The decision will have major implications for the South Korea-U.S. alliance and beyond.

After his summit with South Korean President Lee Jae-myung on the sidelines of the 2025 APEC Summit in Gyeongju, South Korea, U.S. President Donald Trump announced that the United States has authorized South Korea to build nuclear-powered submarines (SSNs). The decision sent ripples across global strategic and non-proliferation circles.

In a social media post on October 29, Trump declared that the South Korea-U.S. alliance “is stronger than ever before and, based on that, I have given them approval to build a Nuclear Powered Submarine.”

In a separate post, he added, “South Korea will be building its Nuclear Powered Submarine in the Philadelphia Shipyards, right here in the good ol’ U.S.A.”

In these posts, Trump reframed one of the most sensitive defense-technology barriers in U.S. alliance policy – and did so in his typically public, unscripted manner.

Trump finally gave the U.S. seal of approval to a long-standing South Korean ambition: joining the elite club of nations operating SSNs. Washington had repeatedly resisted Seoul’s requests, however, citing non-proliferation constraints and the political sensitivity of transferring nuclear-propulsion technology.

Now, under Trump’s renewed “America First, Allies Invest” framework, the door appears open – but at what cost and consequence?

Strategic Logic: Strengthening Deterrence and Alliance Asymmetry

From Seoul’s perspective, SSNs represent a long-awaited strategic upgrade. Facing an increasingly sophisticated North Korean under-sea threat and a more assertive Chinese navy, South Korea has argued that nuclear propulsion is essential to ensure long-duration, stealthy patrols in the Indo-Pacific.

As Lee told Trump during their summit, “The diving capability of our conventional diesel submarines is limited, which restricts our ability to track North Korean or Chinese submarines.”

Unlike diesel-electric submarines, which must surface or snorkel to recharge batteries, SSNs can remain submerged for months – offering unmatched survivability and range.