Trump Approves South Korean Nuclear Submarine Plan Linked to $350 Billion Trade Package

Philadelphia submarine pledge joins trade relief and defense cooperation

President Donald Trump has approved South Korea's pursuit of a nuclear powered submarine and named Philadelphia as its construction site, connecting a major defense initiative to a trade arrangement involving an estimated $350 billion in South Korean investment in the United States. About $150 billion of that package is described as support for American shipbuilding capacity.

The announcement followed a summit with South Korean President Lee Jae Myung in Gyeongju ahead of Asia Pacific Economic Cooperation meetings. The economic package also includes purchases of American oil and gas and a reduction in US tariffs on Korean imports from 25 percent to 15 percent. That is a reduction of 10 percentage points, while the proposed shipbuilding support represents about 43 percent of the investment total.

Lee sought access to fuel for submarine propulsion and said Seoul was not seeking submarines armed with nuclear weapons. A reactor would supply power to move the vessel and operate its equipment. Nuclear weapons would be a separate capability, which South Korea says is outside its goal.

Trump presented the announcement as evidence of stronger security ties. Writing on Truth Social, the US president said:

Our Military Alliance is stronger than ever before.

Trump also linked the project to manufacturing and employment in American shipyards:

Shipbuilding in our Country will soon be making a BIG COMEBACK.

As of October 30, 2025, the announcement provides political approval, while the binding details of the broader package and the submarine's technical arrangements remain incomplete. The reactor's origin, fuel supply, safeguards, construction arrangements and delivery timetable have yet to be settled.

What Washington has approved

Trump's decision opens a path for Seoul to pursue nuclear propulsion and for work to begin on a construction plan in the United States. A successful program would place South Korea among the small group of nations operating submarines powered by reactors.

South Korea's Industry Ministry, however, said its officials had not participated in detailed discussions about building a submarine in Philadelphia. That leaves a gap between the president's proposed location and the industrial planning needed to make it possible.

The Philadelphia facility is a commercial shipyard. It does not currently handle nuclear material or military shipbuilding. In the United States, only two shipyards, one in Connecticut and one in Virginia, currently build nuclear submarines for the US Navy.

Those facilities work under rigorous oversight from Naval Reactors, the joint Navy and Department of Energy program that manages every aspect of naval nuclear propulsion safety. Work involving a naval reactor requires specialized facilities, tightly controlled procedures and workers trained to meet demanding safety and quality standards.

Philadelphia would need extensive upgrades, dedicated facilities and years of workforce training to meet those requirements. Technical, legal and industrial decisions will determine whether construction proceeds there, in South Korea, or through an arrangement sharing work between the two countries.

Why Seoul wants longer underwater endurance

South Korean officials argue that their conventional submarines have shorter underwater endurance, limiting their ability to track North Korean and Chinese submarines for sustained periods in surrounding seas. A nuclear reactor offers a different source of power from the diesel engines and batteries used by conventional boats.

A nuclear powered submarine can stay submerged for months. Food supplies and the crew's ability to remain at sea become greater limits than the need to recharge batteries. It can also maintain higher speeds for longer periods and is harder to detect over time because it can remain underwater.

Diesel electric submarines remain effective ambush platforms in coastal waters. Some designs use air independent propulsion, equipment that extends underwater endurance without the usual need to obtain air for diesel engines. Even with that improvement, conventional boats must come up more often and have less sustained reach in the open ocean than submarines powered by reactors.

South Korea has already invested heavily in advanced conventional submarines, including its KSS III class. Those vessels are large, quiet and equipped for long patrols. Seoul's interest in nuclear propulsion adds a longer range tracking capability to that existing investment.

North Korea is pursuing new undersea capabilities, including efforts to field submarines that can launch ballistic or cruise missiles. China has the world's largest navy and is increasing the sophistication and reach of its submarine force. Seoul sees nuclear powered boats as a way to follow those fleets over longer distances and reduce its reliance on American submarines for persistent underwater surveillance.

Pyongyang's strengthened military and economic ties with Russia add to the tensions surrounding the proposal. Claims of Russian technical assistance to North Korea, including claims that Pyongyang seeks a submarine powered by a reactor, are also encouraging further South Korean requests. Trump said he had been unable to arrange a meeting with North Korean leader Kim Jong Un during this visit.

The reactor and fuel decisions

Naval nuclear propulsion depends on a compact reactor capable of powering a submarine for long periods without refueling. Its design and fuel are central to the project because they affect endurance, maintenance, safety and the rules governing transfers between countries.

The United States and the United Kingdom use uranium fuel with very high enrichment levels in their naval reactors. France uses fuel with lower enrichment. Enrichment increases the proportion of the uranium material that can sustain a nuclear reaction.

Any arrangement involving American nuclear technology or material brings nonproliferation rules and inspections into the process. The allies would need a way to supply fuel and keep it under credible monitoring while protecting sensitive submarine technology.

South Korea's civilian nuclear cooperation with Washington operates under a bilateral accord known as a 123 agreement. It restricts enrichment and reprocessing involving fuel derived from US technology or material unless Washington grants consent. Reprocessing separates materials from used nuclear fuel, including plutonium.

Lee asked for a decision allowing South Korea to receive fuel for submarine propulsion. He also sought support for progress on enrichment or reprocessing in some form, activities that remain restricted under the existing agreement.

Daryl Kimball, executive director of the Arms Control Association, said naval propulsion for an ally requires careful handling. He described the proposal as raising a range of unresolved issues:

raises all sorts of questions

Kimball also said supplying the technology and fuel would require new monitoring arrangements through the International Atomic Energy Agency, or IAEA, which implements the Treaty on the Non Proliferation of Nuclear Weapons, known as the NPT:

would require a very complex new regime of safeguards

The allies will need to choose whether the reactor is supplied as a sealed unit or designed and manufactured with South Korean participation. That choice would help determine how much technology is shared and how the fuel is managed.

How AUKUS changed the discussion

The 2021 agreement between Australia, the United Kingdom and the United States, known as AUKUS, created a route for Australia to acquire nuclear powered submarines using American and British technology. It broke a longstanding pattern of extreme restraint in sharing naval nuclear propulsion expertise beyond the United Kingdom.

South Korea saw that agreement as evidence that a partner could gain access to the capability within a close alliance and under strict safeguards. AUKUS gave Seoul a practical precedent for seeking its own arrangement.

Australia's approach differs from South Korea's requests. Australia is not seeking domestic enrichment or reprocessing, and its submarine plan centers on reactor units supplied under stringent controls. Seoul has asked for broader rights over activities in the nuclear fuel cycle.

Enrichment and reprocessing expertise can shorten the technical route to nuclear weapons if a country later chooses that course. South Korea's request therefore brings scrutiny extending beyond the design of the submarine itself, even though Seoul says its purpose is propulsion.

What Philadelphia would need to build

Trump identified a Philadelphia yard now owned by Hanwha, a major South Korean industrial group. Hanwha Philly Shipyard has built commercial vessels such as container ships and tankers. It is not currently configured for military construction or nuclear propulsion.

Converting the yard would require major capital spending, new certifications, security improvements and an experienced supply chain. A submarine's reactor compartment and supporting equipment demand manufacturing and inspection practices different from those used for ordinary commercial vessels.

The required changes would likely include:

• Secure dry docks with the size and strength needed for submarine modules.
• New buildings for reactor compartment assembly and radiological work, with strict access controls.
• Heavy lift cranes, precise alignment equipment and fixtures for holding components during modular construction.
• A certified supply network for reactor grade piping, valves, pumps and instruments.
• Quality assurance systems meeting Navy and Naval Reactors standards, including testing that checks components without damaging them.
• Training programs for thousands of welders, pipefitters, electricians, machinists and inspectors.
• Arrangements for handling spent materials and meeting federal radiological safety requirements.

A yard starting a new submarine program would also need heavy fabrication halls, clean assembly spaces and testing facilities. Recruiting workers and teaching specialized welding and nuclear quality procedures would take years. Naval Reactors would oversee practices meeting stringent standards for reactor compartments and the rest of the vessel.

Existing submarine delays could affect the project

American submarine builders are already dealing with worker shortages, supplier bottlenecks and quality control backlogs. Those problems affect both attack submarines and the new class of submarines carrying ballistic missiles.

Delivery schedules for Virginia-class attack submarines have slipped by roughly two to three years in many cases. The first Columbia-class submarine has faced delays of about one and a half to two years.

A South Korean project using the same skilled trades and critical components would face those pressures too. Investing in an additional yard would require expanding the workforce and supply network as well as constructing new buildings.

South Korean defense officials say they are developing compact reactors and could build one faster than the decade such work often requires. A reactor would still have to be integrated into a hull, alongside a complete combat system. The program would need qualified crews and testing to establish quiet operation and safety.

The United States developed those processes over generations. A new yard would have to build the experience needed to perform them consistently, making industrial preparation central to the submarine's eventual schedule.

The economic bargain behind the security decision

South Korea's estimated $350 billion investment commitment places the submarine announcement within a broader agreement covering trade, energy and industry. Official statements in both countries describe about $150 billion as support for American shipbuilding capacity.

The package also calls for Seoul to buy more American oil and gas and for US tariffs on Korean imports to fall from 25 percent to 15 percent. For Korean exporters, the lower tariff would reduce the tax imposed when covered goods enter the American market.

The White House and Congress have sought foreign investment to rebuild American shipbuilding capacity after decades of erosion in the commercial sector. Trump has presented South Korean participation as a source of American manufacturing jobs and a demonstration of close alliance coordination.

South Korean officials describe the investment as a way to deepen industrial ties and gain access to critical technology. The arrangement combines security commitments and advanced propulsion access with capital, market access and energy purchases.

Kim Dong yup, a professor of North Korea studies at Kyungnam University, argued that the summit formalized an arrangement linking security guarantees to economic contributions. He warned that the bargain favors Washington's interests and could reduce Seoul's freedom to make policy choices. He described it as:

the commercialisation of the alliance and the commodification of peace.

The commercial terms and the submarine proposal now require detailed agreements that turn those political commitments into workable investment and defense programs.

China's response and the safeguards challenge

China's foreign ministry urged the United States and South Korea to meet their nuclear nonproliferation obligations. Its response reflects concern about the sensitive materials and knowledge involved in naval reactors.

Under the NPT, countries without nuclear weapons can remove nuclear material from safeguards for naval use under strict conditions, although the practice is rare. The IAEA would need a tailored verification arrangement that keeps fuel tracked and secure while protecting classified submarine design information.

South Korea says it wants conventionally armed submarines powered by reactors. Such propulsion is allowed under the NPT when properly safeguarded. The choice of fuel and any additional permission for enrichment or reprocessing would still carry consequences across the region.

Kimball argued that acquiring capabilities to separate plutonium or enrich uranium remains technically and militarily unnecessary for South Korea. His position is that the alliance can meet deterrence needs through other assets, while a propulsion program should preserve longstanding limits on sensitive nuclear technologies.

Analysts in Washington also point to claims of Russian assistance to North Korea as a reason Seoul may expand its requests. Requests extending further into enrichment or reprocessing would make the IAEA's safeguards task more difficult and sharpen debate with Beijing and other regional governments.

From the summit to a construction program

The allies must develop a detailed framework for transferring technology, establish a fuel supply arrangement and agree on monitoring and inspection rights. Naval Reactors would oversee safety and quality for work performed in the United States.

Congress will likely be consulted on parts of the project involving export controls and security cooperation law, as happened with AUKUS. An industrial plan would also need to set out Philadelphia's upgrades, workforce recruitment and design milestones.

The sequence leading to the current proposal is:

• 2021: Australia, the United Kingdom and the United States established AUKUS, creating a route for Australia to acquire nuclear powered submarines.
• The Gyeongju summit ahead of the Asia Pacific Economic Cooperation meetings: Lee sought access to submarine fuel, and Trump announced approval for South Korea's submarine plan with Philadelphia as the proposed construction site.
• October 30, 2025: The proposal was linked to the trade and investment package, while the reactor, safeguards and industrial arrangements still required decisions.

The next markers are a formal decision on the propulsion source, any American consent for fuel activities under the bilateral nuclear agreement, a construction roadmap for Philadelphia and initial design and training milestones. Those decisions will determine whether the project gains early momentum or develops through a gradual expansion across the decade.

At a Glance

• Trump approved South Korea's pursuit of a nuclear powered submarine and named Philadelphia as the construction site.
• The trade package includes an estimated $350 billion in investment, with about $150 billion supporting American shipbuilding.
• The arrangement includes American oil and gas purchases and a tariff reduction from 25 percent to 15 percent.
• Lee requested submarine fuel access and said Seoul is not seeking submarines armed with nuclear weapons.
• Hanwha Philly Shipyard currently builds commercial vessels and would need extensive upgrades for nuclear submarine work.
• Existing American submarine programs face delivery delays, labor shortages and supply constraints.
• Reactor sourcing, nuclear safeguards, fuel permissions and construction planning require further agreement.
• China called for compliance with nonproliferation obligations, while Kimball warned against unnecessary enrichment and reprocessing capabilities.