Russia’s suspected transfer of nuclear submarine reactors to North Korea has jolted East Asia, tying Pyongyang’s submarine ambitions to Moscow’s war in Ukraine while raising new doubts about the US’s deterrent staying power in the Pacific.
This month, multiple outlets citing South Korean intelligence reported that Russia may have covertly transferred two to three decommissioned nuclear submarine modules—including a reactor, turbine and cooling system—to North Korea in the first half of 2025, potentially giving Pyongyang access to propulsion technology it has long lacked.
Officials say the deal followed North Korean Supreme Leader Kim Jong Un’s repeated requests for nuclear submarine know-how and advanced fighter jets in return for supplying Russia with munitions, personnel and even food and oil for its war in Ukraine.
In March, North Korean state media published photographs of Kim inspecting what it described as a “nuclear-powered strategic guided missile submarine.” However, details of its displacement and capabilities remain unclear.
Experts estimate the vessel could displace 5,000–7,000 tons and carry about 10 nuclear-capable missiles—posing a significant challenge for US and South Korean anti-submarine warfare in both the peninsula and the Taiwan Strait.
North Korea’s submarine project is highly likely to have relied on Russian assistance, as the former has never been able to produce compact naval reactors. If confirmed, Russia’s transfer would cross a red line by breaching the Nuclear Non-Proliferation Treaty (NPT). It would also likely trigger fresh sanctions against both countries, underscoring the deepening partnership sealed after Kim’s 2023 summit with Russian President Vladimir Putin.
However, North Korea’s nuclear missile submarine program has stirred skepticism, with questions about its plausibility and actual capabilities. While the vessel could provide second-strike capability, doubts persist—from flawed Romeo and Golf-class retrofits to noisy propulsion that leaves it exposed to anti-submarine warfare (ASW).
North Korea may pursue hybrid propulsion—conventional with auxiliary nuclear reactors—but this has historically underperformed. Range and endurance remain constrained, limiting reach beyond regional waters.
With these limitations, North Korea’s nuclear missile submarine program looks more aspirational than functional, its deterrent value undercut by flaws and propaganda. Still, North Korea has a strong reason to pursue it.
North Korea has previously touted sea-based nuclear capability aboard its Amnok-class corvettes and may plan to arm its new Choe Hyeon-class destroyers with the same capability.
Surface warships are vulnerable compared to submarines, which may explain the country’s push to acquire nuclear missile submarines. However, it is unlikely that North Korea’s plans to get such will materialize without a substantial degree of Russian assistance.
While cooperation between North Korea and Russia was initially framed as a pragmatic and transactional relationship, Edward Howell says in a December 2024 Chatham House report that the increasing scale of collaboration, from troop deployments and arms-for-cash-and-energy deals to possible nuclear technology transfers, shows a shift toward a long-term strategic and ideological partnership.
Underscoring Howell’s points, the June 2024 North Korea-Russia Treaty on Comprehensive Strategic Partnership implicitly emphasizes both countries’ opposition to the Western-led international order in favor of a multipolar international system.
Howell also notes that China will be monitoring the development of the North Korea-Russia relationship, paying attention to increased bilateralism or trilateralism between the US, Japan and South Korea, with China being a key partner of both North Korea and Russia.
Underscoring the confluence between the latter autocratic powers, Chinese President Xi Jinping, alongside Putin and Kim, met during the 80th anniversary of the end of World War II in Beijing, presenting a symbolic statement of alignment. Yet China also has reason to avoid unchecked escalation, wary that nuclear proliferation on its doorstep could undermine its own security and influence.
But in contrast to the increasing ties between the latter autocratic powers, Politico reported this month that the upcoming US National Defense Strategy (NDS) prioritizes homeland defense and the Western Hemisphere over countering near-peer adversaries abroad.
Politico mentions mounting military tensions between the US and Venezuela as an indicator of this re-emphasis in US strategy. The report highlights that the upcoming NDS and supporting documents stress US allies’ increased responsibility for their own security as the US consolidates its efforts closer to home.
The report states that a change in US strategy may have a significant impact on the US troop presence in the Middle East and Europe, citing the defunding of the Baltic Security Initiative, which has helped Lithuania, Latvia, and Estonia build up their defenses against a possible Russian incursion.
Delving into the larger strategic impact of this possible US retrenchment, Kira Coffey and Ryan Fitzgerald point out in a February 2025 article for Global Defense Review that middle powers are coming to realize that security guarantees from a nuclear power only go as far as the latter’s national interests.
Coffey and Fitzgerald note that Ukraine’s search for stronger security guarantees, i.e., “nukes or NATO,” could prompt others in a similar situation to reevaluate the US’s security guarantees, potentially viewing the US as having waning political interest and resources to compete with near-peer adversaries in a multipolar world.
Should the US follow this course of retrenchment, the implications for the Indo-Pacific would be no less profound.
As Naoko Aoki points out in a February 2025 article for the National Bureau of Asian Research (NBR), while North Korea won’t attempt a forcible takeover of South Korea in the future, it could be emboldened to use limited military means and nuclear threats to ensure the survival of the Kim dynasty.
In response to potentially increased North Korean belligerent behavior, Lami Kim mentions in an April 2025 article for the Center for Strategic and International Studies (CSIS) that South Korea could be pushed even closer to getting nuclear weapons, as the US Trump administration softens its stance on North Korea. Japan may follow suit, but Junjiro Shida mentions in an April 2025 Politico article that, in contrast to South Korea, its nuclear taboo is still strong.
However, Politico points out that Japan and South Korea are longtime rivals, with Shida saying that Japan has more capability to develop nuclear weapons thanks to its 64 nuclear power plants and substantial plutonium reserves.
Taiwan may also join the nuclear bandwagon, with Politico noting that the self-governing island has been cited twice by the International Atomic Energy Agency (IAEA) for suspicious activity involving nuclear material. The report states that the ongoing threat of a Chinese invasion and US pressure to strengthen indigenous defenses could revive interest in nuclear arms.
North Korea’s murky nuclear missile submarine gamble and Russia’s clandestine backing could ignite a new arms race across East Asia. If US retrenchment deepens, the region may answer not with restraint but with its own nuclear ambitions.
