South Korea and the U.S. have agreed to jointly develop nuclear-powered submarines as a “strategic priority” to bolster defense capabilities in the region, according to a statement from Seoul’s Ministry of National Defense released Monday. The move marks the first formal acknowledgment by both governments that domestically built nuclear subs—long discussed in private—will become a cornerstone of their military alliance, with construction expected to begin within the next five years.
The announcement comes as North Korea’s advancing ballistic missile program and China’s expanding naval presence in the Yellow Sea have intensified pressure on Seoul to modernize its submarine fleet. A senior U.S. defense official, speaking on condition of anonymity, confirmed that Washington had approved preliminary funding for the project in its latest defense budget, though exact figures remain classified. “This is not just about submarines—it’s about signaling to our allies and adversaries that the U.S.-ROK alliance is entering a new phase of deterrence,” the official said.
Why nuclear submarines? The technical and strategic stakes
South Korea’s current fleet of diesel-electric submarines, including the Dosan Ahn Changho-class vessels, lacks the endurance and stealth of nuclear-powered counterparts. A 2023 report by the ROK Navy’s Research Institute estimated that conventional subs must surface every 48–72 hours for air, requiring silent running periods that limit operational flexibility. Nuclear propulsion, by contrast, enables continuous patrols of up to 90 days without refueling, a capability critical for monitoring North Korea’s coastal missile launch sites.
China’s rapid expansion of its submarine fleet—now numbering over 100 vessels, according to the U.S. Department of Defense’s 2024 China Military Power Report—has accelerated Seoul’s push for nuclear subs. The U.S. has historically restricted nuclear propulsion technology transfers under the Atomic Energy Act, but exceptions have been made for close allies, including the UK’s Astute-class submarines. A South Korean defense analyst, Dr. Park Jong-hoon of the Korea Defense and Security Forum, noted that the agreement includes a “technology-sharing framework” allowing U.S. engineers to assist in reactor design, though final approvals will require congressional review.
How will this affect the U.S.-South Korea alliance?
The nuclear submarine program is the most significant defense collaboration between the two nations since the 2016 agreement to deploy the THAAD missile defense system in South Korea. However, the project faces political hurdles. In the U.S., lawmakers from both parties have raised concerns about proliferation risks, particularly given South Korea’s status as a non-nuclear weapons state under the Nuclear Non-Proliferation Treaty. A spokesperson for the U.S. State Department clarified that the submarines will be “exclusively for defense purposes” and that no nuclear warheads will be loaded aboard.
South Korea’s domestic politics also complicate the timeline. Opposition parties, including the progressive Justice Party, have criticized the move as unnecessary given the country’s existing defense budget constraints. A survey by the Korea Institute for National Unification last month found that 58% of South Koreans support the submarine program, but only 32% believe it will reduce tensions with North Korea. The Ministry of National Defense dismissed these concerns, stating that the project aligns with the 2022 Joint Vision Statement signed by Presidents Yoon Suk-yeol and Joe Biden.
What happens next? The construction timeline and challenges
Construction is expected to begin at Hyundai Heavy Industries’ Ulsan shipyard in 2029, with the first vessel delivered by 2034, according to internal ROK Navy projections obtained by JoongAng Ilbo. The U.S. will provide reactor technology under a classified agreement, while South Korea will handle hull fabrication and weapons integration. A U.S. official involved in the negotiations said that “interoperability with U.S. naval systems” is a top priority, ensuring the subs can operate seamlessly alongside American vessels in the region.
North Korea has not yet responded to the announcement, but state media outlet Rodong Sinmun published an editorial Friday warning that “any attempt to strengthen military cooperation with imperialist powers will only invite retaliation.” Analysts at the International Crisis Group cautioned that the submarine program could escalate regional arms races, particularly if China perceives it as a direct threat to its coastal defense perimeter.
The next critical step will be a joint technical review scheduled for March 2025, where U.S. and South Korean engineers will finalize reactor specifications. Any delays in congressional approval or budget allocations could push back the timeline by years.
