South Korea has confirmed a landmark defence agreement with the United States that will allow Seoul to begin building nuclear-powered submarines — a major shift in its military capabilities and strategic posture.
According to a White House fact sheet released on Thursday, Washington has formally approved South Korea’s plan to develop nuclear-powered attack submarines and will cooperate in securing the necessary fuel. The deal comes at a time of rising tension in East Asia, with North Korea expanding its nuclear ambitions and China projecting greater military influence in the region.
Key details of the agreement
The submarine deal follows a wider trade understanding reached last month, where both countries agreed to reduce tariffs from 25% to 15%. Earlier this year, President Donald Trump imposed a 25% tariff on South Korean exports, but President Lee Jae Myung negotiated a reduction after pledging a massive $350bn investment into the US economy — $200bn in cash and $150bn in shipbuilding.
Thursday’s announcement marks the first time the US has approved such a project for South Korea. In a Truth Social post, Trump said that the submarines would be constructed at a Philadelphia shipyard owned by Korean conglomerate Hanwha.
Currently, only six countries operate nuclear-powered submarines: the US, China, Russia, the UK, France and India. South Korea’s fleet of around 20 submarines are all diesel-powered, meaning they must surface frequently. Nuclear submarines can travel much faster and remain submerged for long periods.
“I have given them approval to build a nuclear-powered submarine,” Trump wrote, calling it a significant upgrade from the diesel-powered vessels South Korea relies on today.
Although South Korea leads globally in civilian nuclear energy, its military nuclear activities remain tightly restricted under US agreements, meaning Seoul depends entirely on foreign fuel sources.
Why Seoul wants nuclear submarines
South Korea sees the new programme as essential to countering North Korea’s expanding arsenal. Pyongyang recently revealed efforts to develop its own nuclear-powered submarine, which it displayed in March 2025 when Kim Jong Un visited a shipyard for inspection.
Defence Minister Ahn Gyu-back described South Korea’s upcoming nuclear submarines as a “proud achievement” and a major boost to national security. Their stealth capabilities, he said, would “keep Kim Jong Un awake at night.”
North Korea, meanwhile, is estimated to possess around 50 nuclear warheads — part of a broader weapons programme that has accelerated in recent years. Analysts believe Seoul’s acquisition of nuclear submarines is part of a broader arms race unfolding across East Asia.
Will this raise tensions?
Experts are divided. While nuclear submarines are powerful assets, some analysts argue that the move will not dramatically alter the military balance on the Korean Peninsula. Instead, they see it as a political signal to reassure the South Korean public.
“South Korea cannot build its own nuclear weapons,” said Yang Uk of the Asan Institute for Policy Studies. “Deploying nuclear submarines is the most visible alternative.”
He also noted that North Korea may use the development as further justification for keeping its own nuclear arsenal, making future negotiations even more complicated.
Still, researchers like Jo Bee-yun from the Sejong Institute say the deal transforms South Korea into a more influential regional actor. Nuclear submarines, she explained, offer speed and extended range, allowing South Korea to cooperate more closely with allies.
Why the US supports the deal
For Washington, the agreement enhances pressure on both North Korea and China. According to analysts, Trump’s strategy is also pushing Seoul to shoulder more defence responsibilities.
“South Korea will greatly expand its defence budget,” Dr Yang said. “They will essentially serve as a proxy in helping counter China and North Korea.”
China, which has increased maritime activity near Korean waters, is expected to be displeased. Chinese Ambassador Dai Bing urged Seoul to act “prudently” and emphasized that the regional environment remains “complex and sensitive.”
What happens next?
Although Trump stated the submarines would be built in Philadelphia, South Korean officials say the vessels must be constructed domestically to ensure faster delivery. Prime Minister Kim Min-seok has publicly noted that the US-based shipyard lacks the capacity to handle such an advanced project.
Hanwha, the company in question, has not issued a statement.
With political approval secured, the next phase involves updating the countries’ nuclear cooperation agreement so the US can legally supply fuel and define how it may be used for military purposes.
