How To Enhance South Korea’s Conventional Deterrent
North Korea’s nuclear and missile program continues to advance. Most worryingly, these capabilities will likely be deployed in pursuit of the North’s declaratory doctrine of pre-emptive nuclear escalation. The U.S.-South Korean alliance now has to cope with the possibility of North Korea using tactical nuclear weapons in order to achieve military or political objectives without triggering American nuclear retaliation.
South Korea’s response for the last decade has been its ambitious conventional force development plan, known as the Three-Axis System. This focuses on both precision strikes and intelligence, surveillance, target acquisition, and reconnaissance. With the lifting of bilateral missile guidelines, Seoul’s efforts to develop ballistic missile and space-based intelligence, surveillance, and reconnaissance capabilities are now in full swing.
To make the most of these efforts, South Korea should focus on improving the survivability and reliability of its conventional strike capabilities by investing more in passive defense. These assets provide a crucial means of retaliating against North Korea’s limited nuclear employment and imposing costs on the leadership in Pyongyang. As such, enhancing their survivability would yield many benefits for both South Korea and the U.S.-South Korean alliance.
Complicating North Korea’s Calculus
Conventional precision strikes represent the most readily-available option for responding to North Korean limited nuclear use while minimizing the risk of escalation. They could be used to destroy hard and deeply buried targets, making them attractive for striking regime assets within cities. This is particularly important as U.S. political leaders could be hesitant to use tactical nuclear weapons against urban targets.
Hence, for Seoul, improving the survivability and reliability of its massive conventional strike capabilities should be the key strategic goal. These non-nuclear strategic weapon systems — not to mention U.S. forward-deployed assets in the region — present a difficult operational and strategic problem for North Korea. Seoul’s increasing number of missiles and growing variety of platforms increase the risk of immediate retaliation for Pyongyang. Their enhanced survivability would ensure North Korea faces serious costs should they decide to escalate.
Making South Korea’s conventional assets more survivable would also discourage North Korea from contemplating a “bolt out of the blue” attack to disarm the South Korean and the U.S. forces in the region. As such, in addition to improving the Korean Air and Missile Defense to protect its key strike assets, targeting capabilities, and other supporting facilities, South Korea should also invest more in passive defense measures, an area that Seoul has traditionally paid less attention to. Of particular importance is making its command, control, communications, computers, intelligence, surveillance, and reconnaissance — as well as other critical national infrastructure such as energy and communications — more redundant and resilient. The North has threatened to strike these facilities. Civil defense drills, recently conducted for the first time in six years, should be strengthened and held more routinely.
Military planners should also adopt the optimal combination of passive defense tactics for countering missiles, including hardening, dispersion, and deception. The U.S. and Korean air forces are already experimenting with dispersion to adapt to the changing operational environment. As the land-based Hyunmoo-series missiles are road-mobile, South Korea’s Army Strategic Missile Command could apply similar tactics to increase survivability while maintaining the operational readiness of its missile force. Seoul should increase the number of mobile missile launchers to this end.
These small tactical matters would complicate the military calculus for North Korea, which still faces significant resource constraints, and add to the overall deterrent effects of the alliance’s combined defense posture. North Korea undoubtedly follows the measures implemented by the United States and South Korea and the joint drills conducted to prepare for a nuclear contingency scenario. When coupled with Seoul’s multi-layered missile defense system and the U.S. theater missile defense assets, passive defense tactics could significantly reduce the likelihood of success and the potential benefits of nuclear use for North Korea while also raising the costs. Passive defense tactics are particularly valuable because many experts question the feasibility of using offensive counter-missile operations to deny North Korea’s first use of weapons of mass destruction and worry about the implications for crisis stability.
Deterrence and Insurance
From the broader strategic and political perspective, Seoul’s possession of a reliable conventional means of cost-imposition on the North Korean leadership is also an insurance policy. Despite the various institutionalized mechanisms for nuclear consultation for the U.S.-South Korean alliance, the most fundamental fact has not changed: Nuclear employment ultimately requires “explicit authorization of the President of the United States.” And while there is certainly a belief that nuclear use should be met with nuclear use, if U.S. political leaders were presented with a menu of options in response to a North Korean strike, they might still prefer to minimize collateral damage. This could be especially true for the Biden administration, which emphasizes non-nuclear means of deterrence. As a result, planners have an incentive to present conventional options to achieve the desired damage.
As an ally, Seoul should also hedge against unpredictability in American nuclear policy. Political support for nuclear consultation may not continue beyond the Biden administration. In this light, former National Security Advisor Kim Sung-Han has noted that the next 18 months represent a “golden time” for making substantive progress on extended nuclear deterrence. Moreover, while the United States has incrementally increased deployment of low-yield nuclear weapons in recent years, the capability remains limited, and America faces constraints in their employment. The heated debate over nuclear-armed sea-launched cruise missiles reflects this division within the U.S. expert community and the lack of clarity in the future direction of American policy. For South Korea, advanced conventional weapons can help to fill this gap.
Conversely, in the face of growing great-power competition and breakdown of arms control, Seoul may eventually find Washington pushing for forward deployment of land-based missiles that have a range beyond that needed for North Korea. Future U.S. administrations could even try an abrupt nuclearization of the alliance through steps like building storage sites for American tactical nuclear weapons in South Korea. Though these scenarios seem less likely today, regional and global trends suggest that they may not be in the future. They would pose difficult domestic political challenges for South Korean leaders even though they have previously sought such measures, just as they did for European NATO allies during the Cold War. Seoul’s advanced conventional strike capabilities would place South Korean leaders in a better bargaining position when faced with these potential changes in American policy.
South Korea’s Best Option
It is important to recognize that the U.S. nuclear umbrella is still the ultimate guarantor of security for South Korea today. Washington should ensure that Seoul has a meaningful role in American nuclear planning, decision-making, and employment to enhance the effectiveness of extended nuclear deterrence. Otherwise, calls for redeployment of American tactical nuclear weapons or an indigenous nuclear deterrent will quickly regain traction in Seoul. It remains the case that many in South Korea regard nuclear hedging as the only effective hedging strategy to adopt.
However, after South Korea reaffirmed its commitment to nonproliferation in the Washington Declaration, Seoul’s best course of action today is to focus on improving the survivability and reliability of the advanced conventional strike capabilities it has already invested heavily in. To do so, it should continue to upgrade tactical defensive measures and devise creative ways of employing them in response to limited nuclear use by North Korea.
As it is operationalized today, deterrence draws from a continuous spectrum of capabilities, both nuclear and non-nuclear, as well as kinetic and non-kinetic. In this sense, Seoul is already contributing greatly to the “combined deterrence and response posture” vis-à-vis a nuclear North Korea. South Korea can continue to expand this contribution.
Shifting focus to non-nuclear strategic weapons will have many other benefits for Seoul. It could help to manage expectations — both among elites and the public — about extended nuclear deterrence and improve alliance cohesion. Focusing on survivability would help to allay American concerns about entrapment, contribute to strategic stability by limiting pathways to inadvertent nuclear escalation, and allow South Korea to maintain agency in shaping the combined defense posture in the future. Seoul should embrace this path to a stronger and more survivable non-nuclear deterrent.
Jung Jae Kwon is a Stanton Nuclear Security Research Fellow at the Project on Managing the Atom and the International Security Program of the Harvard Kennedy School’s Belfer Center for Science and International Affairs. He is also a doctoral candidate at the Massachusetts Institute of Technology’s Department of Political Science and Security Studies Program.
