US-South Korea nuclear submarine deal: What does it mean?

The South Korean government has announced that it has finalized an agreement to build nuclear-powered submarines in partnership with the United States.

The United States approved the “attack submarines” and agreed to cooperate on fuel supplies, according to a fact sheet released by the White House on Thursday.

The agreement marks a significant step in South Korea’s relations with the United States and comes amid a period of rising tensions on the Korean Peninsula: with nuclear-armed North Korea and an expansionist China to the west.

Here’s what you need to know about the deal.

The agreement between the United States and South Korea comes as leaders of both countries reached a broad trade agreement early last month that would reduce reciprocal tariffs from 25% to 15%.

US President Donald Trump had imposed a 25% tariff rate on Seoul earlier this year, which his counterpart Lee Jae Myung managed to negotiate down to 15%, after Seoul said it would invest $350bn (£265bn) in the US, including $200bn in cash investments and $150bn in construction. naval.

In a White House statement released Thursday, the United States said it had “given approval for the Republic of Korea to construct nuclear-powered attack submarines… [and would] work closely to advance the requirements of this project, including pathways to fuel.”

In an earlier post on his social media platform Truth Social, Trump had said the ships would be built at a shipyard in Philadelphia run by South Korean conglomerate Hanwha.

Currently, only six countries possess strategic nuclear-powered submarines: the United States, China, Russia, the United Kingdom, France and India.

South Korea already owns about 20 submarines, but they are all diesel-powered and therefore need to surface much more frequently. Nuclear submarines can also operate at greater distances and faster.

“I have given them approval to build a nuclear-powered submarine, instead of the antiquated and much less agile diesel-powered submarines they have now,” Trump had written in Truth Social.

South Korea is a powerhouse when it comes to civil nuclear energy. It had a nuclear weapons program in the 1970s but abandoned it after pressure from the United States.

And that is why its ability to enrich or reprocess uranium is limited by the United States, since it depends entirely on imports.

The latest ship program is aimed at countering North Korea, which recently revealed it was pursuing its own nuclear submarine program.

President Lee had told Trump at the APEC summit last month that South Korea needed them for that express purpose.

In a television interview last week, Ahn Gyu-back, South Korea’s Defense Minister, said nuclear submarines would be a “proud achievement” for South Korea and a huge leap in strengthening the country’s defense against the North.

The stealth of nuclear submarines would keep North Korean leader Kim Jong Un “up at night,” he added.

North Korea has also been pursuing a nuclear submarine program, possibly with help from Russia, according to South Korean officials.

In March 2025, North Korea revealed photographs of what it claimed was a nuclear-powered submarine under construction, showing Kim visiting the shipyard.

Pyongyang is expected to have the submarines in the coming years.

North Korea is also estimated to have an arsenal of approximately 50 nuclear weapons, as part of its broader nuclear weapons program.

Jo Bee-yun, a researcher at the Sejong Institute, suggested that Seoul’s acquisition of nuclear submarines will help it keep up with East Asia’s growing arms race.

“North Korea’s nuclear weapon is an established fact,” he told the BBC. “[South Korea acquiring] “Nuclear submarines are just one step in the broader trend of rising tensions.”

It is unclear how much nuclear-powered submarines will contribute to South Korea’s defense capabilities, and while they are very expensive, they do not entirely change the balance of power on the Korean peninsula, according to some experts.

Yang Uk, a researcher at the Asan Institute for Policy Studies, told the BBC that the main purpose of nuclear submarines is to reassure South Korean voters that their government is responding to the North Korean nuclear threat.

“South Korea cannot develop its own nuclear weapons to counter North Korea’s,” Dr. Yang said. “What can they do? Place nuclear submarines.”

However, Dr. Yang believes North Korea might enjoy the change because it strengthens its rationale for retaining nuclear weapons, meaning it will be harder to demand that Pyongyang give up its nuclear arsenal.

However, Jo emphasized the strategic advantage South Korea can gain from the new submarine deal, describing it as a “major change” that “means South Korea is now a regional player.”

“The best feature of a nuclear submarine is its speed,” he said. “Now it can go fast and far and South Korea can operate together with more countries.”

For Washington, support for South Korea’s nuclear-powered submarine program is likely aimed at putting pressure on both North Korea and China.

“Trump has put the burden of defense spending on the backs of South Korea,” Dr. Yang explained. “South Korea will greatly expand its defense budget. They will act as proxies for the United States to pressure China and North Korea.”

The United States and China have long competed for strategic influence in South Korea, leaving Seoul walking a geopolitical tightrope. More recently, China has been increasing its naval activity near South Korea’s maritime border, a move similar to those seen in the South China Sea.

Beijing must be “furious” about South Korea’s nuclear submarine deal with the United States, Dr. Yang said.

Following the deal’s announcement, China’s ambassador to South Korea, Dai Bing, said he hoped South Korea would “approach this issue prudently, taking into account the concerns of all parties.”

Dai also added that Beijing was engaging with Seoul on the matter through diplomatic channels and emphasized that “the (security) situation on the Korean Peninsula and in the region remains complex and sensitive.”

Although President Trump said the submarines would be built in Philadelphia and bring jobs to the United States, South Korean officials have maintained that they should be built locally, where existing facilities can deliver them on a much shorter timeline.

South Korea’s Prime Minister Kim Min-seok himself had said during a parliamentary hearing that the South Korean-owned shipyard in Philadelphia “did not have the capacity” to build such ships, according to reports.

Hanwha, owner of the shipyard, has not yet commented on the matter.

But now that an agreement has been reached, the next step is to adjust the nuclear deal between the two countries, allowing the United States to provide nuclear fuel and setting a limit on its military use.