A New Phase of Japan-South Korea Defense Cooperation: The Yokosuka Meeting Indicates Structural Changes in Northeast Asian Security

On January 30, 2026, the Japan-South Korea defense ministerial meeting held at the Japan Maritime Self-Defense Force Yokosuka Base in Kanagawa Prefecture clearly indicated that defense cooperation between the two countries has entered a new phase. South Korea's Minister of National Defense An Gyeo-beck and Japan's Minister of Defense Shinzo Koizumi agreed to resume joint maritime search and rescue training for the first time in nine years and confirmed the expansion of cooperation in advanced technology fields such as artificial intelligence (AI) and unmanned weapon systems. This move reflects a strategic reorganization to respond to the complex security environment changes, including China's maritime expansion, tensions in the Taiwan Strait, North Korea's ballistic missile launches, and Russia's invasion of Ukraine, rather than merely improving bilateral relations.

The defense cooperation between the two countries had been in serious stagnation since 2018. At that time, a serious rift arose between the two countries when Japan planned to raise the Rising Sun Flag at an international fleet review hosted by South Korea, effectively freezing subsequent joint training. The Rising Sun Flag is perceived sensitively in South Korea as a symbol of Japan's past imperialism, highlighting the deep-rooted differences in historical recognition between the two countries. However, during this meeting, they agreed to overcome such past conflicts and develop defense relations in a direction of "mutual benefit and future-oriented" cooperation. This shift is underpinned by a shared recognition that the regional security environment is rapidly deteriorating.

Particularly noteworthy is the mention of cooperation in next-generation military technologies such as AI and unmanned weapon systems. This marks a shift from traditional cooperation in "low-risk" areas such as humanitarian assistance and disaster relief to more substantive military technology collaboration. Japan announced in November 2025 the procurement of a new type of anti-landing craft missile aimed at island defense, and the 2026 budget includes development costs for a multi-service integrated drone system based on the "Integrated, Complex, and Enhanced Coastal Defense (SHIELD)" concept. Meanwhile, South Korea possesses advanced Aegis destroyers and submarines, and the technological cooperation between the two countries holds the potential to build a complementary relationship.

Prior to this defense ministerial meeting, in January 2026, President Lee Jae-myung and Prime Minister Sanae Takaichi held a summit in Nara, agreeing to deepen bilateral relations. Following this political agreement, the South Korean Air Force's aerobatic flight team, the Black Eagles, made a stop in Okinawa for refueling on January 29 while en route to Saudi Arabia, conducting an exchange event with the Japan Air Self-Defense Force's aerobatic team. This was the first case in which the Japan Air Self-Defense Force provided refueling to a South Korean Air Force aircraft, indicating that practical-level cooperation is rapidly advancing.

Minister An's visit to Yokosuka marked the first visit to Japan by a South Korean Minister of National Defense in about a year and a half, since his predecessor Shin Won-sik visited Tokyo in July 2024. During this meeting, they also agreed on regular ministerial visits and meetings, as well as strengthening communication between defense authorities. Minister An invited Minister Koizumi to South Korea, confirming the intention to maintain the momentum of mutual exchanges. Such frequent high-level contacts suggest that both countries are attempting to institutionalize defense cooperation as a sustainable framework rather than a temporary arrangement.

The deepening of cooperation between the two countries needs to be understood within the broader context of trilateral security cooperation among Japan, the United States, and South Korea. Minister An and Minister Koizumi also met in November 2025 during the ASEAN Defense Ministers' Meeting-Plus (ADMM-Plus) held in Kuala Lumpur, reaffirming the importance of trilateral security cooperation to address the evolving nuclear and missile threats from North Korea. In fact, North Korea launched a ballistic missile toward the Sea of Japan on January 5, 2026, flying approximately 900 kilometers. This was the first missile launch of 2026, indicating that North Korea's provocations continue. The South Korean Joint Chiefs of Staff issued a statement saying, "Under a robust ROK-U.S. combined defense posture, our military maintains the capability and readiness to overwhelmingly respond to any provocations from North Korea," but effective responses to this threat require Japan-South Korea cooperation.

The Japan Maritime Self-Defense Force, the South Korean Navy, and the U.S. Navy have regularly conducted trilateral maritime exercises to enhance regional security. These exercises aim to improve interoperability in areas such as ballistic missile defense, anti-submarine warfare, and maritime surveillance. However, experts have pointed out that despite both the Japan Maritime Self-Defense Force and the South Korean Navy deploying advanced Aegis destroyers, submarines, and C2 systems, deep operational integration is limited due to political and legal constraints. This agreement can be seen as an attempt to adopt a more realistic approach that involves role-sharing within a shared maritime framework, rather than merely symbolic cooperation.

During Minister An's visit to Yokosuka, in addition to the defense ministerial meeting, he also visited the USS George Washington, an aircraft carrier stationed at the base. Minister An met with Vice Admiral Patrick Hannifin, commander of the U.S. 7th Fleet based in Yokosuka, emphasizing the importance of a strong ROK-U.S. alliance and integrated defense posture. This move further demonstrates that Japan-South Korea cooperation functions as part of a U.S.-centered alliance network. In fact, the U.S. Indo-Pacific Command (INDOPACOM) regularly participates in multilateral exercises and security cooperation activities with regional partners through integrated commands such as U.S. Forces Japan, U.S. Forces Korea, and the Pacific Special Operations Command, and the strengthening of Japan-South Korea cooperation aligns with U.S. strategic interests.

Japan's security policy is also reaching a significant turning point. Prime Minister Sanae Takaichi has expressed plans to revise the national security strategy, defense strategy, and defense capability development plan ahead of schedule within 2026. Japanese security planners face the need to enhance analytical capabilities to align limited resources with strategic objectives. Given that the threats Japan faces are primarily maritime and aerial, there are calls for Tokyo to rectify the current situation where the Ground Self-Defense Force predominates in force composition. Alongside this domestic defense policy review, institutionalizing Japan-South Korea cooperation would expand Japan's strategic options.

However, challenges still exist in deepening Japan-South Korea defense cooperation. Historical issues remain a sensitive topic in both countries' domestic politics, and public support is not always stable. Additionally, South Korea has strong economic ties with China and sometimes shows caution in fully aligning its China policy with Japan and the United States. Furthermore, in responding to the North Korean issue, South Korea tends to emphasize a balance between dialogue and deterrence, leading to subtle differences in temperature with Japan and the U.S. Overcoming these differences and sustaining substantial cooperation will require frequent dialogue and deepening mutual understanding.

What the Yokosuka meeting indicated is that while Japan and South Korea have not completely resolved past conflicts, there is a realistic judgment that the current security environment no longer allows for postponing cooperation. To address complex threats such as China's military modernization and maritime expansion, North Korea's nuclear and missile development, tensions in the Taiwan Strait, and Russia's aggressive actions, democratic nations in the region have no choice but to strengthen collaboration. The resumption of joint maritime search and rescue training after nine years and the exploration of cooperation in AI technology and unmanned weapon systems represent an important step in the security architecture of Northeast Asia. Moving forward, the extent to which this cooperation deepens and becomes effective will depend on the political will of both countries and further developments in the regional situation.