As reported by Hankyoreh on July 18, 2025, Cho Hyun, nominee for South Korea’s Minister of Foreign Affairs, stated during a confirmation hearing that he would seek to amend the U.S.–ROK 123 Agreement to allow for the development or acquisition of nuclear-powered submarines. The 123 Agreement, which governs peaceful nuclear cooperation between South Korea and the United States, currently prohibits the enrichment and reprocessing of nuclear fuel for military applications.
Cho explained that, following internal review and coordination with the U.S., South Korea could consider the introduction of nuclear submarines as a means to strengthen deterrence. Cho confirmed that the recent resolution of a bilateral intellectual property dispute has cleared a major obstacle to resumed high-level technological cooperation between the two countries, particularly in the development of high-assay low-enriched uranium for use in small modular reactors. Cho’s career trajectory includes senior diplomatic posts such as deputy permanent representative to the UN (2006–2008), ambassador to Austria and representative to various Vienna-based international organisations (2011–2014), and ambassador to India (2015–2017). After serving as second vice minister and then first vice minister from 2017 to 2019, he was appointed as South Korea’s permanent representative to the United Nations from 2019 to 2022. On June 23, 2025, President Lee Jae‑myung nominated Cho Hyun to serve as South Korea’s minister of foreign affairs, making him one of eleven nominees for Lee’s incoming cabinet.
Cho’s remarks were made in response to lawmaker Kim Gunn, who noted that the United States may be preparing to allow allies to possess nuclear-powered submarines without raising proliferation concerns. Kim cited reports that North Korea is attempting to acquire nuclear-powered submarines from Russia and is believed to be developing its own, suggesting that nuclear submarines represent the only viable option for South Korea to maintain strategic balance. Lawmaker Yu Yong-weon of the People Power Party proposed that South Korea consider making concessions to the U.S. to enable a revision of the nuclear energy agreement. Cho supported this position, expressing the view that Washington could be convinced that any enrichment or reprocessing activities would remain strictly civilian. He added that with the dispute resolved, South Korea could move forward with efforts to develop fuel for small modular reactors and establish a domestic capability to enrich uranium below 20 percent, as permitted by the 2015 revision of the 123 Agreement.
The U.S.–ROK 123 Agreement, revised in 2015, governs peaceful nuclear cooperation between the two countries. It prohibits South Korea from enriching uranium above 20 percent U-235 or reprocessing spent nuclear fuel unless explicitly authorized by both governments. It also bans the use of U.S.-origin nuclear material for military purposes, including naval propulsion. While the agreement permits limited enrichment under supervision, any amendment would require consent from the U.S. executive branch and potentially from Congress under the terms of the U.S. Atomic Energy Act. U.S. officials, including Secretary of Defense Lloyd Austin, have recently stated that helping South Korea develop nuclear-powered submarines would be difficult due to Washington’s existing commitments under the AUKUS pact with Australia and the United Kingdom. South Korea’s past nuclear research activities, including a secret enrichment experiment disclosed in 2004, continue to influence Washington’s skepticism about expanding South Korea’s nuclear capabilities.
Support for nuclear-powered submarines and related technologies has increased among South Korean political and security circles. Recent assessments suggest that North Korea has completed or is nearing completion of its first nuclear-powered ballistic missile submarine. The vessel, observed during Kim Jong Un’s visit to a shipyard, is estimated to be more than 100 meters in length and approximately 12 meters in diameter. Its large dimensions suggest it may be intended to carry Pukguksong-6 missiles, which are comparable in size to the U.S. Trident system. Such a platform would allow North Korea to increase its nuclear delivery capability from sea-based platforms. Analysts speculate that Russia may have assisted Pyongyang in developing the reactor and sonar technology, although the design is expected to be rudimentary. Nevertheless, North Korea’s progress has accelerated debates in South Korea regarding its own strategic requirements, including discussions around nuclear propulsion as a necessary component of future deterrence capabilities.
South Korea previously initiated a secret nuclear submarine project known as the 362 Project in June 2003 under President Roh Moo-hyun. The plan aimed to build three nuclear-powered attack submarines based on a 4,000-ton French Barracuda-class design, using a Russian-style BANDI-60 reactor fueled with uranium enriched between 21 and 45 percent. The project was supported by the Navy, Korea Atomic Energy Research Institute, and Defense Acquisition Program Administration. By 2004, basic reactor design was reportedly complete. However, the plan was cancelled after news of the project was leaked and the IAEA launched a review of South Korea’s prior nuclear research. Additional factors included resistance from factions within the defense establishment, particularly those who prioritized Aegis destroyers, and concerns about energy and budget constraints. Despite its cancellation, some experts believe the 362 Project demonstrated South Korea’s capacity to build a naval reactor and integrate it into a submarine platform, and could be revived if the necessary political and diplomatic conditions are met.
Although South Korea currently operates diesel-electric KSS-III class submarines with SLBM-launching capability, including the Hyunmoo-4-4, these platforms lack the endurance, speed, and stealth of nuclear-powered equivalents. Batch II of the KSS-III program is in production, with units expected to be delivered through 2031. Think tanks such as the Sejong Institute and the Asan Institute contend that South Korea must adopt a nuclear submarine program as a national-level project and propose exploring trilateral or multilateral cooperation frameworks involving the U.S., Japan, France, or India. Admiral Samuel Paparo, head of the U.S. Indo-Pacific Command, stated in July 2024 that South Korea could pursue nuclear submarines if operational analysis and bilateral discussions warranted it, although he noted that such a step is not presently considered necessary. Other U.S. officials, including Defense Secretary Lloyd Austin, have cautioned that it would be difficult for Washington to support another nuclear submarine project in the near future, citing existing commitments under the AUKUS framework with Australia and the United Kingdom. South Korean nuclear policy expert Lami Kim notes that while South Korean elites generally oppose outright nuclear armament, many favor the pursuit of nuclear latency as a strategic hedge in case of alliance degradation or worsening regional security conditions.
Domestic political support for nuclear-powered submarines has increased alongside advocacy for nuclear latency. Han Dong-hoon, leader of the ruling party, stated on June 25, 2024, that South Korea should develop the potential to build nuclear weapons if necessary, including acquiring enrichment and reprocessing technologies. He described nuclear latency as a realistic response to unpredictable international conditions and limitations of relying solely on alliances. Former ambassador Lee Baek-soon argued that South Korea should act immediately to secure nuclear latency. Hwang Woo-yea, chairman of the ruling party’s Emergency Response Committee, described it as an urgent task. At the Mugunghwa Forum’s inaugural meeting, held on July 9, 2024, multiple speakers explicitly expressed their intent to develop nuclear latency as a way to enable future armament. Some participants referenced the nationalistic novel “The Mugunghwa Flower Has Bloomed,” which depicts a fictional South Korean nuclear weapons program, as symbolic inspiration. Public discussions of modifying South Korea’s Nuclear Promotion Act to reaffirm peaceful use while preserving military options further highlight the dual nature of these political messages.
Public opinion in South Korea has consistently shown high levels of support for nuclear armament or hedging. Recent polls from 2023 to 2025 indicate that more than 70 percent of respondents support developing nuclear weapons or nuclear-powered submarines. However, elite opinion differs. According to an April 2024 poll cited by Victor Cha, only 34 percent of South Korean elites favored nuclear weapons, while 66 percent opposed them. Despite this, elites show interest in nuclear latency, defined as the ability to quickly build weapons without acquiring them, especially to reduce dependence on the U.S. security guarantee and to shorten the time required to develop nuclear weapons in a crisis. Although most do not advocate outright nuclear armament, they endorse acquiring the capability to produce fissile material. This divergence between public enthusiasm and elite caution is reflected in ongoing efforts to secure legal and technical conditions for future flexibility without explicitly violating international commitments.
Developing and operating nuclear-powered submarines requires meeting five interrelated categories of capability. First, a country must possess a compact, shock-resistant naval reactor fueled by highly enriched uranium, typically enriched between 20 and 90 percent, capable of producing high, sustained power levels under confined underwater conditions. Second, it must have an integrated industrial base, including nuclear-certified shipyards, reactor-component manufacturers, and research facilities. Third, the country must operate a national nuclear safety and regulatory framework that includes at-sea operation protocols, radiation containment, and waste management. Fourth, it must develop and train a naval personnel pipeline capable of operating and maintaining the submarine and reactor systems. Fifth, legal and diplomatic authorization is required to enrich or import high-assay uranium for propulsion and to remove fuel from IAEA safeguards if needed. South Korea already has a large civilian nuclear industry, established shipbuilding capabilities, nuclear engineering institutions, and a submarine force trained in SLBM operations. However, it lacks legal permission under the current 123 Agreement to enrich uranium for naval use or to reprocess fuel, making international approval the primary barrier to launching a nuclear submarine program despite substantial domestic capacity.
© 2025, GDC. © GDC and www.globaldefensecorp.com. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to www.globaldefensecorp.com with appropriate and specific direction to the original content.
