NATO officials have repeatedly warned about the rising threat posed by Russian submarines.

A major concern is those subs' land-attack capabilities, which now allow them to strike deep in Europe.

NATO navies have ramped up anti-submarine-warfare tactics, but those land-attack missiles may mean ASW needs to change.

NATO naval officials have repeatedly warned about Russia's submarines — a force they say is more sophisticated and active.

US Navy officials have said several times that Russian subs are doing more now than at any time since the Cold War, though intelligence estimates from that time indicate they're still far below Cold War peaks.

They're also worried about where those subs are going. US officials have suggested more than once that Russian subs are lurking around vital undersea cables. (The US did something similar during the Cold War.)

But the most significant capability Russian subs have added may be what they can do on land.

Long-range Kalibr cruise missiles are launched by a Russian Navy ship in the eastern Mediterranean AP/Russian Defense Ministry Press Service

Asked about the best example of growth by Russia's submarines, Adm. James Foggo, the head of US Naval Forces in Europe and Africa, pointed to their missiles, which offer relatively newfound land-attack capability.

"The Kalibr class cruise missile, for example, has been launched from coastal-defense systems, long-range aircraft, and submarines off the coast of Syria," Foggo said on the latest edition of his command's podcast, "On the Horizon."

"They've shown the capability to be able to reach pretty much all the capitals in Europe from any of the bodies of water that surround Europe," he added.

The Kalibr family of missiles — which includes anti-ship, land-attack, and anti-submarine variants — has been around since the 1990s.

Ranges of Russia's Kalibr missiles when fired from seas around Europe. Light red circles are the land-attack version. Dark red circles indicate the anti-ship version CSIS Missile Defense Project

The land-attack version can be fired from subs and surface ships and can carry a 1,000-pound warhead to targets between 930 miles and 1,200 miles away, according to CSIS' Missile Defense Project. It is said to fly 65 feet above the sea and at 164 to 492 feet over land.

After the first strikes in Syria, the Russian Defense Ministry said the Kalibr was accurate to "a few meters" — giving them a capability not unlike the US's Tomahawk cruise missiles.

In 2011, the US Office of Naval Intelligence quoted a Russian defense industry official as saying Moscow planned to put the Kalibr on all new nuclear and non-nuclear subs, frigates, and larger ships and that it was likely to be retrofitted on older vessels.

But the system wasn't used in combat until 2015.

In October that year, Russian warships in the Caspian Sea fired 26 Kalibr missiles at ISIS targets in Syria. The submarine Veliky Novgorod fired three Kalibrs from the eastern Mediterranean at ISIS targets in eastern Syria later that month, and that December a Russian sub fired four Kalibrs while en route to its home port on the Black Sea.

' They’re messaging us'

A Russian Navy ship launches Kalibr cruise missiles from the Caspian sea at targets over 1000 miles away in Syria. IN THE NOW via Youtube

Russian surface ships and subs have fired Kalibr missiles at targets in Syria numerous times since. But their use may be more about sending a message to Western foes than gaining an edge in Syria.

"There’s no operational or tactical requirement to do it," NORTHCOM Commander Adm. William Gortney told Congress in early 2016. "They’re messaging us that they have this capability."

Russia has used "Syria as a bit of a test bed for showing off its new submarine capabilities and the ability to shoot cruise missiles from submarines," Magnus Nordenman, the director of the Transatlantic Security Initiative at the Atlantic Council, told Business Insider earlier this year.

A 2015 Office of Naval Intelligence report cited by Jane's noted that the "Kalibr provides even modest platforms … with significant offensive capability and, with the use of the land attack missile, all platforms have a significant ability to hold distant fixed ground targets at risk using conventional warheads."

A long-range Kalibr cruise missile is launched from the Krasnodar submarine in the Mediterranean, in an image provided by the Russian Defense Ministry press service on May 31, 2017. (Russian Defence Ministry Press Service photo via AP)

"The proliferation of this capability within the new Russian Navy is profoundly changing its ability to deter, [or to] threaten or destroy adversary targets," the report said.

While Russia's submarine force is still smaller than its Soviet predecessor, that cruise-missile capability has led some to argue NATO needs to look farther north, beyond the Greenland-Iceland-UK Gap that was a chokepoint for Russian submarines entering the Atlantic during the Cold War.

Today's Russian subs "don't have to go very far out in order to hit ports and airports and command and control centers in Europe, so they don't have to approach the GIUK Gap," Nordenman said in a recent interview. "In that sense the GIUK Gap is not as important as it used to be."

'We need to deny that edge'

A Dutch helicopter participates in NATO's Dynamic Mongoose anti-submarine exercise in the North Sea off the coast of Norway, May 4, 2015. REUTERS/Marit Hommedal/NTB Scanpix

Foggo said US submarines still have the edge, but the subs Russia can deploy "are perhaps some of the most silent and lethal in the world."

Concerns about land-attack missiles now mix with NATO's concern about bringing reinforcements and supplies from the US to Europe during a conflict.

"That's why Russian submarines are a concern," Nordenman said earlier this year. "One, because they can obviously sink ships and so on, but related, you can use cruise missiles to shoot at ports and airfields and so on."

"We know that Russian submarines are in the Atlantic, testing our defenses, confronting out command of the seas, and preparing a very complex underwater battle space to try to give them the edge in any future conflict," Foggo said. "We need to deny that edge."

US Navy crew members on board a P-8A Poseidon assisting in search and rescue operations for Malaysia Airlines flight MH370 in the in the Indian Ocean, March 16, 2014. US Navy

This has led to more emphasis on anti-submarine warfare, a facet of naval combat that NATO forces focused on less after the Cold War.

The US Navy has asked for more money to buy sonobuoys, supplies of which fell critically short after an "unexpected high anti-submarine warfare operational tempo in 2017." NATO members also plan to buy more US-made P-8A Poseidons, widely considered to be the best sub-hunting aircraft on the market.

But the Kalibr's anti-ship capability has also raises questions about whether ASW itself needs to change.

At a conference in early 2017, Lt. Cmdr. Ian Varley, deputy commander of the Royal Navy's Merlin helicopter force, said anti-ship missiles were pushing ASW away from "traditional … close-in, cloak and-dagger fighting" to situations where an enemy submarine "sits 200 miles away and launches a missile at you."

"That becomes an air war," he said. "We need to stop it becoming an air war. We need to be able to have the ability to defend against that."