North Korea’s nuclear submarine gambit marks a dangerous inflection point in the rise of an authoritarian nexus that challenges established deterrence dynamics.
This month, multiple media outlets reported North Korea’s unveiling of what it says is the completed hull of its first nuclear-powered submarine, marking a significant step in leader Kim Jong Un’s drive to build a survivable, sea-based nuclear deterrent amid rising tensions with the US and its allies.
State media released images showing Kim inspecting the welded hull of what was described as an 8,700-ton “nuclear-powered strategic guided missile submarine” at an indoor construction facility, indicating the vessel has not yet been launched.
North Korea’s leader Kim Jong Un, inspecting what North Korea claims to be the country’s 8,700-ton nuclear-powered submarine, called Seoul’s nuclear-powered submarine development plan ‘an offensive act.’ Photo: KCNA / via Yonhap
Completion of the hull suggests a reactor may already be installed, although North Korea has not disclosed when the submarine will be operational. It is questionable how quickly the country can master reactor safety, quieting technology and long-term sustainment.
Kim first designated a nuclear submarine as a top weapons priority at a ruling Workers’ Party Congress in 2021, framing it as essential to counter what North Korea calls growing “hostile” threats from the US, South Korea and Japan.
This development follows North Korea’s September 2023 reveal of a “tactical nuclear attack submarine” – the Hero Kim Kun Ok. Joseph S. Bermudez Jr. and other writers note in a Beyond Parallel report that the Kim Kun Ok is a conventionally powered, refurbished Soviet Romeo-class submarine modified to carry submarine-launched ballistic missiles (SLBMs).
As to what may be North Korea’s next move, Bermudez and others say that the country could modify its 17 to 20 Romeo-class submarines into a similar configuration, further modify the Hero Kim Kun Ok, or design a new class of ballistic missile submarines.
In view of those options, North Korea may be implementing a dual-track approach to its undersea nuclear arsenal, says Hong Min in a September 2023 article for the Korean Institute of National Unification. According to Hong, the first track is to build conventionally-powered nuclear-armed submarines such as the Hero Kim Kun Ok, while the second track is to build a nuclear-powered submarine.
As for the rationale for a follow-on design to the Hero Kim Kun Ok, Sukjoon Yoon mentions in an October 2023 report for the S. Rajaratnam School of International Studies (RSIS) that while the submarine has regionally significant range, it has significant technical flaws owing to its ad-hoc design, flaws that incllude stability issues and noisiness leading to easy detection.
However, Russia could have been instrumental in helping North Korea get its nuclear submarine program up to speed, with the two authoritarian allies bound together by pragmatic factors and shared hostility to the US-led international order. North Korea has supplied artillery, ballistic missiles and manpower for Russia’s war effort in Ukraine, while Russia has supplied North Korea with energy, currency, food aid and advanced military technology.
In line with transfers of advanced military technology, the Korea JoongAng Daily reported in September 2025 that unnamed South Korean government sources said Russia may have transferred two or three nuclear submarine modules to North Korea during the first half of this year.
The report notes that the modules, taken from decommissioned Russian nuclear submarines, include the reactor, turbine and propulsion unit – the core components of a nuclear propulsion system.
Furthermore, in a South China Morning Post (SCMP) article from the same month, South Korea’s National Security Adviser Wi Sung-lac mentioned that the government could not confirm the existence of such intelligence. However, SCMP notes that while the transfer is highly provocative, it would not be unrealistic given the growing ties between Russia and North Korea. Furthermore, China’s studied silence on North Korea’s nuclear submarine ambitions reinforces its position as a key player in Asia’s shifting deterrence dynamics.
But should a North Korean nuclear-powered submarine ever materialize, it would have profound regional and strategic consequences.
Possibly mirroring Russia’s nuclear propulsion quid pro quo with North Korea, Politico reported in October 2025 that the US Trump administration announced that it would share nuclear propulsion technology with South Korea after calls to the latter to invest $350 billion in the US economy.
However, Politico reports that South Korea’s new nuclear submarines would be built at Hanwha Philly Shipyard, a commercial facility currently not equipped to build nuclear submarines. It also notes that Huntington Ingalls Industries (HII) – the company responsible for building US nuclear submarines – faces two- to three-year delays in building Virginia-class submarines and 18- to 24-month delays for the Columbia-class submarines.
But matching North Korea’s nuclear submarine ambitions by responding in kind may not be the best solution. South Korea may have to grapple with the immense costs of a nuclear submarine program. In Australia, the AUKUS nuclear attack submarines (SSN-AUKUS) may cost up to USD 245 billion over the next three decades, raising the question of whether it would be wise to spend similar resources on just one capability over an extended timespan, or to acquire and improve more conventional capabilities.
Such capabilities may include improved conventional submarines, anti-submarine warfare (ASW) capabilities, or long-range precision strike capabilities intended to threaten North Korea’s leadership.
South Korea must also address the fact that nuclear propulsion sharing with the US requires a long-term political commitment and may also hinder Seoul’s strategic autonomy, all the more important given the unpredictable Trump Administration’s transactional view of alliances.
While nuclear propulsion per se doesn’t automatically mean nuclear weapons, the highly enriched uranium (HEU) used in US nuclear submarine reactors could pose a proliferation risk – possibly bringing South Korea closer to acquiring nuclear weapons.
Sharon Squassoni argues in an article this month for the Bulletin of Atomic Scientists that US support for South Korean nuclear propulsion could indirectly enable nuclear weapons development by legitimizing uranium enrichment and spent fuel reprocessing, both key pathways to fissile material.
Squassoni says that allowing South Korea to pursue indigenous nuclear-powered submarines increases pressure to master enrichment for naval fuel and reprocessing for waste management, eroding longstanding US nonproliferation restraints.
She notes that these capabilities, while nominally civilian, create a latent or “virtual” nuclear weapons option by shortening breakout timelines and complicating safeguards, especially given loopholes for naval fuel in International Atomic Energy Agency (IAEA) rules. In line with that, Squassoni points out that US approval risks conferring de facto latent nuclear-weapon-state status on South Korea.
While the idea of South Korea arming itself with nuclear weapons is extreme, it may gain traction amid doubts about US extended deterrence guarantees. A US military debacle in the Taiwan Strait or the South China Sea – whether a defeat by China or a US refusal to assist Taiwan or intervene in a limited South China Sea skirmish involving the Philippines – could expose US weakness and decline, irreparably damaging the credibility of its alliances.
While North Korea’s nuclear submarine ambition may not yet have gone critical, it is already powering a dangerous chain reaction across Asia.
