The recent agreement between South Korea and the United States regarding the development of a nuclear-powered submarine has sparked intense debate at home and abroad.

Some hail the decision as a long-awaited milestone, arguing that it strengthens South Korea’s deterrence posture against North Korea’s nuclear threat and signals that Seoul is finally acquiring the prestige of a major power. Others, however, warn that it may look like a step toward nuclear proliferation, undermining decades of Korea’s commitment to non-nuclear principles.

Yet both sides tend to rely on a misleading assumption that South Korea is moving toward its own nuclear armament. That assumption is, however, both premature and inaccurate. Seoul’s plan to develop a nuclear-propulsion submarine does not mean it is seeking nuclear weapons. It reflects a recognition that diesel-powered submarines are insufficient to meet the demanding missions in surrounding waters, especially the East Sea, where depth and submarine activity by neighboring states require longer endurance and stealthier platforms.

It is crucial to understand the distinction between an SSN and an SSBN. An SSN, or “Submersible Ship, Nuclear-propulsion,” is designed for conventional missions using nuclear power solely for propulsion. In contrast, an SSBN, or “Submersible Ship, Ballistic-missile, Nuclear-propulsion,” carries submarine-launched ballistic missiles armed with nuclear warheads. The difference is not semantic, but it is strategic. Korea seeks an SSN, not an SSBN. Confusing the two words leads to unnecessary alarmism and distorts the actual intent of Korea’s defense policy of not pursuing independent nuclear armament.

Why is Seoul unlikely to pursue nuclear armament? The answer lies in three layers of reasoning: strategic, diplomatic and ethical. Strategically, nuclear armament would impose unbearable costs to Seoul. It would breach the Nuclear Non-Proliferation Treaty and invite sweeping international sanctions. Korea would, in effect, be following the same path North Korea took, sacrificing its global reputation and economic prosperity. Such a move would shatter trust in the Korea-US alliance and its credibility within the global non-proliferation regime — a linchpin and cornerstone of Korea’s diplomacy for longer than seven decades.

Diplomatically, it would destroy the diplomatic leverage that Seoul currently enjoys in urging Pyongyang to abandon its nuclear program. Once South Korea chooses the nuclear path, it loses the legitimacy to call for denuclearization in North Korea. It would also give the other countries a convenient justification to defend North Korea’s nuclear program, weakening international unity on sanctions and leaving the peninsula more unstable than before. Japan, too, would likely respond by accelerating its own military normalization, triggering a regional arms race — precisely the kind of spiral Korea’s cautious diplomacy has long sought to prevent.

Ethically, nuclear weapons run counter to the universal pursuit of the common good. Their destructive power goes far beyond any proportionate need for defense. They do not secure peace and prosperity; they impose fear and insecurity. From the standpoint of human civilization, the ultimate goal should be the complete abolition of nuclear weapons. Therefore, any new move toward nuclear armament contradicts that collective mission. For an advanced democracy like South Korea, moral leadership is as valuable as military power. To protect peace through restraint, not escalation, is a higher form of strength.

Still, one cannot dismiss the reality that the threat from Pyongyang is grave. North Korea openly declares that it is building a nuclear-powered submarine capable of launching nuclear missiles, and its record suggests that such declarations often materialize. For South Korea, assuming that North Korea will possess a nuclear-armed submarine is not paranoia — it is a logical response. In this context, pursuing a nuclear submarine without nuclear weapons is a rational and defensive measure, not an aggressive one.

Seoul’s choice aligns with the concept of extended deterrence under the Korea-US alliance. The United States guarantees that its nuclear umbrella and strategic assets will deter any North Korean attack. Yet the effectiveness of that deterrence depends on mutual trust and coordination. If that trust wavers, anxiety within the Korean public inevitably rises. Hence, South Korea’s efforts to strengthen its conventional deterrence capabilities — through advanced missile systems, air defenses and nuclear-powered submarines — complement, rather than contradict, the alliance. Extended deterrence must rest on both alliance commitment and self-reliant capability; one reinforces the other.

The East Sea, famous for its deep waters and complex undersea geography, is an arena where nuclear-powered submarines from regional powers including the US, China and Russia, frequently operate. For the Republic of Korea Navy, monitoring and tracking these movements is an essential task. Nuclear propulsion allows longer patrols without surfacing, ensuring both survivability and strategic awareness. Considering North Korea’s ambitions and the growing presence of foreign nations’ fleets, the rationale for Korea’s SSN project is both legitimate and urgent. Technically, nuclear propulsion does not mean nuclear armament; the reactor provides energy, not warheads. The distinction must be understood and communicated precisely to prevent misunderstanding.

If neighboring states nonetheless harbor concerns about proliferation, South Korea should respond with transparency and diplomacy. Effective communication will be vital to preventing misunderstanding. Domestically, the government must also manage its narrative with care. Some citizens might mistakenly equate nuclear propulsion with nuclear armament, assuming that the Lee Jae Myung administration is pursuing an independent nuclear path. That misunderstanding, if echoed abroad by civic groups or media, could jeopardize not only the submarine project but also Korea’s long-term goals of securing greater flexibility in nuclear fuel reprocessing and uranium enrichment in terms of industrial necessity.

Ultimately, this debate is about more than hardware. It is about how a responsible middle power navigates the delicate balance between security needs and global norms. The distinction between SSN and SSBN encapsulates that challenge. Recognizing the difference between propulsion and proliferation, deterrence and destruction, is key to understanding South Korea’s choice. Korea’s pursuit of an SSN marks not an arms race, but an evolution toward smarter defense — anchored in alliance, transparency and moral responsibility.

Wang Son-taek

Wang Son-taek is an adjunct professor at Sogang University. He is a former diplomatic correspondent at YTN and a former research associate at Yeosijae. The views expressed here are the writer’s own. — Ed.

khnews@heraldcorp.com