Japan, South Korea, U.S. unite against North Korean missile threats

Felix Kim

Enhanced defense communication among Japan, South Korea and the United States, including real-time sharing of missile defense data, promises to boost deterrence against North Korean missile threats. When combined with trilateral defense exercises, it also will send a strong message to Pyongyang and Beijing to refrain from seeking to disrupt the regional status quo by force, experts say.

The U.S. has longtime treaty alliances with Japan and South Korea. In a statement following their mid-August 2023 summit in the U.S., Japanese Prime Minister Fumio Kishida, South Korean President Yoon Suk Yeol and U.S. President Joe Biden agreed to operationalize real-time sharing of missile warning data on North Korea. Moreover, they resolved to hold trilateral multidomain military exercises to enhance capabilities and coordination.

The message to Pyongyang and Beijing is clear, according to Dr. Jeffrey Hornung, a defense analyst with the Rand Corp.

“Their nightmare scenario is happening right now because Japan, ROK [Republic of Korea] and the U.S. are on the same page,” Hornung told FORUM. “If I was a Chinese defense planner, and definitely if I was a North Korean planner, I’d be looking a little differently at my plans now, realizing that, OK, we’re not facing three separate militaries anymore. There is the potential that there’s going to be more coordination here.”

In 2016, Tokyo and Seoul signed the General Security of Military Information Agreement on the bilateral exchange of information. In June 2022, the nations expressed hope for further implementation of the treaty to counter North Korean missile threats.

“South Korea has an enormous array of land sensors,” Hornung said. “And so, they’re going to arguably have the quickest knowledge that something is being launched.”

By triangulating South Korean data with that gathered by Japanese and U.S. satellites, the nations will enhance their ability to detect and analyze a missile’s trajectory and threat level and, if necessary, shoot it down.

Trilateral data sharing and defense coordination also could bolster reconnaissance.

“I do think that that’s where the operational part matters in that they could help each other, whether it’s missile launches, whether it’s unidentified ships or trying to get a sense of just [North] Korean technology,” Hornung said. “Is it, for instance, a launch just from a terrestrial launcher or is it coming from submarines as well, and how far out are these subs?”

Additional trilateral defense exercises will build on the gains from the partners’ maritime ballistic missile defense warning test in mid-August 2023, he said. Adapting current exercise models that simulate a missile attack to further demonstrate data-sharing capabilities and improve interoperability among the three militaries “would be critical.”

Felix Kim is a FORUM correspondent based in Seoul, South Korea.