South Korea’s debate over underwater power is often framed within overly narrow terms. While the issue of acquiring nuclear-powered submarines (SSNs) is treated as a prestige-driven ambition, unmanned underwater vehicles (UUVs) are portrayed as future-oriented platforms that could one day replace manned platforms. Nevertheless, such framing misses the crucial strategic reality that Seoul is now facing. The challenge is no longer how to optimize underwater capabilities postulating a single contingency on the Korean Peninsula, but how to manage simultaneous and mutually reinforcing threats: this includes North Korea’s emerging sea-based nuclear ambitions, the growing probability of a Taiwan contingency that could strain allied naval assets, and the expanded Russian naval presence in the Western Pacific thanks to the gradual opening of the Northern Sea Route (NSR).
Under such an environment, it is unnecessary to choose between SSNs and UUVs. What is needed is a force structure and operational concept that deliberately integrate these two systems.
North Korea’s pursuit of a survivable second-strike capability at sea is uneven but persistent. Although Pyongyang has struggled due to technological and industrial constraints, it has made clear that SLBMs are the core element of its long-term deterrence narrative. Although North Korea’s ballistic submarine program remains immature at this juncture, its progress is undeniable. Even a limited and relatively unreliable SLBM capability could impose substantial strategic costs by forcing constant tracking efforts and compounding complexity in South Korea’s and its allies’ crisis management capabilities.
This problem becomes more acute when placed in a larger geographical context. If a serious crisis erupts in the Taiwan Strait, U.S. and Japanese high-end naval assets—especially those assigned to anti-submarine warfare (ASW), ISR, and long-range strike missions—would be rapidly absorbed. In such circumstances, North Korea does not need to commence an all-out war in order to secure leverage. Limited deployment of submarines, SLBM demonstrations, or maritime coercion alone would be sufficient to stretch South Korea’s defense mechanisms, delay allied reinforcement, and divert allied attention. The undersea domain is well suited for these types of strategic distractions.
At the same time, Russia’s Arctic strategy is increasingly and directly intersecting with Northeast Asia’s security. As the NSR becomes navigable—due to the impact of climate change—Moscow has both economic and military incentives to normalize its naval movements between its Northern and Pacific Fleets. This does not imply an immediate Russian naval threat vis-à-vis South Korea. Nonetheless, it does mean that a greater Russian presence in the region would likely make the undersea operational environment in the Western Pacific more congested, complex, and strategically ambiguous. For countries like South Korea, whose trade and security heavily depend on maritime stability, such ambiguity is far from ignorable.
Against this backdrop, SSNs offer capabilities that South Korea’s existing diesel-electric submarines cannot fully replace. Nuclear propulsion enables sustained speed, endurance, and operational flexibility that would be particularly important in multiple crisis circumstances. SSNs could be swiftly redeployed, remain on station for extended periods, and operate in broader theaters without the vulnerabilities associated with snorkeling and frequent port calls. Under a dual contingency scenario, such attributes would function as a hedge against allied overburden, rather than a symbol of prestige. While U.S. underwater assets are tied down elsewhere, South Korea does not have the luxury of belatedly recognizing that it lacks the independent capacity to secure its sea lines of communication (SLOCs).
Yet the cost and constraints of SSNs are also obvious. Modern nuclear-powered submarines are among the most expensive and production-constrained military platforms in the world. Even for the United States, procurement bottlenecks and shortages of an experienced workforce have become chronic. For South Korea, this implies that SSNs—if pursued—would be operated in limited numbers and would take a long time to be fielded. In sum, SSNs alone cannot be the sole solution for underwater deterrence.
This is where UUVs change the strategic equation. The Russo-Ukrainian war showcases that relatively inexpensive and expendable unmanned maritime systems could threaten high-end manned assets in ways that conventional planning has often underestimated. In December 2025, Ukrainian authorities claimed to have struck a Russian Kilo-class submarine that was stationed inside the Novorossiysk naval base. While Russia disputed the extent of the damage, the broader implication was unmistakable: submarines are often most vulnerable not at sea, but in port, during maintenance cycles, or while transiting predictable chokepoints.
For South Korea, the lessons from this case are direct. Any North Korean SLBM capability would rely on protected coastal waters, support infrastructure, and identifiable basing patterns. UUVs—which are combined with intelligence assets, underwater sensors, and special operations planning—offer a way to hold North Korean submarines at risk before they can create strategic unpredictability at sea. Unlike manned platforms, UUVs can be mass-produced, deployed in a sustained manner, and accepted as expendable. They also operate in gray areas that complicate attribution and escalation, which is strategically useful in deterrence dynamics.
Therefore, the most effective underwater posture for South Korea is a multilayered structure. SSNs would be in charge of the outer layer: they would provide blue-water endurance, advanced ASW capabilities, and the ability to operate across theaters during a dual contingency scenario. Meanwhile, UUVs would form the inner layer: this includes persistent surveillance in coastal waters, monitoring of submarine bases, deception operations, mine countermeasures, and precision targeting—if policy permits—of submarines at their most fragile moments.
Even from a cost-benefit perspective, such a division of labor is appealing. A single SSN represents billions of dollars in investment and decades of maintenance commitments. In contrast, UUV assets could be rapidly and repeatedly developed, customized for specific missions, and churned out with substantially lower price tags per unit. Recent international cases—including European interest in large autonomous submarines—illustrate that UUV technologies are increasingly becoming modular and accessible, while SSNs remain scarce and politically sensitive platforms.
The strategic integration of SSNs and UUVs would enable South Korea to respond to multiple threats without overcommitting to any single platform. SSNs would alleviate the danger of Seoul being left exposed during a Taiwan contingency while enabling independent undersea operations at range. Meanwhile, UUVs would raise the costs of maintenance, sortie generation, and basing by imposing continuous pressure on North Korea’s nuclear ambitions at sea. Once these two aspects are combined, the probability of an opponent implementing a simultaneous strategy—exploiting a crisis in one theater in order to enable aggression in another—would be notably reduced.
The underwater domain is no longer a theater reserved for a handful of great powers. It is transforming into a congested and crowded space where endurance, scale, and adaptability are becoming as important as platform performance. For South Korea, the key question is not whether SSNs or UUVs are the “future.” Instead, the future lies in designing a doctrine that allows these systems to complement each other’s limitations, creating underwater deterrence and resilience sufficient to function even when multiple crises occur simultaneously.
[Header image: Defense Acquisition Program Administration’s public work is used according to Korea Open Government License (KOGL) (KOGL Type 1 or KOGL Type 1), via Wikimedia Commons]
The views and opinions expressed in this article are those of the author.
Dr. Ju Hyung Kim currently serves as the president at the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly. He has been involved in numerous defense projects and has provided consultation to several key organizations, including the Republic of Korea Joint Chiefs of Staff, the Defense Acquisition Program Administration, the Ministry of National Defense, the Korea Institute for Defense Analysis, the Agency for Defense Development, and the Korea Research Institute for Defense Technology Planning and Advancement. He holds a doctoral degree in international relations from the National Graduate Institute for Policy Studies (GRIPS) in Japan, a master’s degree in conflict management from the Johns Hopkins University School of Advanced International Studies (SAIS), and a degree in public policy from Seoul National University’s Graduate School of Public Administration (GSPA).
