The US Commander of Naval Forces in Europe has warned CNN in an interview that Russian submarine activity has reached levels not seen since the Cold War.

Speaking of the spread of submarines, their aggression, buildup, and capabilities, Admiral Mark Ferguson warned that the situation could pose serious problems for NATO in the coming years.

“The submarines that we’re seeing are much more stealthy,” Ferguson told CNN. “We’re seeing (the Russians) have more advanced weapons systems, missile systems that can attack land at long ranges, and we also see their operating proficiency is getting better as they range farther from home waters.”

Ferguson’s concerns echo those raised by NATO Vice Admiral Clive Johnstone, who told IHS Jane’s 360 in February that Russian increase has once again made the North Atlantic a primary area “of concern” to the military alliance.

Additionally, the admiral warned that such levels of Russian activity are nearly unprecedented.

There is now more reported “activity from Russian submarines than we’ve seen since the days of the Cold War,” Johnstone told Jane’s.

And it is not just the number of Russian submarines in a previously uncontested area that has NATO concerned. Although Russia’s navy suffered strongly after the fall of the USSR, Moscow’s submarine forces continued to stay effective.

Playing to its strengths, the Kremlin has successfully continued to focus on its submarine forces through both an effort to modernise and professionalize that segment of the Navy.

US Navy Rear Adm. Dave Johnson said, during a 2014 symposium at the Naval Submarine League, that he was so impressed by the new Russian nuclear guided missile submarine Severodvinsk that he had a model of the submarine built from unclassified data.

“The rest of the world’s undersea capability never stands still,” Johnson said.

Johnstone echoed these comments from Johnson to Jane’s. Russia, in his view, has made “technology leaps that [are] remarkable, and credit to them.”

And retired Admiral James Stavridis, a former NATO supreme allied commander, told CNN that “Russian subs pose an existential threat to U.S. carrier groups,” as the US can no longer maintain “100% awareness of Russian sub activity.”

This sudden Russian expansion is additionally deeply troubling to NATO due to a lack of knowledge about what Moscow’s potential plans may be. This, coupled with Russia’s perceived willingness to interfere in Ukraine and other neighbouring states, has unnerved NATO members.

“Just outside NATO’s territory we face major challenges that could have direct consequences for Norwegian and allied security,” Norwegian Defence Minister Ine Eriksen Soreide writes. Norway has increased military spending by 9.4% for 2016.

The US has also slated an increase in funds for submarines. Over the next five years, the Pentagon is hoping to have $13 billion for submarine research, development, and procurement.

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