Washington (CNN) Nearly invisible to the enemy as it stalks the oceans depths, the USS Hartford, a Los Angeles-class nuclear-powered submarine, provides the US Navy with a lethal combination of stealth and firepower.

Thousands of miles from homeport, the Hartford cruises the Arctic Ocean -- the site of a potential new flashpoint between Russia and the US. CNN saw at first hand how it can launch a two-ton 20-foot-long torpedo capable of destroying an enemy submarine in an instant.

Along with the USS Connecticut fast-attack submarine and the UK Royal Navy's HMS Trenchant, the 6,000-ton Hartford is currently participating in multinational exercises training for its primary mission: to hunt and kill enemy ships and submarines.

The Arctic is the newest and most daunting front in the expanding global conflict between the US and Russia as both nations battle to control nearly 5.5 million square miles of frozen terrain.

But the receding ice is opening new opportunities for oil exploration, potential shipping lanes and -- crucially -- new paths to wage war.

"We are well aware that we are in a great power competition environment and the Arctic is one piece of that," said Navy Rear Adm. James Pitts, commander of the Undersea Warfighting Development Center. "All the more reason why we the Navy are practicing up here and doing exercises to make sure that we can operate effectively."

But while the US Navy regularly conducts submarine training drills -- often with key allies -- this five-week operation dubbed "ICEX" is unique, as it takes place in one of the harshest environments in the world -- under the Arctic ice.

It's a region where even surfacing requires enormous power and skill, but the drills "provide the US submarine force and partners from the British navy an opportunity to test combat and weapons systems, sonar systems, communications and navigation systems in a challenging operational environment," Navy Cmdr. Corey B. Barker said in a Pentagon news release

"From a military, geographic, and scientific perspective, the Arctic Ocean is truly unique, and remains one of the most challenging ocean environments on earth," Pitts said.

The unique acoustic undersea environment is further compounded by the presence of a contoured, reflective ice canopy when submerged, according to the Defense Department.

"Our submarine forces are capable of operating here just as we operate along our East Coast and throughout the world," the Hartford's Cmdr. Matthew Fanning told CNN.

These types of drills show "we are capable of doing it and willing to come up here and conduct operations," he added.

Russia and China are two powers trying to catch up to US submarine capability, Pitts said.

Specifically, Russia has invested heavily in developing its own underwater stealth capabilities in recent years and their submarine technology is approaching the level of the US fleet, much like the peer-to-peer comparison seen during the Cold War, a congressional aide familiar with the issue recently told CNN.

An emerging submarine rivalry has added new urgency to this year's ICEX exercises. A British submarine joined the maneuvers for the first time in a decade and US forces are refocusing on a Cold War-style mission.

According to Fanning, US submarine forces have shifted their focus away from the post-9/11 counter terrorism mindset and back toward an emphasis on lethality -- or leveraging offensive weaponry, like a torpedo, against a threat.

And the ability to wield the submarine as an offensive weapon is something Fanning said he teaches to every member of his watch team, not just the highest-ranking officers.

Operating under the Arctic presents its own unique challenges as submarines are unable to rely on access to GPS navigation and have limited communications.

Crews also face danger from below and above as ice keels as long as 150 feet extend down from the ice sheet.

However, the biggest challenge of navigating in the Arctic still comes from Russia.

In addition to developing quieter, more deadly submarines of their own, the Russian military has assembled an arc of steel along its Arctic coast made up of dozens of military bases, ports and airfields.

"We know that in every case they are trying to get faster and better at what they do and integrating technology into their platforms," Commodore Ollie Lewis, Commander of Submarine Squadron 12 told CNN.

"It's really set them on a ramp to where if we don't continue to do the same, we'll find ourselves in a place of falling behind," he said.

Photos: U.S. Navy's submarine fleet The USS Michigan, an Ohio-class guided-missile submarine, arrives in Busan, South Korea, for a routine port visit in December 2010. Click through the gallery to see some of the other subs in the U.S. Navy's fleet. Hide Caption 1 of 8 Photos: U.S. Navy's submarine fleet A dolphin swims in front of the Virginia-class attack submarine USS John Warner during its sea trials in May 2015. Virginia-class subs, displacing 7,800 tons and at 377 feet long, "are designed to seek and destroy enemy submarines and surface ships; project power ashore with Tomahawk cruise missiles and special operation forces (SOF); carry out inntelligence, surveillance, and reconnaissance (ISR) missions; support battle group operations; and engage in mine warfare," according to the Navy. Hide Caption 2 of 8 Photos: U.S. Navy's submarine fleet The Ohio-class guided-missile submarine USS Georgia (SSGN 729) departs Naval Submarine Base Kings Bay to conduct routine operations in October 2015. Hide Caption 3 of 8 Photos: U.S. Navy's submarine fleet The USS Seawolf, shown here in support of European operations in June 2015, is the lead vessel in the three-boat Seawolf class. The Seawolf and the USS Connecticut, the second boat in the class, displace 9,138 tons and are 353 feet long. Click to the next slide to learn more about the third sub in the class, the USS Jimmy Carter. Hide Caption 4 of 8 Photos: U.S. Navy's submarine fleet The Seawolf-class attack submarine USS Jimmy Carter is moored in a Washington state facility that reduces a ship's electromagnetic signature in 2006. The Jimmy Carter is 100 feet longer than the first two subs in its class. The extra space is for a "multimission platform," the Navy says. "This hull section provides for additional payloads to accommodate advanced technology used to carry out classified research and development and for enhanced warfighting capabilities." Hide Caption 5 of 8 Photos: U.S. Navy's submarine fleet The U.S. Navy has more than a dozen ballistic missile submarines, also called boomers, in service. The boomers, 560 feet long, can carry 24 nuclear-armed Trident II ballistic missiles and serve as nuclear deterrents. Here, the Ohio-class ballistic-missile submarine USS West Virginia departs a naval shipyard in 2013. Hide Caption 6 of 8 Photos: U.S. Navy's submarine fleet The Ohio-class guided-missile submarine USS Ohio transits Puget Sound, Washington, in June 2015. The Ohio and three other guided-missile subs -- USS Florida, USS Michigan and USS Georgia -- were originally built and deployed as ballistic-missile subs, but were converted to guided-missile platforms beginning in 2002 after the Navy concluded it had a surplus of the boomers. Hide Caption 7 of 8 Photos: U.S. Navy's submarine fleet The Los Angeles-class attack submarine USS Hampton surfaces through Arctic ice in March 2014. The Los Angeles-class is the biggest in the Navy's sub fleet, with a few dozen in commission. These subs displace 6,900 tons and are 360 feet long. The class was introduced in 1976. Hide Caption 8 of 8

For the US Navy, maintaining that undersea advantage means building more submarines and adding more capabilities.

By most accounts, the US still maintains the most capable submarine fleet in the world -- the Hartford is virtually invisible and silent to its enemies allowing it to strike without warning and hit targets both above and below the surface.

But despite President Donald Trump's request for additional defense spending, years of budget cuts and continuing resolutions have had a severe impact on the Navy's maintenance and shipbuilding efforts.

In addition to it's 42 active Los Angeles-class submarines, the Navy plans to build 30 Virginia-class submarines and replace its 14 aging Ohio-class boats with 12 Columbia-class submarines, the first of which is expected in fiscal year 2021.