How S Korea would respond to Taiwan hostilities

Despite being a key US regional ally, questions are rising about whether South Korea would take proactive measures if China were to initiate hostile actions against Taiwan?

Given its deep economic interdependence with China, South Korea finds itself strategically caught between Washington and Beijing.

To examine this issue, this writer conducted interviews last year with South Korean military officials in which I classified China’s potential hostile actions against Taiwan into three scenarios:

(1) gray zone operations, which include actions such as deploying China’s maritime militia and coast guard vessels to harass Taiwanese ships, thereby exerting pressure on Taiwan without directly provoking open conflict; (2) a naval blockade; and (3) a full-scale military invasion.

There was a strong consensus among the officials on how South Korea should respond if China were to initiate (1) gray zone operations, (2) a naval blockade, or (3) a full-scale invasion of Taiwan.

In all three scenarios, they agreed that South Korea should increase its alert level within the US-ROK Combined Forces and reinforce deterrence against potential North Korean provocations.

This concern stems from the possibility that North Korean leader Kim Jong Un, whether acting in coordination with China or independently, might view a regional shift in US military focus toward the Taiwan Strait as an opportunity to exploit a potential power vacuum on the Korean Peninsula.

To prevent such a miscalculation, it is essential to consistently signal to North Korean authorities that US-ROK contingency plans will function effectively as intended, eliminating any perception of nuclear decoupling between South Korea and the US.

Regarding military capability, South Korea should prioritize acquiring additional ground-to-ground precision missiles capable of penetrating underground bunkers, which would serve as critical assets for South Korea’s kill chain and Korea Massive Punishment and Retaliation (KMPR) strategies.

Apart from strengthening deterrence, South Korea’s response strategy varied across the three scenarios. In scenario one, where China engages in gray zone operations, most South Korean military officials recommended maintaining neutrality and avoiding actions that could unnecessarily provoke China, such as deploying naval vessels to the Taiwan Strait or providing logistical support to US forces in the region.

This cautious approach stems from South Korea’s economic interdependence with China and the expectation that any direct involvement could lead to significant economic retaliation, as evidenced by the backlash following the 2017 THAAD deployment.

Additionally, it is important to note that the 1953 US-ROK Mutual Defense Treaty primarily emphasizes the defense of South Korean territory against external threats, but does not contain provisions obligating South Korea to participate in military operations beyond its borders.

Meanwhile, in scenario two, where a Chinese naval blockade in the Taiwan Strait could disrupt South Korea’s sea lines of communication (SLOC), some officials suggested that South Korea should deploy naval forces to secure these critical trade routes, which are essential for economic stability.

To address this challenge, South Korea should acquire five to six Aegis-equipped naval vessels, each with a minimum capacity of 100 Battle Force Missiles (BFM)—a metric that represents the total number of missile cells on a naval vessel capable of launching both offensive and defensive missiles, serving as a standardized measure of a fleet’s overall missile firepower.

In this particular scenario, the focus would be on anti-ship missiles designed to target Chinese naval vessels. Under this framework, two to three ships could be stationed in the Taiwan Strait for extended periods, rotating between South Korean waters and the Taiwan Strait.

To effectively implement this strategy, South Korea should focus on developing a Blue Water Navy, capable of sustaining extended operations far from its shores.

This is particularly important because rerouting South Korea’s SLOCs away from the Taiwan Strait—through the Indonesian and Philippine archipelagos or around Papua New Guinea via the Solomon Sea—would be both time-consuming and costly.

In scenario three, some South Korean officials believed that, at a minimum, South Korea should provide logistical support to US forces in Korea deploying to the Taiwan Strait, such as access to South Korean airfields and fuel supplies for US Forces Korea (USFK).

Beyond logistical support, South Korea should also pursue the acquisition of five to six Aegis-equipped naval vessels, along with expanded ISR (Intelligence, Surveillance, and Reconnaissance) capabilities and an increased arsenal of precision-guided missiles.

However, this situation becomes significantly more complex if North Korea launches military aggression against South Korea at the same time that China invades Taiwan—indicating that deterrence against North Korea has failed.

If a two-front war scenario were to materialize, many South Korean military officials suggested that their military assets, along with key US Forces Korea (USFK) assets, should not be deployed to the Taiwan Strait. This position is understandable, considering the response I received from Japanese Self-Defense Force (JSDF) officials during my discussions in 2023.

When asked about Japan’s response in a two-front war scenario, JSDF officials stated that Japan would prioritize defending the Taiwan Strait, allocating approximately 60-70% of its air and naval assets to support US operations in the region, while only 30-40% would be reserved for Japan’s own defense.

This allocation would significantly impact Japan’s ability to operate under OPLAN 5055, a joint US-Japan military strategy designed to address potential contingencies on the Korean Peninsula in the event of a crisis involving North Korea.

Such a shift in Japan’s strategic focus could directly affect the joint US-ROK Operation Plan (OPLAN), which assumes that in the event of a North Korean invasion, South Korean and USFK would initially hold positions north of the Han River until reinforcements arrive from US Forces Japan (USFJ) within approximately two weeks.

Under this plan, the JSDF plays a critical role in supporting US military operations through logistical and operational assistance.

Given that the bulk of US reinforcements from the US mainland would take approximately 90 days to fully deploy—a timeline expected to overwhelm North Korean aggressors—the timely arrival of reinforcements from Japan is crucial in the early phase of the conflict.

If USFJ and Japan’s military assets are largely tied up in the Taiwan Strait, South Korea would have no choice but to allocate all of its own military resources to compensate for the reduced support from US forces in Japan, further complicating South Korea’s ability to contribute to regional security in Taiwan.

Overall, while it remains unclear whether the Trilateral Security Cooperation Framework (TSCF) has addressed South Korea’s specific action plans in a Taiwan contingency—as its detailed provisions remain classified—South Korea’s response to Chinese aggression across all three scenarios is unlikely to be highly proactive.

Instead, South Korea is expected to focus primarily on strengthening deterrence against potential North Korean military aggression rather than directly intervening in a Taiwan crisis.

This approach reflects the slightly different strategic priorities between South Korea and the US and Japan, as well as the limited availability of military assets in the region that all three countries must carefully allocate.

Given that these differences in strategic priorities could create challenges in a potential crisis—whether in a Taiwan contingency alone or a simultaneous Taiwan-Korean Peninsula conflict—it is crucial for the US, South Korea and Japan to develop a clear understanding of each country’s likely responses during a crisis.

By doing so, the three nations can work toward closing capability gaps and improving coordination before a major conflict arises.

Dr Ju Hyung Kim, CEO of the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly, is currently adapting his doctoral dissertation, “Japan’s Security Contribution to South Korea, 1950 to 2023,” into a book.