Asia Defense | Security | East Asia

South Korea’s Nuclear Submarine Push Is a Test of Non-nuclear Deterrence

Can Seoul strengthen deterrence while remaining non-nuclear?

Seoul is reportedly preparing to announce a roadmap for its nuclear-powered submarine program, turning what was once a long-running strategic aspiration into a more immediate policy question. Naval nuclear propulsion raises non-proliferation questions about fuel, safeguards, and nuclear latency. But treating Seoul’s pursuit only as a sign of hidden nuclear ambitions risks missing the larger issue: whether a U.S. ally facing a rapidly nuclearizing North Korea can remain non-nuclear while still believing that it has enough means to defend itself.

That question has become more urgent as North Korea expands not only its nuclear arsenal, but also the ways it might deliver nuclear weapons. Pyongyang is trying to strengthen its sea-based nuclear capabilities, and suspicions have grown that Russia has provided, or might provide, technologies or materials to support North Korea’s own nuclear-powered submarine program. In this environment, simply telling South Korea what it should not do is unlikely to be enough. The harder question is how South Korea can strengthen deterrence while remaining non-nuclear.

In fact, Seoul has long had its own answer to that question. It has pursued what might be labelled “conventional sufficiency,” a logic that seeks to uphold non-proliferation norms while deterring North Korea through U.S. extended deterrence and South Korea’s own strategic conventional capabilities. This adds an additional layer of explanation for why South Korea’s foreign policy elites have remained relatively cautious about nuclear armament despite persistent public support for an independent nuclear arsenal. Its caution has reflected the diplomatic, economic, and alliance-related costs of nuclear armament. But it has also rested on an internally coherent belief that South Korea can remain non-nuclear if its conventional deterrent remains credible. That logic has been backed by investments in military capabilities designed to make North Korean nuclear use costly, risky, or unlikely to succeed.

Seen this way, nuclear-powered submarines could strengthen rather than weaken the logic of South Korea not going nuclear. They would not fully remove South Korea’s vulnerability to North Korean nuclear weapons. But by improving endurance, survivability, and operational flexibility at sea, they could make Seoul’s non-nuclear deterrent posture more credible and politically sustainable.

This is also why calls for South Korea to tone down elements of Kill Chain are so difficult to........

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