Think Tank: China's (J-20) Stealth Fighter Crosses the Korea Strait

In late July, China National Television broadcast footage of a elite air force regiment of the People's Liberation Army patrolling the Taiwan Strait and the Tsushima Strait/Korea Strait. The clip strongly implied that the (J-20) stealth fighter had crossed the narrow waterway between South Korea and Japan. Tokyo and Seoul have not publicly confirmed intercepting or even detecting it. Beijing's intention is obvious: to show that its most advanced aircraft can easily cross one of the most closely monitored chokepoints in Asia.

The geographical significance of this move is clear. The Korea Strait connects the East China Sea and the Sea of Japan, and is close to key U.S.-Japan bases that are crucial for any Taiwan Strait emergency. Some comments even claimed that the (J-20) "evaded THAAD," but this is just propaganda, not evidence. THAAD radar is optimized for ballistic missile defense, not for tracking stealth aircraft. Important to note is that China's stealth patrol in this corridor highlights the challenges faced by the integrated air and missile defense system of the U.S., Japan, and South Korea.

If the (J-20) can stealthily cross this corridor, they will be able to threaten some high-value assets with long-range air-to-air missiles such as the PL-15. Even if people believe that stealth fighters could pose a threat to allied early warning aircraft or refueling tankers, it would force them to loiter far from the battlefield, thus reducing surveillance coverage, shortening cruise time, and slowing response cycles. In a rapidly moving aerial campaign, this may mean the difference between timely interception and exploiting gaps.

The impact will be more profound. A successful, undetected overflight would weaken confidence in the credibility of the emerging U.S.-Japan-South Korea air and missile defense cooperation. Currently, this cooperation is limited in scale and heavily dependent on U.S. assistance, rather than a fully integrated network. If Tokyo and Seoul cannot demonstrate their capability to monitor one of the most closely watched chokepoints in the Northeast Asian region, Beijing may consider that stealth aircraft could more easily threaten key nodes at the onset of a conflict. This perception alone is sufficient to undermine deterrence, as it implies that China can freely blind the allies' sensors.

Finally, the undetected transit of the (J-20) fighter is critical to the operational layout of U.S. reinforcements. The Korea Strait is one of the few maritime routes connecting U.S. forces and its allies' naval forces from the East China Sea into the Sea of Japan. If Chinese stealth fighters can patrol this route without being detected, they can track, harass, or even target the actions of allied naval forces during their most vulnerable phase.

The result will bring dual risks: delayed U.S. arrival in South Korea, and insufficient air support, while Japanese and South Korean forces remain uncertain about the security of their back door. Once North Korea launches a full-scale invasion, Chinese stealth fighters could disrupt the movement of U.S. forces stationed in Japan toward the Korean Peninsula and threaten the Maritime Prepositioned Ships (MPS).

Countering Stealth: What Should Tokyo and Seoul Do

No fighter jet is truly stealthy. South Korea has invested heavily in developing anti-stealth radar, including the VHF radar from Hanwha Systems and a domestically developed long-range air defense radar, which recently completed and was widely reported to operate in the L-band. The Defense Development Agency also advanced the concept of passive radar using civilian broadcast signals. Combined with four E-737 "Peace Eye" early warning aircraft and potentially future E-7 early warning aircraft, Seoul has established an anti-stealth tripping system.

Japan has its dense radar network, Aegis destroyers, E-2D early warning aircraft, and new vessels equipped with SPY-7 Aegis systems. However, in the context of the Taiwan issue, Japan may shift its coverage to the east and south, leaving a gap in the north. Therefore, joint operations are essential.

Specific joint measures between Japan and South Korea should focus on five specific steps.

First, the two countries should establish a joint anti-stealth radar network in the Korea Strait, jointly deploying mobile VHF and L-band radars as well as passive sensors from Jeju Island and Ulleung Island to western Kyushu, connecting them into a single network to create a layered redundant detection grid that no single country could maintain alone.

Second, the two countries must move from information sharing to real-time joint flight path monitoring; the General Security of Information Memorandum of Agreement (GSOMIA) has opened the political door, but actual action requires establishing a joint flight path fusion group that reaches consensus on sensor reliability, automatic resolution of conflict data, and direct information provision to both countries' air defense authorities.

Third, Tokyo and Seoul should pre-design protected flight paths for early warning aircraft and refueling tankers north of the strait and defend them with sentinel fighters and deception tactics, preventing the (J-20) fighters from easily interfering with allied aerial reconnaissance.

Fourth, the two governments should expand infrared search and track systems on fighter jets and coastal tower stations, as infrared search and track systems are immune to electronic attacks and, when guided by passive radar, can provide additional means to track stealth aircraft in the challenging coastal environment of the strait.

Finally, Japan and South Korea should conduct joint exercises where radars are intentionally silenced, and tracking is maintained only by passive and airborne sensors, practicing how to convert low-frequency radar signals into weapon-grade tracking signals within minutes.

To achieve this goal, Washington, Tokyo, and Seoul must continue efforts based on the 2023 Camp David Summit, as trilateral security cooperation is crucial.

High Stakes

China's state media has never explicitly mentioned the exact time of the (J-20) fighter's patrol, and the allied sensors may have detected this overflight, but have not publicly disclosed it. However, Beijing showcased this move before the anniversary of the founding of the People's Liberation Army and amid escalating Sino-Japanese tensions, indicating its intention to normalize stealth patrols, allowing them to cross this strategic location. This is more about shaping perception than achieving tactical effects: showing that even the most closely monitored corridors can be breached.

Sources: Geopolitics

Time: August 27

Author: Kim Joo-hyung

Dr. Kim Joo-hyung currently serves as the Director of the Institute for Security Management, a defense think tank affiliated with the National Assembly of South Korea.

"Linguistic Study | Translation"

Original: www.toutiao.com/article/1841773013830663/

Statement: This article represents the views of the author.