South Korea’s ambition of deploying nuclear-powered submarines appeared to take a step closer to reality this week, after US President Donald Trump’s declaration that Seoul would build such a vessel in a Korean-owned shipyard in Philadelphia.
But Trump’s announcement on Thursday, a day after he was feted by his South Korean counterpart Lee Jae Myung, raised a host of questions about the implications of such a deal for both regional security and global nuclear proliferation.
Trump declared on his Truth Social platform that South Korea would “be building its Nuclear Powered Submarine in the Philadelphia Shipyards, right here in the good ol’ U.S.A.”.
“Our Military Alliance is stronger than ever before and, based on that, I have given them approval to build a Nuclear Powered Submarine, rather than the old fashioned, and far less nimble, diesel powered Submarines that they have now,” Trump wrote on his social media platform.
His declaration appeared to be a response to a direct request for access to the highly enriched nuclear fuel needed by such submarines that was made by Lee on Wednesday, after he had presented the US president with a golden crown and South Korea’s highest order of merit.
But significant hurdles remain, with Lee’s national security adviser Wi Sung Lac acknowledging this week that the two countries’ existing nuclear agreement excludes military purposes, meaning that “we must make adjustments to complete the process”.
Nuclear-powered submarines would help Seoul track North Korean or Chinese counterparts, whereby “the US military’s burden could be significantly reduced”, Lee told Trump, who was in the south-eastern Korean city of Gyeongju for a regional summit.
Access to enriched uranium fuel has long been the biggest barrier to South Korean development of nuclear submarines, which can move quietly underwater for far longer periods and over much greater distances than conventional ones.
Under an agreement with the US, South Korea is not allowed to reprocess or enrich nuclear fuel without Washington’s consent. On Wednesday, Lee stressed in public remarks to Trump that the submarines his country is seeking would be nuclear-powered but not armed with nuclear weapons.
South Korea has been interested in building its own nuclear-powered submarines since the 1990s, with its enthusiasm growing in recent years amid the unrelenting progress of North Korea’s nuclear weapons programme and Seoul’s deteriorating ties with Beijing.
North Korean state media’s release in March of images of leader Kim Jong Un inspecting the hull of his country’s own nuclear-powered submarine triggered concern that Seoul’s diesel-powered boats might be outmatched.
Some experts have questioned whether South Korea, which last week launched the first of its latest generation of 3,600-ton diesel-electric attack submarines, needs nuclear-powered alternatives.
“Studies have shown that there are many more effective and cheaper ways to conduct anti-submarine warfare in the shallow close seas around Korea,” said Henry Sokolski, executive director of the Nonproliferation Policy Education Center. “All of them are non-nuclear.”
But Peter Ward, a research fellow at the Sejong Institute think-tank in Seoul, said the possibility of North Korea’s access to Russian nuclear propulsion technology in exchange for its support of Moscow’s invasion of Ukraine had created a new threat that Washington had “limited capabilities to deal with”.
“President Trump wants US allies to do more for themselves,” said Ward, while Lee wants Seoul to be more “self-sufficient, able to counter threats but also able to make decisions on its own”.
Despite Lee’s insistence the submarines would not carry nuclear weapons, non-proliferation advocates are concerned about growing support in the country for developing such arms amid mounting fears about North Korea and doubts about the reliability of the US as an ally.
Daryl Kimball, executive director of the Arms Control Association in Washington, said it was unclear what understanding Trump and Lee had reached, but use of enriched uranium for submarine propulsion would require “very complex” International Atomic Energy Agency safeguards.
“If the US seeks to prevent the proliferation of nuclear weapons worldwide, the Trump administration should resist such overtures from allies as strongly as it works to deny adversary access to these dual-use technologies,” Kimball said.
A possible model for South Korea is the trilateral Aukus programme under which the US and UK are helping Australia obtain a fleet of nuclear-powered submarines. The nuclear fuel, which will be supplied by the US, will be delivered to Australia in sealed units that will not require refuelling during their lifetime.
“The Aukus model involves the transfer of complete, welded nuclear reactors and no Australian handling of the enriched uranium fuel to reduce any proliferation risks,” said Peter Lee, a research fellow at the Asan Institute for Policy Studies think-tank in Seoul.
“In many respects, this proposal would more closely bind South Korea to the United States and therefore prevent any independent nuclear breakout option,” he said.
There are also questions about the ability of the Philadelphia shipyard that was acquired by South Korean conglomerate Hanwha last year to produce advanced submarines.
“US shipyards struggle to build and maintain the country’s existing submarine fleet, and the country is increasingly overstretched in its growing competition with China,” the Sejong Institute’s Ward said.
“The Philly Shipyard has only built commercial and naval surface ships, so transforming it into a submarine shipyard, with a new workforce, would be a significant undertaking,” said Lee. “If this bid does not work out in practice, or if it fails to receive bipartisan US support, it could severely undermine South Korea’s ambitions in the long run.”
