U.S. President Donald Trump has announced that Washington will permit South Korea to construct nuclear-powered submarines in the United States, marking a major shift in defense cooperation between the two allies.

According to Trump, the submarines will be built at Philly Shipyard in Philadelphia — a facility recently acquired by South Korea’s Hanwha Group. The decision, unveiled Thursday on Trump’s Truth Social account, means Seoul will gain access to advanced U.S. nuclear propulsion technology previously kept under tight control.

“I’ve approved South Korea to build a nuclear-powered submarine instead of the slower, diesel-powered ones they currently operate,” Trump wrote.

The agreement underscores Washington’s deepening military partnership with Seoul and could have broader implications for regional security, particularly for Japan, which continues to debate expanding its own defense capabilities.

South Korea has long expressed interest in nuclear-powered submarines to strengthen its deterrence against North Korea and enhance its ability to operate for longer periods underwater. Building them in the United States could also further cement South Korea’s growing investment footprint in the American defense industry.

The move is expected to draw close attention from neighboring countries, as it signals a new phase of military collaboration under Trump’s administration and reflects Seoul’s ambition to expand its naval power beyond conventional limits.