Exclusive to ABC News: Inside the US ballistic missile submarine in South Korea

BUSAN, South Korea — The arrival this week of a US Navy submarine carrying nuclear weapons in Busan, South Korea, marked the first time a submarine capable of carrying up to 20 nuclear-tipped ballistic missiles made a port of call in South Korea.

The rare public visit is intended to demonstrate US security commitments to South Korea and to deter North Korea.

ABC News Chief Global Affairs Correspondent Martha Raddatz was granted exclusive access to the USS Kentucky in Busan, South Korea, on Thursday, becoming the only U.S. journalist allowed to visit the submarine during its port of call in South Korea.

Busan, South Korea’s largest port, is located at the southeasternmost point of the Korean peninsula and more than 200 miles south of the DMZ (demilitarized zone) that serves as the border with North Korea.

Over two football fields long, the USS Kentucky (SSBN 737) is one of 14 U.S. Navy Ohio-class submarines capable of launching 20 Trident 2 D5 missiles, each armed with multiple targeted warheads capable of hitting targets up to 4,000 miles away.

As is standard practice, the US Navy does not say whether nuclear weapons are on board its Ohio-class submarines.

The deployment of these submarines is highly classified and it is extremely rare for them to call at a port of call, but the Kentucky’s visit realized a commitment made in April by President Joe Biden and South Korean President Yoon Suk Yeol that a US ballistic missile submarine would visit South Korea in a demonstration of US security commitments.

“It represents our long-standing relationship with the Republic of Korea, our commitment to security and our comprehensive deterrence. It reassures our allies and deters potential adversaries,” Vice Admiral Chris Cavanaugh, director of the US Pacific Fleet’s Naval Headquarters, told Raddatz in an interview aboard the USS Kentucky.

Shortly after the submarine’s arrival in Busan on Tuesday, North Korea launched two short-range ballistic missiles in an apparent response to the rare port of call. On Thursday, North Korean Defense Minister Kang Sun-nam warned that the submarine’s visit posed a threat to North Korea and could fall under that country’s terms of use of nuclear weapons.

Tensions with North Korea became apparent this week when a US soldier, Army Pvt. Travis King, fired across the Panmunjon DMZ into North Korea, where he is now believed to be in the custody of North Korean authorities.

Cavanaugh said Ohio-class submarines like the Kentucky deter the possibility of nuclear conflict.

“I have great confidence in our own nuclear deterrent. Again, any adversary who would consider an attack knows that we have a huge response capability that is untargeted and localized by them,” he told Raddatz.

That nuclear deterrent is also intended to allay concerns about South Korea’s security.

“We’re doing a whole host of things to assure them of our comprehensive deterrence, which means we’re not taking any capabilities off the table when it comes to defending our allies,” Cavanaugh said.

South Korean President Yoon and other senior Korean and US military leaders visited the submarine on Wednesday.

Yoon said the visit “demonstrates the routine deployment of strategic resources by the US and the will of the two countries to defend the ability to conduct comprehensive deterrence.”

“This means that North Korea cannot even dream of a nuclear provocation, and it serves as a clear warning to North Korea that such a provocation would mean the end of the regime,” Yoon said.

The approximately 150 sailors aboard the USS Kentucky are commanded by Cmdr. Lee “Randy” Fike, telling Fife, told Raddatz that his crew was very proud of serving aboard the first ballistic missile submarine to visit South Korea since 1981.

Day-to-day life aboard Ohio-class submarines during months of deployment involves a great deal of training for the submarine’s crew and officers, especially in the submarine’s missile control center, where the crew simulates launch procedures for the ICBMs it carries.

“It’s a big focus of what we do day in and day out, training to make sure we’re ready to demonstrate that we have a safe, secure and effective nuclear deterrent,” Fike said. “And I hope you never have to use it. Absolutely.”

The responsibility of being a vital part of America’s nuclear triad is not lost on the crew, some of whom have witnessed firsthand the power of a Trident missile test launch aboard a submarine.

“It’s very, very sobering,” Commander. Fike told Raddatz. “We go through these training simulations all the time, but nothing can replicate the feeling that comes when a 100,000 pound D-5 missile leaves a submarine.”

Because ports of call are so rare during submarine patrols, Fike noted that as an experienced submariner, visiting the Busan was his very first port of call during a deployment.

“The seriousness of what we’ve been allowed to do and work with our allies in the Republic of Korea, it’s absolutely amazing,” Fike said.

“For most of my crew members, this is the first time they set foot on a foreign land,” said Fike. “So it’s a great opportunity for us. And the host country has been absolutely welcoming.”

Missile Technician 2 Ryan Shirley, 24, was allowed to come ashore and enjoyed a visit to a local mall in South Korea.

“It’s a different change of scenery and how they work there in South Korea,” Shirley told Raddatz.

But the history of the moment did not escape Shirley, who admitted to thinking about the upcoming visit for days.

“I think it’s really good,” said Nichols.

Petty Officer 2nd Class Tyler Forner of Savannah, Georgia, who reenlisted in the Navy Thursday after serving three years aboard the USS Kentucky.

Forner labeled the port of call “historic” and “a cool experience” for the U.S. Navy’s submarine force to make a port of call to Busan.

It is unclear how long the USS Kentucky will remain in the port of Busan.