Seoul eyes nuclear-powered subs to counter regional undersea threats

South Korea is moving closer to joining the world’s small group of countries operating nuclear-powered submarines after receiving public approval from United States President Donald Trump, a development that could reshape security dynamics in Northeast Asia.

Seoul has long sought nuclear-powered attack submarines, arguing they would significantly enhance its ability to monitor and counter undersea threats from North Korea and China. Such submarines can remain submerged for extended periods, move faster, and operate more quietly than conventional diesel-electric vessels.

“For South Korea, this would be a game-changer countering North Korea’s undersea threat,” said Yu Jihoon, a research fellow at the Korea Institute for Defense Analyses and a former South Korean submarine officer.

Yu added that nuclear-powered submarines “could transform South Korea’s role within the alliance to be a more capable security provider, so the strategic implications for the South Korea-US alliance are even more significant.”

The issue gained public momentum after South Korean President Lee Jae Myung openly asked Washington to lift long-standing restrictions that bar Seoul from reprocessing spent nuclear fuel, a key hurdle in operating nuclear-powered submarines. A day later, Trump said he had approved South Korea’s plan to build nuclear-powered submarines, describing them as more capable than the country’s existing diesel fleet.

Lee earlier said nuclear-powered submarines would allow South Korea to better track vessels operating near North Korea and China, noting that diesel-powered submarines are limited by shorter submergence times. He also argued the move could “significantly reduce the burden on US forces” in waters around the Korean Peninsula.

Despite the apparent political green light, major questions remain. Experts say it could take at least a decade before South Korea fields its first nuclear-powered submarine, even if regulatory and congressional reviews proceed smoothly. Disagreements also persist over where the submarines should be built, with concerns in Seoul that overseas construction could limit technology transfer and domestic industrial benefits.

South Korea’s defense officials insist the country already has much of the technical capability needed, pointing to its advanced Jangbogo-III diesel-electric submarines. Still, naval leaders acknowledge converting existing designs to nuclear propulsion would be a lengthy process.

The plan has also drawn regional concern. North Korea has warned that South Korea’s pursuit of nuclear-powered submarines could fuel an arms race, while China has urged restraint and adherence to nuclear non-proliferation commitments.