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Sam Beltran

Japan and South Korea’s prominent roles in this year’s US-led Rim of the Pacific (Rimpac) military exercises have fuelled speculation over whether the two neighbours might set aside their historical grievances and deepen defence cooperation.
Held in waters off Hawaii, this year’s Rimpac is the world’s largest maritime exercise, involving 30 nations, more than 30,000 troops and an armada of aircraft, surface ships and submarines.
Running from June 24 to July 31, the exercise saw South Korean Rear Admiral In-ho Kim serve as the commander of the combined forces maritime component, while Japanese Rear Admiral Takuo Kobayashi acted as vice-commander of the combined task force.
“For Rimpac 2026, what stood out is how quickly this multinational force integrated,” US Vice Admiral Jeffrey Jablon, commander of the combined task force, said at a virtual press briefing on Wednesday.
He added that a leadership structure that included Chile, South Korea, Canada and Japan in key command roles had allowed the force to operate as a “cohesive, capable team from day one”.
South Korea and Japan’s involvement in Rimpac comes even as the two US allies continue to disagree and occasionally clash over their difficult history from 1910 to 1945, when Tokyo colonised the Korean peninsula.

Nonetheless, William Chou, senior fellow and deputy director of the Japan chair at the Hudson Institute in Washington, said the senior Rimpac command positions held by top officers from both countries signalled that Tokyo and Seoul could move towards closer operational planning.
“This needs to be carried forward to other practical areas of military and naval cooperation as well,” Chou said.
Yuko Nakano, associate director of the US-Japan strategic leadership programme at the Centre for Strategic and International Studies in Washington, said former South Korean president Yoon Suk-yeol and ex-Japanese prime minister Fumio Kishida had laid the groundwork for closer cooperation, including at the trilateral 2023 Camp David summit during the Biden administration.
Despite subsequent leadership changes in the US, Japan and South Korea, engagement between Tokyo and Seoul had continued at the bilateral and trilateral levels, Nakano said.
Dongkeun Lee, a policy fellow at the Asia-Pacific Leadership Network, said the obstacles separating the two neighbours had begun to diminish since South Korean President Lee Jae Myung took office.
“Although some commentators expected the Lee administration to adopt a different approach to relations with Japan, it has instead demonstrated a pragmatic and constructive approach, reflecting the realities of the current geopolitical environment,” he added.
Maritime cooperation had become more urgent due to the increasingly complex situation in the East China Sea, the Taiwan Strait and the South China Sea, Lee said, noting that all were critical sea lanes for Japan and South Korea.

“Consequently, the two countries face the same geopolitical challenges, creating strong incentives for closer cooperation whenever opportunities arise.”
Kei Koga, an associate professor at Nanyang Technological University’s public policy and global affairs programme, said the exercises showed both countries were willing to “take greater initiative as regional security providers” instead of relying on the US for defence and security.
However, he said that Rimpac did not signal Tokyo and Seoul were poised to deepen defence cooperation to the point of “forming a military alliance or jointly planning for regional contingencies”.
Washington’s role
Sanghun Seok, a senior associate fellow at the Royal United Services Institute, said Washington’s role as a go-between would continue to be crucial even as Japan and South Korea explored closer cooperation.
He pointed to their different positions on the US-led Acquisition and Cross-Servicing Agreement, a bilateral military logistics pact covering the exchange of military support such as fuel, ammunition and equipment.
While Japan had been keen to explore the agreement with South Korea, Seoul responded cautiously, indicating that direct security cooperation between them remained politically sensitive, Seok said.
President Lee ruled out such a partnership in June, citing the need for Tokyo to resolve historical grievances first.

“US involvement makes bilateral security cooperation more acceptable to wary domestic audiences,” Seok said.
Chou said defence cooperation between Japan and South Korea would have to remain centred around the US “hub-and-spoke model”.
“While both countries recognise the importance of closer bilateral ties at a time when the US is demanding more from its allies, there remains much to do in terms of improving real cooperation” between Tokyo and Seoul, he added.
North Korean threat
Despite their differences, Japan and South Korea are likely to maintain a “minimum level” of defence cooperation due to the common threat they faced from North Korea, according to Koga.
Pyongyang is belligerent towards both countries and has carried out a series of missile tests near their territorial waters in recent years.

Although Tokyo and Seoul both took part in Rimpac, that cooperation was unlikely to extend to countering the North Korean threat, since the drills were designed to address “more sophisticated maritime threats”, Lee said.
Chou said that the security challenges posed by North Korea differed from other regional flashpoints.
“While Japan and South Korea are both concerned about North Korea, they will likely approach a Taiwan or a South China Sea contingency in different ways. The discrepancy between the two countries’ defence operational cooperation and diplomatic cooperation remains significant,” Chou said.
Satoru Nagao, a non-resident fellow of Hudson Institute, attributed the US’ continued engagement of Japan and South Korea to its desire to “share its security burden”, particularly in the case of North Korea.
“The US is especially worried about a two-front scenario. If the Korean War and the Taiwan crisis happened at the same time, the US and Japan would concentrate their forces to support Taiwan more. In this case, South Korea should take more charge with the support of the US and Japan. For such a nightmare scenario, US-Japan-South Korea cooperation is vital,” Nagao said.
Beijing sees Taiwan as part of China to be reunited by force if necessary. Most countries, including the US, do not recognise Taiwan as an independent state, but Washington is opposed to any attempt to take the self-governed island by force and is committed to supplying it with weapons.


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A team is seen at mission control console inside a South Korean maritime patrol aircraft during a joint exercise as part of the 2026 Rimpac exercise near Honolulu. Photo: The Korea Times

A South Korean Dosan Ahn Chang-ho-class submarine moored in Hawaii during the 2026 Rimpac exercise. Photo: The Korea Times

A Japanese soldier takes part in a joint exercise between the Japanese and the Peruvian navies at the 2024 Rimpac exercise in Waimanalo, Hawaii. Photo: Reuters

US marines take part in an evacuation operation during the 2026 Rimpac exercise in Hawaii on July 24. Photo: AFP

A rocket launcher fires a missile during a test overseen by North Korean leader Kim Jong-un in North Korea on June 25. Photo: KCNA/Reuters

Flight deck crew move a fuel tank onboard the USS Theodore Roosevelt as the aircraft carrier participates in the Rimpac exercise in waters south of the Hawaiian Islands on July 13. Photo: Reuters

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Command roles at Rimpac show Tokyo and Seoul can work together militarily, but history caps how far ties can go


Command roles at Rimpac show Tokyo and Seoul can work together militarily, but history caps how far ties can go.


US-led drills edge Japan and South Korea closer on defence

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Command roles at Rimpac show Tokyo and Seoul can work together militarily, but history caps how far ties can go

Command roles at Rimpac show Tokyo and Seoul can work together militarily, but history caps how far ties can go