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Seoul and Washington deliver conflicting messages about nuclear-powered submarines

Published: 03 Nov. 2025, 17:28

President Lee Jae Myung, right, and U.S. President Donald Trump walk to the Korea-U.S. summit venue at the Gyeongju National Museum in North Gyeongsang on Oct. 29. [PRESIDENTIAL OFFICE]

A bold bid by Korea to build its own nuclear-powered submarines, or SSNs, has hit turbulence, as conflicting messages from Washington and Seoul expose deep cracks over who will actually construct the vessels — and where.

During a summit last Wednesday, President Lee Jae Myung requested U.S. approval for the supply of nuclear fuel, to which U.S. President Donald Trump responded the next day by saying he had approved Korea’s construction of SSNs — albeit with the caveat that they be built in the United States.

“South Korea will be building its Nuclear Powered Submarine in the Philadelphia Shipyards, right here in the good ol’ U.S.A.,” Trump wrote on Truth Social, his social media platform, on Thursday.

However, confusion soon followed. Wi Sung-lac, the national security adviser, clarified on Saturday that Seoul had specifically sought U.S. cooperation regarding fuel.

“There has been some confusion due to various remarks, but our request was primarily for assistance with fuel,” he said. “That’s what we received approval for because the fuel is for military use.”

The clarification highlights a fundamental issue: The existing Korea-U.S. nuclear cooperation agreement restricts the use of nuclear material to peaceful purposes. To use highly enriched uranium for military propulsion systems such as SSNs, a separate bilateral agreement is required.

Seoul is now considering such a separate pact — distinct from broader efforts to revise the main agreement to expand Korea’s rights to enrich and reprocess nuclear material for industrial purposes.

Industry experts say that Korea, as a global shipbuilding powerhouse, already has the technological capacity to develop and build nuclear submarines, provided it can secure access to the necessary fuel. However, even in the best-case scenario, the navy estimates that construction would take at least a decade.

U.S. President Donald Trump, left, shakes hands with President Lee Jae Myung as Trump receives a gold crown and the Grand Order of Mugunghwa, not seen, as gifts during a high honor ceremony at the Gyeongju National Museum in North Gyeongsang on Oct. 29. [AP/YONHAP]

One alternative reportedly under discussion is for the United States to supply sealed nuclear fuel modules while effectively denying Korea the ability to produce or manage the fuel itself. But this would leave Korea heavily dependent on Washington for submarine operation and maintenance, undermining its autonomy.

“There’s growing concern that without independent fuel production capabilities, Korea’s nuclear-powered submarines would be vulnerable to U.S. policy shifts,” said Lee Byong-chul, a professor at the Institute for Far Eastern Studies at Kyungnam University. “Trump’s comment that the submarines should be built in the United States was effectively a non sequitur — unrelated to President Lee’s actual request.”

He warned that if Korea is only allowed to import sealed fuel modules, a halt in U.S. supply could render the country’s multibillion-dollar submarine fleet inoperable.

“This isn’t the path to nuclear armament, as some mistakenly believe. It’s a logistics and sovereignty issue,” Lee added.
Trump’s remarks have also drawn scrutiny for their lack of specificity. Korea requested approval for nuclear fuel supply, but Trump abruptly posted on social media that he would approve submarine construction — as long as it took place in the United States — leaving the context of his response unclear.

For Korea to construct submarines in the United States, the Philly Shipyard would first need to be designated as a defense contractor under U.S. law — potentially limiting the autonomy of its owner, the Korean shipbuilder Hanwha Ocean.

Chief of Naval Operations Adm. Kang Dong-gil, center, answers questions from lawmakers during a parliamentary audit of the National Defense Committee at the National Assembly in Yeouido, western Seoul, on Oct. 30. [YONHAP]

Further complicating matters, the Philly Shipyard currently lacks the infrastructure to build nuclear submarines.

“Submarine construction requires heavily reinforced concrete bases and enclosed facilities, which the yard does not have,” said Chief of Naval Operations Adm. Kang Dong-gil during a parliamentary audit on Thursday.

Rep. Yu Yong-weon, a former military correspondent and member of the People Power Party, added, “The yard only has two docks and a large crane. Korea expects to build the hulls and reactors domestically and source only the fuel from the United States.”

The controversy has led to speculation that Trump’s approval may have more to do with boosting U.S. shipbuilding than enabling Korea’s strategic capabilities.

“Trump’s statement essentially undercut Korea’s vision for self-reliant nuclear submarines,” said Park Won-gon, a professor of North Korean studies at Ewha Womans University. “The Philly Shipyard lacks the necessary infrastructure, and even if it didn’t, building there would require congressional approval and defense contractor certification, making it highly impractical.”

Park urged the Korean government to negotiate clearly and strategically.

“Korea should treat its potential $150 billion investment in the U.S. Make American Shipbuilding Great Again initiative as leverage to secure domestic construction rights and enriched uranium use,” he said.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
BY CHUNG YEONG-GYO,PARK HYUN-JU [[email protected]]