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A multibillion-dollar windfall for shipbuilders: Trump's approval fuels Korea’s nuclear submarine drive

Published: 30 Oct. 2025, 19:28

CHO YONG-JUN
[email protected]

The USS Vermont (SSN-792), a U.S. Virginia-class nuclear-powered attack submarine, arrives at the HMAS Stirling naval base in Perth, Australia on Oct. 29. [AFP/YONHAP]

[EXPLAINER]

U.S. President Donald Trump's green light for Korea to develop its own nuclear-powered submarine has stirred both industrial and security reverberations, reviving a long-deferred ambition first attempted in 2003.

Other than the fact than that Korea will acquire four nuclear submarines, each weighing over 5,000 tons, by the mid-2030s or later, according to Chief of Naval Operations Kang Dong-gil on Thursday, not much has been disclosed to how Korea will be constructing and deploying it.

And while the verbal approval itself is a significant step forward for Korea, lots of future discussions, amendments and time will be required before Korea actually constructs and deploys a nuclear submarine.

What approval did Trump give to Korea?

Trump said he gave Korea “approval” to build a nuclear submarine, commonly classified by the U.S. Navy as a general-purpose nuclear-propelled submarine, or SSN.

“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 Truth Social on Thursday.

Trump’s approval follows Lee’s official request during the summit held on Wednesday, during which he asked Trump to decide whether the United States would “supply fuel for a nuclear submarine” to Korea.

Lee claimed that allowing the Korean navy to have its own nuclear submarine will help it better defend the seas, “relieving the burden from U.S. forces.”

How big of a deal is it?

It’s a pretty big deal — in theory.

The Korean Navy currently operates only diesel-electric-powered conventional submarines.

The main difference between an SSN and a conventional submarine lies in how long it can remain submerged and operate without periodically resurfacing or returning to port. While diesel- or battery-powered submarines can stay submerged for a few days, a nuclear-powered submarine can remain under the sea for months, offering a wider operational radius and reducing vulnerability.

Why hasn't Korea built a nuclear submarine before?

Korea was never systematically banned from operating a nuclear submarine, but the so-called 123 agreement between Korea and the United States safeguards the operation. Also known as the U.S.-Korea Agreement for Peaceful Nuclear Cooperation, the 123 agreement regulates the use of U.S.-sourced nuclear materials for peaceful purposes only.

The agreement also requires Korea to use enriched uranium with U.S. approval, and it bans the country from reprocessing spent nuclear fuels. So Korea either has to directly receive enriched uranium from the United States or receive approval to enrich the element within the country, both of which require significant amendments to the agreement.

Korea had previously tried to develop its own 4,000-ton-class nuclear submarine in the early 2000s before the project was scrapped for political and logistical reasons. Former President Moon Jae-in had also pledged to build a nuclear submarine, but he was ultimately unable to do so.

Does this mean that Korea can now own submarines firing nuclear missiles (SSBNs)?

No. Lee specifically mentioned that Korea “is not constructing a submarine with nuclear weapons on board,” or SSBNs, but multiple submarines that are “nuclear-powered.”

The president also asked the United States to supply Korea with the nuclear fuel required for the SSN: enriched uranium.

Hanwha Philly Shipyard in Philadelphia [JOONGANG ILBO]

Can the Hanwha Philly shipyard build a nuclear submarine at the moment?

No, at least for now, since the small shipyard was only designed to build commercial ships and container vessels.

Trump, in a following post on Truth Social, said that Korea “will be building its Nuclear Powered Submarine in the Philadelphia Shipyards, right here in the good ol’ U.S.A.,” which likely refers to the Hanwha Philly Shipyard that the Korean shipbuilding firm Hanwha Ocean acquired in 2024.

The shipyard now acts as a key to the Make American Shipbuilding Great Again (MASGA) project, which the Korean government proposed to the United States, aiming to revitalize the U.S. shipbuilding industry.

But Hanwha Ocean, which has historically constructed diesel-powered submarines, doesn’t have any experience in building nuclear submarines, though the company has previously worked on the development of technologies required for the construction of a nuclear submarine, according to the JoongAng Ilbo.

The Philly Shipyard, too, is a not-so-large shipyard featuring two docks. The shipyard has only built container ships and cargo ships, not submarines or any military ships.

Hanwha Ocean also confirmed to the JoongAng Ilbo that its shipyard currently has no means of constructing submarines and hopes for “nationwide aid” to upgrade the facilities.

What hurdles are left before Korea can construct and deploy its nuclear submarine?

Multiple future talks, amendments and approvals remain before Korea can own its first nuclear submarine.

Mainly, Korea would have to either amend its 123 agreement with the United States or sign a separate document that allows Korea to use nuclear technology for military use without violating the agreement.

Korea would also have to talk with the International Atomic Energy Agency to prove that Korea's use of nuclear energy in submarines will not result in Korea developing its own nuclear weapons.

The nuclear propulsion technology — which will power the nuclear submarines — is also an issue. Only a select number of nations, including the United States, have the propulsion technology, and Korea would either have to develop its own power or have the United States transfer the technology, which it has only done for the United Kingdom so far.

BY CHO YONG-JUN [[email protected]]