cold War peak.
The United States has 53 attack submarines, all nuclear-powered, as well as four other nuclear-powered submarines that carry cruise missiles and Special Operations forces. At any given time, roughly a third of America's attack submarines are at sea, either on patrols or training, with the others undergoing maintenance.
U.S. Navy officials and Western analysts say that American attack submarines, which are made for speed, endurance and stealth to deploy far from U.S. shores, remain superior to their Russian counterparts.
The Pentagon is also developing sophisticated technology to monitor encrypted communications from Russian submarines and new kinds of remotely controlled or autonomous vessels. Members of the NATO alliance, including Britain, Germany and Norway, are at the same time buying or considering buying new submarines in response to the Kremlin's projection of force in the Baltic and Arctic.
But Moscow's recently revised national security and maritime strategies emphasize the need for Russian maritime forces to project power and to have access to the broader Atlantic Ocean as well as the Arctic.
Russian submarines and spy ships now operate near the vital undersea cables that carry almost all global Internet communications, raising concerns among some U.S. military and intelligence officials that the Russians could attack those lines in times of tension or conflict. Russia is also building an undersea unmanned drone capable of carrying a small, tactical nuclear weapon to use against harbors or coastal areas, U.S. military and intelligence analysts said.
And, like the United States, Russia operates larger nuclear-powered submarines that carry long-range nuclear missiles and spend months at a time hiding in the depths of the ocean. Those submarines, although lethal, do not patrol like the attack submarines do, and do not pose the same degree of concern to U.S. naval officials.
Analysts say that Moscow's continued investment in attack submarines is in contrast to the quality of many of Russia's land and air forces that frayed in the post-Cold War era.
"In the Russian naval structure, submarines are the crown jewels for naval combat power," said Magnus Nordenman, director of the Atlantic Council's trans-Atlantic security initiative in Washington. "The U.S. and NATO haven't focused on anti-submarine operations lately, and they've let that skill deteriorate."
That has allowed for a rapid Russian resurgence, Western and U.S. officials say, partly in response to what they say is Russia's fear of being hemmed in.
"I don't think many people understand the visceral way Russia views NATO and the European Union as an existential threat," Ferguson said in an interview.
In Naples, at the headquarters of the U.S. Navy's European operations, including the 6th Fleet, commanders for the first time in decades are having to closely monitor Russian submarine movements through the maritime choke points separating Greenland, Iceland and the United Kingdom, the GIUK Gap, which during the Cold War were crucial to the defense of Europe.
That stretch of ocean, hundreds of miles wide, represented the line that Soviet naval forces would have had to cross to reach the Atlantic and to stop U.S. forces heading across the sea to reinforce America's European allies in time of conflict.
U.S. anti-submarine aircraft were stationed for decades at the Naval Air Station Keflavik in Iceland — in the middle of the gap — but they withdrew in 2006, years after the Cold War was over. The Navy after that relied on P-3 sub-hunter planes rotating periodically through the base.
Now, the Navy is poised to spend about $20 million to upgrade hangars and support sites at Keflavik to handle its new, more advanced P-8A Poseidon maritime patrol aircraft. That money is part of the Pentagon's new $3.4 billion European Reassurance Initiative, a quadrupling of funds from last year to deploy heavy weapons, armored vehicles and other equipment to NATO countries in Central and Eastern Europe, to deter Russian aggression.
Navy officials express concern that more Russian submarine patrols will push out beyond the Atlantic into the Mediterranean and the Black Sea. Russia has one Mediterranean port now, in Tartus, Syria, but Navy officials here say Moscow wants to establish others, perhaps in Cyprus, Egypt or even Libya.
"If you have a Russian nuclear attack submarine wandering around the Med, you want to track it," said Dmitry Gorenburg, a Russian military specialist at the Center for Naval Analyses in Washington.
This month, the Defense Advanced Research Projects Agency christened a 132-foot prototype drone sea craft packed with sensors, the Sea Hunter, which is made with the intention of hunting autonomously for submarines and mines for up to three months at a time.
The allies are also holding half a dozen anti-submarine exercises this year, including a large drill scheduled later this spring called Dynamic Mongoose in the North Sea. The exercise is to include warships and submarines from Britain, France, Germany, the Netherlands, Norway, Poland and the United States.
"We are not quite back in a Cold War," said James G. Stavridis, a retired admiral and the former supreme allied commander of NATO, who is now dean of the Fletcher School of Law and Diplomacy at Tufts University. "But I sure can see one from where we are standing."