TOKYO -- Japan's decision to halt the deployment of the U.S.-made Aegis Ashore missile defense system will weaken the nation's ability to counter the North Korean threat and could also strain the security partnership with Washington, its most important ally.
The move upends Japan's plan to add another layer to the current two-shield protection against North Korean missiles that relies on Aegis-equipped destroyers and Patriot PAC 3 surface-to-air missile system. As Japan gets ready to renegotiate the costs of hosting U.S. bases, it could also face added pressure from Washington, which is demanding Tokyo increase its share of the burden.
Tokyo had decided in 2017 to procure two of the land-based batteries from the U.S. for an initial price tag of $2.1 billion to bolster its defenses in response to North Korea's continued nuclear and missile development. But the costs have since snowballed, and Defense Minister Taro Kono said Monday that it is "not logical" to stick to the original plan given the soaring cost and time needed.
Yet "the threat from North Korea has not disappeared -- on the contrary, its technology has grown more advanced," said Katsutoshi Kawano, who served as chief of the Self-Defense Forces' Joint Staff when the deployment decision was made.
"Right now, I don't see any system that can replace Aegis Ashore," he said.
Japan will have to go back to relying on Aegis-equipped vessels, according to Kono. But former Defense Minister Itsunori Onodera argued if Aegis-equipped vessels respond to North Korea, defenses for Okinawa and its surrounding islands in Japan's southwest will suffer.
And depending on the two-layer setup "won't allow us to ease the burden on the short-handed Maritime Self-Defense Force," which was part of the reason behind the Aegis Ashore deployment, Kawano said.
Japan's defense must operate "without gaps for 24 hours a day, 365 days a year," former Defense Minister Shigeru Ishiba said Tuesday.
The suspension risks causing friction between Japan and the U.S. A 2018 report by the Washington-based Center for Strategic and International Studies suggested that Japanese Aegis Ashore sites could be used to protect "critical areas" including Hawaii and Guam from ballistic missiles and other threats.
The sites chosen for the batteries, in Akita and Yamaguchi prefectures, lie along the paths that North Korean missiles bound for Hawaii or Guam would likely follow. In 2019, then-Defense Minister Takeshi Iwaya said Japan could shoot down such missiles under its "limited right to collective self-defense."
"I don't see how [the Aegis Ashore suspension] has a positive effect on the alliance," said Jeffrey Hornung, a political scientist at the American think tank Rand Corp.
Heigo Sato, a professor at Takushoku University, said the halt will have a "limited impact" on Washington's view of Japan and public opinion in the U.S. Given the lack of progress on the project in Japan so far, "hopes were not all that high" in Washington, he said.
The decision could affect the financial side of the bilateral relationship. Kono said necessary technical overhauls would cost 200 billion yen ($1.86 billion) and take a decade, but he did not discuss the potential cost of stopping the project.
Japan has entered Aegis Ashore-related deals totaling 178.7 billion yen and has already spent 12.5 billion yen. What will happen to these expenses remains unclear, with Kono saying only that Washington and Tokyo will discuss the matter.
Japan has used orders of expensive American military equipment, including 100 F-35 stealth fighters, to ease pressure from U.S. President Donald Trump to rebalance what he considers an unfair relationship by reducing its trade surplus and assuming more of the cost of hosting American troops.
The Aegis Ashore batteries -- the estimated cost of which has swelled to 450 billion yen ($4.2 billion) including operating expenses -- are a massive purchase. If Trump takes the halt to mean that the project is being scrapped, Washington may seek to make up for the loss by demanding more from Tokyo in this fall's negotiations over cost-sharing for American forces in Japan.
Similar talks between the U.S. and South Korea, following the expiration of their cost-sharing agreement at the start of the year, have hit a wall. Washington is seeking a $5 billion contribution from Seoul this year, five times the 2019 figure, and has refused South Korea's proposal of a 13% increase.
And a major source of the added time and cost -- refinements to ensure that booster rockets do not fall on nearby residential neighborhoods -- "were not a focus" originally, coming up only in discussions with local authorities, Kawano said. "Halting the project over boosters, when it's so important to figure out how to protect ourselves from nuclear and ballistic-missile threats, is difficult to understand."
Cooperation with the U.S. is central to national security in both Japan and South Korea. A rift with Washington could present an opportunity for not only North Korea, but also rival powers to the U.S.
"The suspension of the [Aegis Ashore] plan sends the wrong message to China and Russia," a senior Japanese Defense Ministry official said.