The announcement that The US will help South Korea build nuclear ‘attack’ submarines marks a major shift in defence cooperation between the two countries and signals a new phase of military strategy in East Asia. The White House confirmed that Washington has granted approval for Seoul to begin building nuclear-powered submarines and will work closely with South Korea to secure fuel and meet technical requirements. The move comes at a time of heightened military competition and growing pressure from North Korea and China.
The submarine partnership follows a recent trade agreement between the two nations, in which Washington reduced tariffs from 25% to 15% in exchange for South Korea’s commitment to invest $350bn in the US economy. According to US officials, the submarine decision reflects a deeper security alignment and a recognition of evolving threats in the region.
In a statement released Thursday, the White House said the US had approved “nuclear-powered attack submarines” for the Republic of Korea and would help advance the project, including fuel arrangements. Former President Donald Trump also posted on Truth Social that the vessels would be built at a Philadelphia shipyard run by South Korean conglomerate Hanwha, although South Korean officials later questioned whether that facility has the capacity to construct such advanced ships.
Only a handful of countries — the US, Russia, China, France, the UK and India — currently operate nuclear-powered submarines. South Korea’s existing fleet of around 20 submarines is diesel-powered, requiring frequent surfacing. Nuclear-powered vessels can travel farther, faster, and with far greater stealth.
Why Seoul Wants Nuclear-Powered Submarines
Seoul’s push for nuclear-armed submarines is driven primarily by North Korea’s expanding military ambitions. Pyongyang recently revealed that it is pursuing its own nuclear submarine programme and released images showing Kim Jong Un inspecting one under construction. South Korean President Lee Jae Myung told Trump at the APEC summit that Seoul required nuclear-powered vessels to counter the North’s growing maritime and nuclear threats.
South Korea’s Defence Minister Ahn Gyu-back said last week that the new submarines would represent a milestone in national defence and would provide a major strategic upgrade. Greater stealth, he argued, would make it harder for North Korea to predict or track South Korean naval movements — a change that would “keep Kim Jong Un awake at night.”
Experts say the development is also part of a wider regional arms race. Jo Bee-yun of the Sejong Institute noted that North Korea’s nuclear arsenal, which is estimated at around 50 warheads, has already reshaped the security dynamics in East Asia. South Korea’s acquisition of nuclear submarines, she added, reflects a response to long-term regional tension.
North Korea’s Nuclear Submarine Ambitions
North Korea’s own submarine programme has accelerated in recent years. South Korean officials believe Pyongyang may be receiving assistance from Russia. Images released in March 2025 showed a submarine Pyongyang claimed to be nuclear-powered, with Kim Jong Un personally inspecting the vessel.
Analysts warn that North Korea could field nuclear-powered submarines within a few years, adding another layer of unpredictability to the peninsula’s security environment. The advancement of South Korea’s nuclear submarine programme is therefore viewed as a necessary counterweight, even if it does not fundamentally shift the power balance.
Will the Agreement Escalate Regional Tensions?
While nuclear submarines offer strategic advantages, their high cost and long construction timeline mean they may have limited short-term impact. Dr Yang Uk of the Asan Institute for Policy Studies said the primary purpose of the plan is political — assuring South Korean voters that their government is responding decisively to North Korea’s nuclear threat. He also warned that Pyongyang may use Seoul’s new capability as justification for further expanding its own nuclear arsenal.
Jo Bee-yun argued that South Korea will still benefit strategically, as nuclear-powered submarines enable faster and longer deployments. They also enhance Seoul’s ability to operate alongside allied navies, giving the country a stronger regional role.
What the US Stands to Gain
For the United States, helping South Korea build nuclear submarines strengthens its regional influence while placing additional pressure on China and North Korea. Analysts suggest Washington wants Seoul to take on a more active defence posture, particularly as China expands its naval presence in the region.
According to Dr Yang, Trump has pushed more defence responsibility onto Seoul, knowing that South Korea is willing to increase its military spending. He said the arrangement effectively positions South Korea as a strategic partner in confronting Chinese and North Korean military expansion.
China’s government reacted with concern. Its ambassador to South Korea, Dai Bing, urged Seoul to act “prudently” and warned that the security situation remains “complex and sensitive.” Beijing has been increasing its activity near South Korea’s maritime borders, prompting further concern in Seoul and Washington.
What Happens Next?
Although Trump stated the submarines would be built in Philadelphia, South Korean officials insist construction must occur locally, where the country already has the advanced facilities required for such a programme. South Korea’s Prime Minister Kim Min-seok told parliament that the Philadelphia shipyard “did not have the capability” to build nuclear-powered submarines, raising questions about where final production will take place.
Hanwha, the shipyard’s owner, has not yet issued a formal statement.
The next major step is revising the nuclear cooperation agreement between the US and South Korea. This would allow the transfer of nuclear fuel and establish strict guidelines for how it may be used.
With the deal now formally approved, Seoul is entering a new strategic era — one in which nuclear-powered submarines may become central to its security planning and to its alliance with the United States.
