In the dark depths of the Pacific, US submarines patrol with an eye fixed firmly on China

Honolulu, Hawaii CNN --

Jeff Jablon, Rear Admiral of the US Navy, is clear about the two greatest challenges facing his team.

He explained this on the USS Mississippi - a nuclear-powered fast-attack sub belonging to the US Pacific Fleet.

The Soviet Union, and now Russia, was our equal adversary in terms of nuclear capability. Now we're facing China which has modernized and expanded their nuclear capability.

The Virginia-class sub had left its Pearl Harbor base in Hawaii earlier that day and was on a routine mission when it slid below the waves to the largest ocean of the world.

Around 130 sailors worked at various stations on the ship, performing a variety of tasks.

More than a dozen sailors worked in the control room. Some were looking for obstructions on sonar while others were tasked with navigating the deep.

Engineers manned the lower levels to ensure that the water and hydraulic system was working properly.

The crew members describe a cramped, claustrophobic job, with long periods of time at sea, and close relationships that are almost family-like.

Jack O'Brien (22), a machinist in Massachusetts, said of his fellow workers: "I see them everyday, work with them daily, and sleep right next to one another."

"Even when we are in port, our work continues from sunup to sunset."

AUKUS sub deal

A CNN crew had exclusive access to one of the 49 fast-attack subs that Jablon claimed to be in the US Fleet, the USS Mississippi. The crew witnessed how Washington was stepping up its preparations to prevent a possible conflict in the area.

This month, the United States announced a deal with the United Kingdom, Australia and Canada to build a nuclear submarine that would allow the three countries greater cooperation to counter China's rapid expansion of its military.

The so-called AUKUS agreement will see Australia buy three Virginia class submarines in the early 30s, subject to congressional approval.

China has criticized the agreement and accused the three powers that they are engaging in a 'Cold War Mentality' which will make the world safer.

The US Defense Department announced that the USS Mississippi visited Perth in November and conducted training sessions with Royal Australian Navy members.

China's increasing military ambitions in the Western Pacific, and in the South China Sea have been alarming to the US and its allies.

Beijing's ruling Communist Party also refuses to rule out using force to capture Taiwan, a selfgoverning democracy with 23.5 million people that it claims is a part its territory despite never having ruled it.

A CNN crew was aboard a US Navy surveillance jet in international waters of the South China Sea when a Chinese fighter plane flew close to intercept it last month.

'The National Security Strategy states that the PRC (People's Republic of China) is our leading threat and Russia is a serious threat to our nation,' said Rear Adm. Jablon commander of Submarine Force of the US Pacific Fleet.

Jablon said that the majority of our submarines are now in the Pacific. "At this time, approximately 60% of our operational submarines are in the Pacific due to these challenges."

Experts say that despite the advancements made by the Chinese, the US has an advantage in undersea war.

Carl Schuster said that the United States has unchallenged supremacy over China in the area of submarines. He is a retired US Navy Captain and former director at the Joint Intelligence Center, Hawaii, for the US Pacific Command.

Schuster stated that 'they are the only stealth platforms with the power to strike and the survivability necessary to combat the PLA Navy surface and subsurface forces'.

The power of the formidable

Like all US Navy subs, the Mississippi is powered by nuclear power, giving it an essentially unlimited range and deployment time. It only needs to call into port to get provisions for its crew.

Jablon said: "All we need are enough foods for each individual, and we can go around the world without replenishing."

The Navy's 14 ballistic-missile submarines are larger vessels, often called 'boomers'.

The USS Mississippi still has a formidable arsenal. Its class is equipped with Tomahawk cruise-missiles, which can reach targets 1,600 km away and up to 1,000 miles. Torpedoes are also available to attack enemies on the surface or beneath the water.

Edward Perry, USS Mississippi's commanding officer, stated that the ship can carry 25 Mark-48 heavyweight torpedoes when fully loaded. These are advanced torpedoes capable of striking enemies on land or under the sea.

Jablon stated that the US submarine force is increasingly making its presence known in the public as well as to adversaries because it has a deterrent impact.

Jablon stated, 'During the Cold War we used to be called the silent service, and (we) didn't let anyone know where our operations were.

"In the submarine force of today, we work extensively with other services in the United States and our allies." The adversary will know that we are capable of operating in international waters around the globe.

China has massively expanded its navy over the past few decades. However, it is still far behind the US in terms of nuclear-powered subs, which Beijing wants to change.

According to a report by the Congressional Research Service on China's Naval Modernization, between 2020 and 2030, the number of ballistic missile and nuclear-powered submarines in China will more than double.

Meanwhile, the PLA Navy is expected to maintain 44 diesel-powered/air-independent powered attack submarines, according to the US military.

Mike Sweeney a PhD student from George Mason University notes in Proceedings of the US Naval Institute a problem with numbers and scope for US Navy submarines.

He claims that US sub technology is superior to China's but that it "may simply not have sufficient numbers" in any conflict with China.

Jablon, rear admiral Jablon, provided more information on the dispersal of US Navy submarines.

He said that 25 of the 49 attack submarines in the fleet are stationed on the Pacific. Jablon refused to give specifics, but he did say that some of the subs are not available for maintenance or other purposes.

According to some analysts, this could include up to two thirds of the fleet.

Sweeney, in Proceedings, wrote: 'An older rule of thumb holds that two vessels are needed for every vessel operational -- one for preparing to deploy and the second for standing down from previous operations.'

The PLA Navy has an advantage over China in terms of the number of submarines it can deploy in the Indo-Pacific.

The US Congressional Budget Office has also released numbers that indicate another problem for US attack subs - by 2028 the fleet will be down to 46 boats, but new building programs are expected to kick in to bring it up to 69 boats.

Last month, US Navy Sec. Carlos Del Toro said to a House Appropriations Subcommittee the construction of new Virginia class submarines were'significantly' behind schedule. He stated that the subs are being built at a pace of 1.4 per year, which is well behind the two subs planned each year.

Far from your loved ones

Submariners can have a unique life compared to other branches of military.

The crew of the USS Mississippi must live in an enclosed space with limited communication to the outside world because the submarine can stay submerged for long periods.

Ship commander Perry explains that the crew is divided into three shifts in order to keep the warship manned 24 hours per day.

On a nuclear sub, the daily routine is fairly standard. Crew members are on duty for 8 hours a day and then have to spend another 8 hours studying, cleaning, or socializing before going to bed.

Perry, a 19-year veteran of the US Navy, said: "I believe the greatest strategic asset for the United States is its people."

They're well-trained, well-educated, have a lot experience and are patriotic. It's because of this that I believe few people are able to replicate a vessel such as this when it's put out at sea.

Steven Wong, 26, an electronics technician from California said that he was initially shocked by the small space aboard a nuclear sub.

Wong is in charge of operating the nuclear reactor that provides electricity and power.

It is difficult to stay in touch with family members when you are in the middle of the ocean.

Wong's wife, who lives in Hawaii, said that the only way they could really communicate was through email. Every day, I go to my unclassified PC to check my email. It's always a thrill to me when I see an unread message.