The Indo-Pacific region is one of the areas where hegemonic competition is most intense in today’s international system. This environment is further complicated by the military applications of nuclear technologies. On October 30, 2025, following a meeting with US President Donald Trump, South Korean President Lee Jae-myung reached an important agreement on nuclear-powered attack submarines (SSNs). According to this agreement, South Korea will receive technical assistance from the US in the field of SSNs, and nuclear fuel transfers will take place. [i] This represents a strategic turning point in the competition. Announced at the Asia-Pacific Economic Cooperation (APEC) Summit, this agreement will transform South Korea’s defense capabilities and directly impact the integrity of the AUKUS alliance, Japan’s nuclear concerns, and North Korea’s perception of threat.[ii]
Strategically, the agreement reflects the pragmatic diplomacy of the United States toward its allies. The controlled transfer of nuclear technology strengthens alliance ties through economic investments and commitments to regional stability in return.
South Korea’s SSN strategy dates back to the early 2000s. It stems particularly from the search for asymmetric deterrence against North Korea’s ballistic missile submarines (SLBMs) and conventional submarine fleet. South Korea views these platforms as a strategic lever for power projection in broader Indo-Pacific areas such as the South China Sea and the Taiwan Strait, beyond the security of the Korean Peninsula. However, this goal has long been hindered by domestic political dynamics and the current state of the international regime. The secondary position of the navy within the South Korean Armed Forces, conservative governments (Yoon Suk-yeol era, 2022-2024) failure to prioritize SSN projects and the 1974 bilateral nuclear cooperation agreement with the US limiting uranium enrichment to below 20% have hampered progress. The obligations of the Nuclear Non-Proliferation Treaty (NPT) also reinforce these restrictions.
Interest in the SSN as a strategic deviation is associated with left-leaning administrations (such as Lee Jae-myung). This reflects a lack of trust in the military. Yoon’s brief martial law initiative in December 2024 and the military’s support for the initiative accelerated the Lee administration’s navy-focused strategies. Trump’s second term as president presented an opportunity to break this status quo. At the APEC Summit, Lee persuaded Trump to restructure the agreement rather than abandon the Biden legacy AUKUS. In exchange for SSN approval, Trump secured a commitment from South Korea for $350 billion in US investment, tariff reductions, and the “Make America Great Again in Shipbuilding” initiative. This deal embodies Trump’s “America First” doctrine. In particular, the Trump administration is increasing ally dependency by using nuclear technology as an economic lever.[iii] South Korea’s 30-year effort has finally paid off. In parallel with this development, China and Japan may accelerate their own SSN programs in the region.[iv]
The agreement provides South Korea with high-enriched nuclear fuel from the US and technical support for the design and construction of SSNs. According to Trump’s statement on October 30, 2025, the fuel transfer indirectly relaxes NPT norms, granting Seoul diplomatic legitimacy for the use of military nuclear power. The first phase of construction will take place at Hanwha Ocean’s Philadelphia Shipyard, a choice that reflects Trump’s domestic employment priorities. However, the US submarine industry is already at capacity with an annual production of 1.3 SSNs and the AUKUS workload.[v]
South Korea plans to close this gap by sending its own engineers and equipment to the US. In the long term, the agreement opens the door to domestic production of SSNs at the Ulsan or Geoje shipyards. Seoul’s advantages are clear: 50 years of civil nuclear experience (APR-1400 reactors), over 100,000 STEM graduates annually, major defense industry players such as Hyundai Heavy Industries, and the KSS-III conventional submarine program.[vi]
The estimated cost is $12-18 billion for the first phase and will be financed by a 15% increase in the 2026 defense budget. However, the 20% fuel enrichment limit restricts full autonomy. US Defense Secretary Pete Hegseth’s visit to Seoul on November 3, 2025, reinforced the operational integration of the agreement.[vii] Hegseth and South Korean Defense Minister Ahn Gyu-back visited the Joint Security Area (JSA) ahead of the 57th Security Consultative Meeting (SCM), emphasizing the symbolism of the alliance. The SCM agenda includes expanded deterrence, cyber-missile defense, and wartime operational control (OPCON) transfer.[viii]
The most critical strategic implication of the agreement concerns the transfer of SSNs under Pillar 1 of AUKUS. Australian Prime Minister Anthony Albanese denied integration speculation on October 31, 2025. However, Trump’s sharing of nuclear propulsion with an ally outside the Five Eyes is eroding AUKUS’s exclusivity.[ix]
The agreement with Japan is a factor that triggers its nuclear trauma. Tokyo is skeptical of military nuclear power due to its commitment to the NPT. Japan, which remained silent during APEC, privately accuses Trump of undermining norms.
Defense Minister Shinjiro Koizumi’s meeting with Hegseth in Tokyo on October 29, 2025, is an effort to salvage QUAD coordination. In this regard, it may lead Japan to accelerate its own SSN program. Ultimately, the South Korea-US nuclear submarine agreement, announced on October 30, 2025, represents a strategic move that constitutes a permanent fracture point in the security architecture of the Indo-Pacific region. The agreement not only transforms South Korea’s defense capabilities but also reinforces the paradigm of the US using technology transfer as an economic and political lever in its alliance relationships.
Conducted under the Trump administration’s “America First” doctrine, this deal reshapes alliance ties through the controlled sharing of nuclear propulsion technology while creating an asymmetric shift in the regional balance of power. In the short term, Seoul gains deterrence superiority against North Korea’s ballistic missile submarine threat. In the long term, it increases its power projection capacity in critical sea lanes such as the South China Sea and the Taiwan Strait. This situation necessitates the repositioning of the US-centered alliance system against China’s claim to regional hegemony.
[i] “Why South Korea wanted an SSN deal with the US and what it may mean for Australia”, ASPI, https://www.aspistrategist.org.au/why-south-korea-wanted-an-ssn-deal-with-the-us-and-what-it-may-mean-for-australia/, (Date of Access: 03.11.2025).
[ii] Ibid.
[iii]“Trump says South Korea has approval to build nuclear-powered submarine”, Reuters, https://www.reuters.com/world/china/trump-says-south-korea-has-approval-build-nuclear-powered-submarine-2025-10-29, (Date of Access: 03.11.2025).
[iv] “South Korea’s 30-year quest for nuclear submarines pays off”, Breaking Defense, https://breakingdefense.com/2025/10/trump-south-korea-nuclear-submarines-china/, (Date of Access: 03.11.2025).
[v] “Can the U.S. Navy Really Build 3 Submarines Per Year?”, The National Interest, https://nationalinterest.org/blog/buzz/can-us-navy-really-build-3-submarines-year-213743, (Erişim Tarihi: 03.11.2025); “Congressional analysis lays bare AUKUS challenges as Australia looks to arm future submarines with hypersonics”, ABC, https://www.abc.net.au/news/2025-01-17/us-congressional-analysis-blunt-on-aukus-difficulties/104826856, (Date of Access: 03.11.2025).
[vi] “S. Korea and US defense chiefs visit JSA ahead of talks on nuclear subs, OPCON transfer”, Korea Times, https://www.koreatimes.co.kr/southkorea/defense/20251103/s-korea-us-defense-chiefs-visit-jsa-ahead-of-talks-on-nuclear-subs-opcon-transfer, (Date of Access: 03.11.2025).
[vii] Ibid.
[viii]“Hegseth visits South Korea for talks on U.S. troops, tour of DMZ border”, Reuters, https://www.reuters.com/business/aerospace-defense/hegseth-visits-south-korea-talks-us-troops-tour-dmz-border-2025-11-03, (Date of Access: 03.11.2025).
[ix] “The mystery of South Korea’s nuclear-powered submarines”, Lowy Institute, https://www.lowyinstitute.org/the-interpreter/mystery-south-korea-s-nuclear-powered-submarines, (Date of Access: 03.11.2025).
