Japan, South Korea and the United States continue to deepen trilateral defense cooperation, with the three countries agreeing Sunday to start sharing real-time missile-warning data next month to better detect and assess North Korea’s increasingly frequent ballistic missile launches.
Following talks between the countries' defense chiefs, the three sides said the data-sharing mechanism is now "in the final stages of testing" and would be "fully operationalized by the end of December," according to a Pentagon statement.
The meeting took place during U.S. Defense Secretary Lloyd Austin’s visit to Seoul for annual bilateral security talks with his South Korean counterpart, Shin Won-sik, with Defense Minister Minoru Kihara joining the meeting via video link.
Noting that the trilateral defense partnership is now “stronger than ever,” the top officials also agreed to formulate a multiyear joint training plan before the end of the year to conduct trilateral exercises “more systematically and efficiently.”
Meanwhile, bilateral talks Monday between Austin and Shin also yielded results, as the two allies announced a revision of their "tailored deterrence strategy" on North Korea for the first time since its adoption in 2013.
The document is classified, but is believed to have been updated to reflect changes in the allies’ strategy to counter Pyongyang’s increasingly advanced nuclear and missile capabilities.
This comes as Washington deploys more strategic assets to the region while integrating Seoul into its planning for nuclear contingencies on the Korean Peninsula via the recently established Nuclear Consultative Group.
Tokyo, Seoul and Washington have been rapidly expanding defense cooperation amid common security threats, particularly Pyongyang's unprecedented spate of ballistic missile launches and other weapons tests in recent years.
In late October, the three countries held their first-ever trilateral aerial exercise. This was followed in early November by an agreement to launch high-level consultations on how to counter North Korean cyberactivities.
While Pyongyang has traditionally sought to drive wedges between the three countries, its belligerent rhetoric and repeated weapons tests have instead pushed Seoul and Tokyo closer, making both sides more willing to put aside their long-standing political differences and focus on mutual security interests.
Underpinning the rapprochement is a trilateral pact reached at August’s Camp David summit that laid the foundation for future defense initiatives.
Relations between Japan and South Korea have had their peaks and valleys, including periods of progress that have been swiftly reversed after changes in the countries’ security or political environment.
But to reduce the risk of another reversal, Washington, Seoul and Tokyo are now trying to institutionalize three-way defense cooperation.
“Without such a foundation, discussions of cooperation would return to zero whenever there is a change of administration, or a political swing in each country,” said Masashi Murano, a Japan defense expert at the U.S.-based Hudson Institute.
Missile defense cooperation, particularly the sharing of missile-warning data, was one of the key elements of the Camp David agreements.
As part of this plan, which dates back to the countries’ joint Phnom Penh statement in November 2022, the partners are independently linking their radars to a common platform at the U.S. military’s Indo-Pacific Command headquarters in Hawaii.
In the past, Japan and South Korea have shared missile information via the United States as their trusted intermediary. However, the practical benefit of directly sharing information in real-time is that “more data from different locations will boost the three nations’ ability to monitor missile launches,” said Naoko Aoki, an associate political scientist at the Rand Corp.
The integration of South Korean and Japanese sensor capabilities will allow them to better understand what is going on and deal with the situation more quickly, she added.
The idea is to make the most of the countries’ combined resources to develop a true trilateral common operating picture.
“It will make their missile defense missions more efficient and effective,” said James Schoff, senior director of the U.S.-Japan NEXT Alliance Initiative at the Sasakawa Peace Foundation USA, noting that the partners will be able to identify North Korean missiles “from various angles and earlier in flight, thus increasing missile defense accuracy.”
This is particularly important in any attempts to intercept North Korea’s latest, more maneuverable missiles.
Japan has had difficulties in responding to North Korean missile launches due to the limitation of its radar coverage.
“While terrestrial radars deployed across Japan and on Aegis destroyers in the Sea of Japan are highly capable, they cannot detect targets over the horizon, meaning that accurate tracking requires waiting for the missile to ascend,” said Murano.
In contrast, radars and other surveillance assets deployed in South Korea — and thus much closer to the launch sites — can detect missiles immediately after launch — or even pre-launch indications — he said.
The countries’ growing defense cooperation is not only meant to prepare for worst-case scenarios but also to have a deterrent effect on Pyongyang and make it think twice before firing missiles at any of the three countries.
At the same time, it is designed to show that trilateral cooperation has “staying power and real substance” while warning North Korea and other states in the region about the potential integration of Washington’s alliances with Tokyo and Seoul, said Christopher Hughes, a Japan expert and professor at Warwick University in Britain.
That warning may also be aimed at Beijing, which has long suspected that South Korea’s deployment of the U.S. THAAD ballistic missile defense system is also aimed at China.
“The addition of Japanese sensors, and maybe eventually interceptors, as part of a U.S.-led extended deterrence system may make China only more sensitive to this challenge,” said Hughes, adding that the three countries may also seek to step up intelligence-sharing and missile defense efforts down the line.
Such a level of trilateral cooperation, he added, would also be important for Japan’s potential use of so-called counterstrike capabilities against North Korean bases and command-and-control nodes in case of a conflict.
“Japan’s acquisition of long-range weapons to hit back at North Korean missile capabilities means that it could become a direct combatant on the Korean Peninsula for the first time since the end of World War II,” Hugues said.
However, the use of such weapons would need to be coordinated closely with not only the United States but also South Korea to avoid any undue escalation of tensions or duplication of military efforts, he added.
Experts agree that a long road ahead remains for the normalization of Japan-South Korea defense ties.
However, trilateral momentum is building rapidly to routinize cooperation and send a strong message of deterrence.
“Trilateral cooperation is essential as the North Korean nuclear and missile threat continues to grow,” Murano said, adding that once this defense foundation is established, “it will be difficult to break.”
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