A New Chapter in Japan-South Korea Defense Cooperation: The Strategic Significance of Resuming Joint Exercises After 9 Years and AI Collaboration

On January 30, 2026, Japan's Minister of Defense Shinjiro Koizumi and South Korea's Minister of National Defense Lee Jong-sup held talks in Seoul and reached a historic agreement to significantly strengthen defense cooperation between the two countries. This agreement includes a comprehensive framework for the resumption of maritime search and rescue (SAR) exercises that had been suspended since 2017, as well as the establishment of new cooperation frameworks in artificial intelligence (AI) and unmanned weapon systems. Amid the rapidly changing security environment in Northeast Asia, this move marks a crucial turning point for Japan and South Korea to overcome historical conflicts and step into substantial military cooperation.

According to a joint press statement from the defense authorities of both countries, Japan and South Korea agreed on the importance of steadily promoting defense cooperation and exchanges, and they agreed to hold mutual visits and talks between defense ministers annually. This formalizes the institutionalization of high-level dialogue that had stagnated since 2015. Notably, both countries have specified cooperation in "new domains." The joint research and development of unmanned combat systems utilizing AI technology goes beyond traditional military cooperation frameworks and demonstrates a defense cooperation model for the era of the Fourth Industrial Revolution.

The resumption of maritime search and rescue exercises holds strategic significance beyond merely reviving humanitarian cooperation. Since the incident on December 20, 2017, when a South Korean Navy destroyer illuminated a Japan Maritime Self-Defense Force P-1 patrol aircraft with fire control radar, maritime cooperation between Japan and South Korea has effectively been frozen. This nine-year gap has created a significant void in maritime security cooperation in the Sea of Japan and the East China Sea. However, with North Korea's ballistic missile launches becoming routine and the confirmation of a hypersonic missile launch toward the Sea of Japan on January 5, 2026, both countries have been compelled to re-recognize the necessity of practical cooperation.

The Japanese Ministry of Defense plans to deploy a new type of land-based anti-ship guided missile with a range of approximately 1,000 kilometers to the 5th Anti-Ship Missile Regiment of the Japan Ground Self-Defense Force in the 2026 fiscal budget. The deployment site, the Kumamoto Ken-gun garrison, is located in Kyushu facing the East China Sea and is seen as a positioning in anticipation of a contingency in the Taiwan Strait. At the same time, Japan is advancing the development of unmanned systems that involve multiple Self-Defense Forces under the "SHIELD (Synchronized, Hybrid, Integrated and Enhanced Littoral Defense)" concept. This is envisioned as a multi-layered defense against amphibious operations and demonstrates technological innovation in island defense.

On the other hand, South Korea is also showing rapid progress in the fields of unmanned systems and AI. The South Korean Army has begun the operational deployment of unmanned K-CEV combat engineering vehicles as part of its "TIGER Plus" modernization program. This system integrates AI weapon stations, drones, and explosive ordnance disposal robots, indicating that the South Korean military aims to build "advanced scientific and technological capabilities centered on AI-based unmanned combat systems." Japan's Mitsubishi Heavy Industries is also scheduled to conduct the first flight of an AI-driven unmanned aerial vehicle in November 2025, with plans to complete the research phase by March 2026.

The specification of cooperation in AI and unmanned weapon systems in this Japan-South Korea agreement indicates both countries' intention to jointly enhance capabilities while ensuring interoperability in these technological developments. This holds significant meaning within the framework of trilateral security cooperation among Japan, the United States, and South Korea. In November 2024, a joint exercise involving the U.S. Navy's George Washington Carrier Strike Group will be conducted, while the South Korean Navy simultaneously conducts combat experiments aimed at "building manned and unmanned integrated combat systems." It is expected that deepening cooperation in unmanned systems between Japan and South Korea will strengthen the technological foundation for operational collaboration among Japan, the U.S., and South Korea.

However, the progress in defense cooperation has provoked backlash from North Korea. On January 13, 2026, North Korean state media condemned Japan's launch of a new attack submarine, the mass production of new land-based anti-ship missiles, and recent defense enhancements as a "revival of past militarism." North Korea claims that these capabilities are intended for preemptive strikes and pose a significant risk to regional security. This indicates that North Korea is taking the strengthening of Japan-South Korea defense cooperation seriously in terms of its impact on the military balance on the Korean Peninsula.

China is also wary of the rapprochement between Japan and South Korea. Activities by the China Coast Guard and the People's Liberation Army Navy in the East China Sea and the Sea of Japan have been on the rise in recent years, and incursions into waters around the Senkaku Islands have continued into 2026. Japanese defense authorities recognize that China's maritime expansion, tensions in the Taiwan Strait and the South China Sea, Russia's invasion of Ukraine, and North Korea's ballistic missile launches are undermining the international order, with threats in cyberspace and outer space also increasing. In a New Year message for 2026, Chief of Staff of the Maritime Self-Defense Force Akira Saito emphasized that the role of the Maritime Self-Defense Force is becoming increasingly important in addressing these "complex security challenges."

The institutionalization of Japan-South Korea defense cooperation will have long-term implications for the regional security architecture. By institutionalizing annual defense minister meetings and strengthening communication between defense authorities, the risk of misunderstandings and accidental conflicts in the event of unforeseen circumstances can be reduced. Additionally, starting cooperation in humanitarian and non-combat areas, such as SAR exercises, makes it easier to gain public understanding and lays the groundwork for gradually expanding the scope of cooperation.

Furthermore, cooperation in cutting-edge technology fields such as AI and unmanned systems will create new opportunities for both countries' defense industries. The relaxation of Japan's three principles on defense equipment transfers, combined with South Korea's policy to expand defense industry exports, may open up possibilities for joint development and technology transfer in the future. This means that Japan and South Korea could deepen their economic and technological interdependence beyond mere military partnership, potentially contributing to the stabilization of their relationship.

The Japan-South Korea defense cooperation agreement of January 30, 2026, represents a significant turning point in the security environment of Northeast Asia. The resumption of joint exercises after nine years symbolizes overcoming past conflicts, while cooperation in AI and unmanned systems materializes a future-oriented strategic partnership. In the face of the triple challenges posed by North Korea's nuclear and missile threats, China's maritime expansion, and Russia's military provocations, the institutionalization of substantial defense cooperation between Japan and South Korea is an essential step for regional stability.