On June 7, the Japan Maritime Self-Defense Force (JMSDF) and the Republic of Korea Navy (ROKN) conducted a search and rescue exercise (SAREX) west of Japan’s Goto Islands, marking the first such drill between the two navies after a nine-year hiatus.

The exercise involved the Kongo-class Aegis destroyer JS Kongo (DDG-173) and an SH-60K helicopter on the Japanese side, while the ROK Navy deployed ROKS Cheon Ja Bong (LST-689), a Cheon Wang Bong-class tank landing ship. In addition to search and rescue operations, the drill included a link exercise (LINKEX) for tactical data sharing between ships and aircraft, cross-deck helicopter operations, and a photo exercise (PHOTOEX) — elements that build the kind of interoperability applicable well beyond humanitarian missions. 

The JMSDF said the exercise improved search and rescue capabilities and strengthened cooperation between the two sides.

The resumption carries considerable symbolic weight. Bilateral defense ties collapsed after a South Korean destroyer allegedly locked its fire-control radar onto a JMSDF P-1 maritime patrol aircraft in December 2018, triggering one of the worst crises in postwar Japan-South Korea defense relations. Exchanges were effectively frozen for years.

A turning point came at the 2024 Shangri-La Dialogue, when the two defense ministers agreed on measures to prevent a recurrence. The January 2026 Yokosuka ministerial meeting then formalized the resumption of SAREX alongside agreements to hold annual defense ministerial meetings and explore cooperation in artificial intelligence, unmanned systems, and space.

Japanese Defense Minister Koizumi Shinjiro described the exercise as “the beginning of a new chapter” in bilateral defense cooperation and is expected to visit Seoul later this month for further talks.

The broader strategic backdrop is difficult to ignore.

North Korea’s advancing nuclear and missile capabilities remain the stated focus of bilateral security cooperation. But China’s expanding naval presence across the East China Sea, South China Sea, and waters around Taiwan, combined with growing uncertainty over future U.S. alliance commitments, has created additional incentives for Tokyo and Seoul to deepen coordination.

Neither government names China in official documents — the January 2026 joint statement refers only to “the increasingly severe security environment” — but the structural pressures are evident. As Japanese Prime Minister Takaichi Sanae and South Korean President Lee Jae-myung moved to stabilize bilateral relations in May, uncertainty over Washington’s future regional role provided an additional incentive for closer coordination.

Yet the same week that SAREX made headlines, Lee offered a strikingly candid reminder of how far the relationship still has to travel.

Speaking at a press conference marking his first year in office on June 8, Lee acknowledged that an Acquisition and Cross-Servicing Agreement (ACSA) — which would allow the JSDF and ROK military to exchange fuel, food, and supplies — has “practical necessity.” But he added that it is “currently difficult for the public to accept this emotionally,” citing the legacy of Japanese colonial rule.

“We were beaten in the past,” he said. “People feel — even if we need to get along now, can we really fully cooperate?”

The frankness is worth noting.

ACSA is, in operational terms, a modest administrative arrangement — essentially a reimbursement mechanism for logistics support. Japan signed a similar agreement with Australia in 2010 without significant controversy. But in the South Korean political context, it is fraught with historical symbolism, functioning as a proxy debate about the limits of Japan-ROK military integration.

Experts at a recent public seminar held at Keio University in Tokyo noted the gap. One Japanese analyst described ACSA as “no more than a billing procedure,” while a Korean researcher called it “a politicized agenda,” arguing that once the issue became politicized, concluding the agreement grew increasingly difficult regardless of its practical merits.

This gap between strategic logic and domestic political constraint defines the central tension in Japan-ROK defense relations today.

The security case for closer cooperation is stronger than it has been in decades. North Korea’s nuclear and missile capabilities continue to advance, while Pyongyang’s growing military partnership with Russia and China’s renewed efforts to strengthen ties with North Korea have added a new layer of complexity to Northeast Asia’s security environment.

Japan has overhauled its defense posture, eased restrictions on arms transfers, and is actively seeking security partners. South Korea, meanwhile, has built one of Asia’s most capable defense industries. The complementarities are real.

And yet history does not simply yield to strategic calculation. Lee’s comments suggest a leader who understands the security rationale but cannot move faster than his political base allows.

The resumption of SAREX illustrates how far bilateral defense cooperation has recovered since 2018. The continuing controversy surrounding ACSA demonstrates that normalization is not the same as strategic integration.

Whether the relationship can eventually advance from symbolic normalization to substantive strategic cooperation will depend not only on the regional security environment, but on the ability of political leaders in both countries to manage the enduring weight of history. For now, the return of SAREX demonstrates that practical cooperation is moving ahead, even if political reconciliation remains incomplete.