Seoul reportedly preparing to announce a road map for its nuclear-powered submarine program, transforming what was once a long-held strategic aspiration into a more immediate political issue. Naval nuclear propulsion increases non-proliferation issues on fuel, safeguards and nuclear latency. But treating Seoul’s pursuit solely as a sign of hidden nuclear ambitions risks missing a larger question: whether a U.S. ally facing a rapidly nuclearizing North Korea can remain non-nuclear while believing it has sufficient means to defend itself.
This question has become more urgent as North Korea is growing not only its nuclear arsenal, but also the means by which it could deliver nuclear weapons. Pyongyang is trying to strengthen its maritime nuclear capabilities, and suspicions have increased. Russia has provided, or may provide, technology or materials to support North Korea’s nuclear submarine program. In such an environment, simply telling South Korea what it should not do is unlikely to be enough. The more difficult question is how South Korea can strengthen its deterrence while remaining non-nuclear.
In fact, Seoul has long had its own answer to this question. He continued what could be described as “conventional sufficiency“, a logic that seeks to enforce nonproliferation norms while deterring North Korea through U.S. extended deterrence and South Korea’s own conventional strategic capabilities. This adds further explanation as to why South Korean foreign policy elites have remained relatively cautious about nuclear weapons despite continued public support for an independent nuclear arsenal. His caution reflects the diplomatic, economic and alliance costs of nuclear weapons. But it also relies on a consistent internal belief that South Korea can remain non-nuclear if its conventional deterrence remains credible. This logic was supported by investments in military capabilities designed to make North Korean nuclear use costly, risky, or unlikely to succeed.
Seen in this light, nuclear-powered submarines could strengthen rather than weaken the logic that South Korea would not pursue nuclear weapons. They would not completely 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 deterrence posture more credible and politically sustainable.
This is also why calls on South Korea to tone down elements of Kill Chain are so difficult to accept in Seoul. Kill the channel is South Korea’s conventional strategy for detecting signs of an imminent North Korean attack and striking key targets before that attack can be carried out. The argument for restraint is that such capabilities could increase North Korea’s fear of having to resort to nuclear weapons at the start of a crisis or losing them. This concern is understandable. But Kill Chain isn’t just a military option. This is part of the political and strategic justification for the claim that South Korea can deter North Korea without nuclear weapons. Asking Seoul to scale back its measures might seem, no matter how strong the South Korea-U.S. alliance is, like asking the country to rely almost entirely on external guarantees for its own security.
This is the paradox at the heart of the problem. If Seoul is urged not to acquire nuclear weapons, but also discouraged from developing the advanced non-nuclear capabilities it deems necessary, the domestic case for nuclear restraint becomes more difficult to sustain. Kenneth Waltz’s observation Helpful here is the fact that external opposition is rarely the most decisive factor in preventing a state from going nuclear. The point is not that South Korea is doomed to go nuclear. The reason is that nonproliferation is stronger when restraint is politically sustainable, not just externally demanded. If Washington and the broader nonproliferation community want South Korea to remain non-nuclear, it may be worth asking whether opposition to Seoul’s nuclear submarine campaign is primarily a proliferation problem might actually weaken the case for restraint. Some forms of allied capacity building can actually help support nonproliferation by making nonnuclear deterrence more credible.
This does not mean that South Korea should receive a blank check. A nuclear-powered submarine program should be handled with exceptional care, including a clear reaffirmation of Seoul’s commitment to the Non-Proliferation Treaty, greater transparency on nuclear fuel and safeguards, and a clearly defined military objective. But viewing efforts to make South Korea’s non-nuclear deterrent more credible as proliferation concerns could end up weakening the restraint that nonproliferation policy is meant to preserve. Nonproliferation is best served when restraint is something a state can confidently maintain, not just something it is asked to accept.