US will share tech to let South Korea build a nuclear-powered submarine, Trump says

This handout photo taken on July 24, 2023 and provided by the South Korean Defense Ministry shows the USS Annapolis, a US nuclear-powered submarine, arriving as South Korean soldiers wave flags at a naval base in South Korea's southern island of Jeju. (AFP)

President Donald Trump shakes hands with South Korean President Lee Jae Myung during a dinner event in Gyeongju, South Korea, on Oct. 29, 2025. (AP Photo)

• President Lee Jae Myung clarified to Trump that his country was not seeking nuclear weapons but submarines that run on nuclear fuel

GYEONGJU, South Korea: The United States will share closely held technology to allow South Korea to build a nuclear-powered submarine, President Donald Trump said on social media Thursday after meeting with the country’s president.
President Lee Jae Myung stressed to Trump in their Wednesday meeting that the goal was to modernize the alliance with the US, noting plans to increase military spending to reduce the financial burden on America.
The South Korean leader said there might have been a misunderstanding when they last spoke in August about nuclear-powered submarines, saying that his government was looking for nuclear fuel rather than weapons.
Lee said that South Korea’s current diesel-powered submarines have limits in tracking other countries’ submarine activities. If South Korea was equipped with nuclear-powered submarines, he said, it could help US activities in the region.
Diesel-powered submarines have to surface regularly to recharge their batteries. But nuclear-powered submarines have superior endurance and can stay submerged for a significantly longer period.
Trump said in a separate post that the country would build its nuclear-powered submarine in the Philly Shipyard, which was bought last year by South Korea’s Hanwha Group.
It was unclear what the size or cost of the sub project would be, but South Korea had said as part of talks with Trump that it had committed $150 billion to invest in America’s shipbuilding capacity.
US nuclear submarine technology is widely regarded as some of the most sensitive and highly guarded technology the military possesses. The US has been incredibly protective of that knowledge, and even a recently announced deal with close allies the United Kingdom and Australia to help the latter acquire nuclear submarine technology doesn’t feature the US directly transferring its knowledge.
Trump’s post on social media comes ahead of his meeting with Chinese President Xi Jinping, whose country possesses nuclear submarines, and after North Korea in March unveiled for the first time a nuclear-powered submarine under construction. It is a weapons system that can pose a major security threat to South Korea and the US
As Trump visited South Korea, North Korea said Wednesday that it conducted successful cruise missile tests, the latest display of its growing military capabilities.
Pentagon officials didn’t immediately respond to questions about Trump’s announcement on sharing the nuclear sub technology with South Korea.