S. Korea-Japan defense ties deepen, but ACSA gap persists amid Black Eagles visit

South Korea and Japan announced plans to expand defense cooperation in air force, naval and advanced technology at their bilateral defense ministers' meeting, even as Japan's repeated push for an Acquisition and Cross-Servicing Agreement drew a noticeably cool response from Seoul.

Defense Minister Ahn Gyu-baek and Japanese Defense Minister Junichiro Koizumi met Sunday at the Ministry of National Defense in Yongsan, Seoul, agreeing to strengthen cooperation in aerobatic team exchanges — between South Korea's Black Eagles and Japan's Blue Impulse — naval search-and-rescue exercises (SAREX), and advanced technology including AI. The two ministers said they would "develop future-oriented defense cooperation through mutual understanding and trust."

The aerobatic team exchange commitment builds on a milestone from Jan. 28, when the Black Eagles made their first-ever stopover at Japan Air Self-Defense Force's Naha base in Okinawa Prefecture for mid-flight refueling, during which pilots from both teams met. The agreement signals that such exchanges will continue rather than remain a one-time event. The ministry noted, however, that no decision has been made to regularize Black Eagles stopovers and refueling support at Japanese bases.

Koizumi arrived Saturday, the day before the talks, and visited the Black Eagles unit at Wonju Air Base in Gangwon Province — the first foreign defense minister to do so. Japan's Defense Ministry posted about the visit on X, noting that the aerobatic team had stopped over in Okinawa in January.

That reference is widely seen as a deliberate move to highlight the case for a bilateral logistics support agreement with South Korea. While ACSA was not on the official agenda, Japan raised the need for such a pact during the talks, citing the security environment on the Korean Peninsula and in the broader region.

ACSA allows the mutual provision of military supplies — including ammunition, fuel and food — in contingency situations. Japan has concluded such agreements with the United States, Australia, the United Kingdom and India, among others, and the framework is regarded as a quasi-alliance-level support arrangement directly tied to sustained operational capability.

Japan raised the same demand at a bilateral meeting on the sidelines of the Shangri-La Dialogue in Singapore in May. Analysts say Tokyo's repeated push for ACSA reflects its broader aim of institutionalizing trilateral South Korea-US-Japan security cooperation to strengthen regional response capabilities.

Seoul, however, has held firm, maintaining that it is "not reviewing" the agreement out of consideration for historical grievances and public sentiment. A ministry official said the government "is not currently reviewing the conclusion of an ACSA," adding that it was "limited in disclosing specific details of defense diplomacy consultations."

The ACSA debate goes beyond a simple logistics arrangement — it cuts to the question of how far South Korea is willing to integrate militarily within the framework of bilateral and trilateral cooperation with Japan and the United States. The meeting reaffirmed a dual dynamic in which the two sides broaden practical cooperation while drawing a clear line at ACSA, widely seen as the ceiling of military ties. With Japan pressing for institutionalization and South Korea opting for a gradual approach, analysts expect the ACSA question to resurface repeatedly.