Russia's powerful Northern Fleet just got the first of a new class of submarines that has the US Navy worried

• In May, Russia's navy finally commissioned the Kazan, a new and completely modern guided-missile sub.
• Kazan is the culmination of more than a decade of effort, and it is a marked improvement over its predecessor, which already had NATO commanders worried.

On May 7, the Russian Navy finally commissioned the Kazan, its first Yasen-M-class nuclear-powered guided missile submarine (SSGN).

Kazan is the lead boat of a subclass descended from the Yasen class, the first of which, Severodvinsk, was commissioned in 2013.

Kazan is the culmination of more than a decade of effort to field a new and completely modern SSGN, and it is a marked improvement in nearly every respect over its predecessor, which already had US commanders and their NATO allies worried.

Severodvinsk and Kazan represent a new chapter for Russia's submarine force - long considered the most important part of the Russian Navy.

The Yasen-class

The Yasen-M-class has an interesting history. Although it is believed to be Russia's most advanced and expensive submarine class ever, the original Yasen design comes from the latter days of the Cold War.

Since its start, the Yasen program has been beset by delays and setbacks. The collapse of the USSR was followed by extensive budget cuts for the Russian Navy and the erosion of critical shipbuilding infrastructure and expertise.

Severodvinsk was laid down in 1993 but did not enter service until 2013. Construction of Kazan didn't begin until 2009.

At 456 feet long, the Severodvinsk has 10 torpedo tubes located near the central post instead of the bow (a first for Russian submarines) and eight vertical launch tubes, each capable of holding multiple missiles.

Severodvinsk is also armed with either 32 P-800 Oniks or 40 3M-14 Kalibr missiles, or a combination of both. Both missiles have variants that can be used to strike land targets or enemy warships.

The Kalibr, which entered service in 2015, is particularly threatening, as its range of over 1,500 miles gives the Russian Navy the ability to conduct long-range strike missions with conventional weapons for the first time.

The Severodvinsk also has much more advanced quieting technology than its predecessors, and has already proven able to avoid detection.

In 2019, Pentagon officials told "60 Minutes" that the sub had sailed into the Atlantic in 2018 and "for weeks" evaded all efforts to find it.

The Yasen-M

Because Kazan took so much longer to develop, it could be loaded with advanced technology developed in the last few years. Its overall design was also refined, placing it in a distinct subclass.

"You really have a fundamentally new submarine in many respects," Jeffrey Edmonds, a research scientist at the Center for Naval Analysis, told Insider.

Though it is slightly smaller than the Severodvinsk, the Yasen-M class features new control systems, new quieting technology, new sensor suites, new personnel-rescue systems, new damage-control systems, and even an updated nuclear reactor designed to make less noise.

Although Yasen-M only has eight torpedo tubes compared to Severodvinsk's 10, it can carry the same kind and number of missiles.

There are also reports that Kazan will be armed with the Zircon, the Russian hypersonic missile reportedly capable of reaching speeds between Mach 6 and Mach 8. Final testing of the Zircon is expected to begin in June.

At first glance, Yasens may appear less threatening than Russia's nuclear-powered ballistic-missile submarines, particularly those of the new Borei-class.

But those ballistic-missile boats are more predictable; they are covered by agreements like the New START Treaty, and their nuclear arsenals would likely only be used in absolute worst-case scenarios.

The Yasens, on the other hand, carry advanced conventional weaponry capable of striking targets deep inland. Combined with their stealth capabilities and their ability to be almost anywhere in any ocean, the threat of the Yasens is hard to understate.

"The Severodvinsk is [meant] for long-range patrols in the ocean," Edmonds said. "During wartime we'd be worried about Severodvinsk submarines sitting off the East Coast or the Pacific Coast."

'No longer a sanctuary'

The US Navy has repeatedly sounded the alarm over increased Russian Navy capabilities and activities.

Vice Adm. Andrew Lewis, the commander of the 2nd Fleet, warned last year that "our ships can no longer expect to operate in a safe haven on the East Coast or merely cross the Atlantic unhindered."

Vice Adm. Daryl L. Caudle, commander of Naval Submarine Forces, echoed those concerns in September, saying that "it's pretty well known now that our homeland is no longer a sanctuary, so we have to be prepared here to conduct high-end combat operations in local waters."

Those concerns stem mostly from improvements in Russia's submarine fleet, especially the Severodvinsk and Kazan.

With Kazan completed and commissioned and the Yasen-M design finalized, it is believed that Kazan's sister-boats will take less time to construct.

The second Yasen-M, Novosibirsk, was launched in December 2019 and is expected to be delivered to the Navy by the end of this year. The third boat, Krasnoyarsk, will be launched in August and is expected to be commissioned in late 2022.

If Russia sticks to its timetable, five more Yasen-Ms will join the fleet by the end of the decade.

Severodvinsk and Kazan are part of Russia's Northern Fleet based in Severomorsk, while Novosibirsk and Krasnoyarsk will join the Pacific Fleet.

In all, four Yasen-Ms and the Severodvinsk will be in the Northern Fleet, with the other four in the Pacific Fleet. Russia does not deploy any of its nuclear submarines to the Baltic or Black Sea fleets because they do not have easy access to the open ocean.

With more Yasens in service, Russia's strategic deterrence capabilities are markedly enhanced.

"It's something that can bring the fight to the continental US," Edmonds told Insider. "There is a certain conventional non-nuclear deterrent aspect to the Severodvinsk, and I think that plays into the larger strategic framework that the Russians operate in."

"It's just a formidable undersea platform," Edmonds said.