Nuclear Submarine Gamble by South Korea Could Trigger Underwater Arms Race in Asia

Seoul’s plan to build nuclear-powered attack submarines with US help is reshaping Asia’s security map, raising fears of an underwater arms race involving China, North Korea, Japan and India.​

A New Underwater Front in Asian Security

South Korea’s decision to push ahead with nuclear-powered submarines, backed by US technology and shipbuilding cooperation, is emerging as one of the most consequential military shifts in Asia in years. Seoul argues the move is essential to counter North Korea’s growing submarine-launched nuclear threat and China’s expanding undersea fleet, but analysts warn it could ignite a broader underwater arms race across the region.​

The plan follows a US policy reversal that for the first time allows South Korea access to nuclear propulsion technology, positioning the country to join the small club of states operating nuclear-powered submarines. Neighbours including China, North Korea and Japan are watching closely, with reactions ranging from quiet concern and condemnation to renewed debate about acquiring their own nuclear-powered boats.​

South Korea and US Advance Nuclear Submarine Deal

In late October 2025, US President Donald Trump signalled Washington would support South Korea in developing nuclear-powered attack submarines, shifting from earlier US reluctance to share such sensitive technology. The announcement was followed in mid‑November by a broader economic and defence package in which Seoul pledged large-scale investments in US industry while receiving approval to pursue nuclear propulsion for its navy.​

South Korean President Lee Jae-myung has framed the deal as both a strategic and economic partnership, linking tariff relief on Korean exports to long‑term cooperation in shipbuilding, nuclear energy and advanced defence platforms. A US fact sheet and South Korean media reports indicate Washington has relaxed restrictions on uranium enrichment and spent fuel reprocessing for propulsion use, steps that had long been blocked under past bilateral nuclear agreements.​

Key elements of the US–South Korea submarine deal

What the Nuclear Submarine Program Involves

South Korean officials and retired naval officers say the country has already advanced basic design work for nuclear-powered submarines, despite past delays and political hesitations. According to public comments cited in local defence reporting, the government estimates it will take around a decade to deliver the first operational boat and suggests a minimum fleet of four 5,000‑tonne nuclear-powered attack submarines is required.​

Defence Minister Ahn Gyu-back has described reactor assembly work as being at a significant stage, indicating that nuclear engineering and shipyard planning are moving in parallel. However, President Lee has also publicly cautioned that building such submarines remains extremely difficult, citing the financial, technical and regulatory challenges involved.​

Outline of South Korea’s planned nuclear submarine capability

Why Seoul Says It Needs Nuclear Submarines

South Korea argues that nuclear propulsion is vital to track North Korea’s emerging nuclear-armed submarines and to follow Chinese vessels that can already operate for long periods in the East and South China Seas. Diesel-electric submarines must regularly surface or snorkel to recharge batteries, limiting how long they can shadow adversaries or remain hidden in distant waters.​

North Korea has unveiled images and reports of a nuclear-powered, nuclear‑armed submarine under construction, and has tested submarine‑launched ballistic missiles (SLBMs), steps that South Korean officials say significantly raise the threat level. Seoul insists its own nuclear-powered submarines would carry only conventional weapons and that the country has no intention of developing a domestic nuclear arsenal, reiterating commitment to the Nuclear Non‑Proliferation Treaty (NPT).​

Drivers behind South Korea’s nuclear submarine push

Regional Reactions: From Alarm to Quiet Support

North Korea has condemned the South’s nuclear-powered submarine plan as a dangerous escalation, warning it could set off a nuclear domino in the region and deepen a global arms race. The North’s rhetoric builds on its own undersea nuclear developments, which outside analysts already view as a major driver of military competition on and under the Korean Peninsula.​

China’s official response has so far been relatively muted compared with its sharp criticism of the AUKUS nuclear submarine deal for Australia, but Chinese commentators and state-linked analysts warn the move could erode non‑proliferation norms and destabilize regional security. At the same time, some Japanese security experts see South Korea’s nuclear submarines as a potential counterweight to China and as an opportunity for deeper trilateral undersea cooperation with the United States.​

Snapshot of regional reactions

Rising Fears of an Underwater Arms Race in Asia

Analysts warn that South Korea’s entry into the nuclear-powered submarine club, alongside existing operators like China and India and Russia’s regional deployments, risks triggering a multi-sided undersea arms race in Asia. China already operates a growing fleet of nuclear-powered attack and ballistic missile submarines, while India is expanding its Arihant‑class strategic submarines and preparing to commission additional nuclear boats.​

Several recent studies and commentaries argue that the combined effect of North Korea’s new atomic submarine, Chinese undersea modernization, India’s nuclear fleet expansion and South Korea’s SSN program could push other states, including Japan, further toward considering nuclear propulsion. Some security experts describe this as a shift from a primarily surface‑ and air‑based competition to a more opaque underwater contest where detection is harder and miscalculation risks are higher.​

Existing and emerging nuclear-powered submarine players in Asia

Legal, Technical and Political Hurdles

Despite the momentum, South Korea faces serious obstacles. Building, operating and safely maintaining nuclear-powered submarines requires long-term investment in specialized reactors, fuel handling, safety regulation and crew training, areas where even experienced navies have encountered setbacks. Experts note that cost overruns and engineering delays are common in nuclear naval programs, raising questions about whether Seoul can meet its ambitious timelines.​

Non‑proliferation advocates are also watching closely. While the NPT does not explicitly ban naval nuclear propulsion, transferring weapons‑usable nuclear material for submarine fuel can blur lines in the safeguards system and create precedents other countries might seek to exploit. Some analysts warn that if multiple states in Asia seek NPT‑compliant submarine fuel arrangements simultaneously, verification burdens on the International Atomic Energy Agency could grow sharply.​

Key challenges facing South Korea’s nuclear submarine project

What Comes Next for the Region

South Korean officials stress that their pursuit of nuclear-powered submarines is not intended to fuel an arms race and that the vessels will remain conventionally armed, but neighbouring states remain wary. As design work proceeds and reactor and shipyard milestones are reached, regional diplomacy and crisis‑management mechanisms are likely to come under greater strain, particularly if more countries openly explore similar capabilities.​

For now, the train is already moving, as one retired South Korean naval officer put it, with governments across Asia recalibrating their defence plans in anticipation of a more crowded and more heavily armed undersea environment. Whether this nuclear submarine gamble ultimately strengthens deterrence or accelerates an underwater arms race in Asia will depend on how quickly capabilities grow—and whether diplomacy can keep pace.​