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It’s time to rethink Japan’s missile defenses

The government of Japan’s recent decision to suspend work on its Aegis Ashore installation has raised concerns about the U.S.-Japan alliance and generated protests from missile defense advocates. Critics of the decision argue the system is needed to protect Japan from a North Korean ballistic missile attack and can do so more efficiently than today’s approach of using a flotilla of Aegis destroyers rotationally deploying to the Sea of Japan.

The critics are partly right, as the program’s cost doubled from the government’s original optimistic estimates. However, at about $1.8 billion each, the two planned Aegis Ashore facilities are less expensive than the three or four $1.6 billion Aegis destroyers they partially replace.

But Japan’s decision shows cost isn’t the only — or even the most important — consideration in protecting Japan from a missile attack. The Abe government should use this pause to transform its missile defense approach to better address growing threats from China and North Korea.

Japan’s defense minister cited cost as one reason for the suspension, but a more significant stumbling block is worry from communities around the Aegis Ashore sites that missile debris could fall on their homes and that high-power radars could harm nearby inhabitants. Although these concerns may be unfounded, they suggest Japan’s Ministry of Defense should move to a distributed missile defense architecture that relies less on self-contained Aegis Ashore sites and destroyers.

The Japanese MoD is exploring alternatives to Aegis Ashore, including putting the whole installation on a floating barge or expanding today’s all-destroyer missile defense architecture. These approaches would address community concerns but would likely be more expensive than the current approach and would not necessarily improve the defense of Japan.

One of the fundamental challenges with Aegis Ashore is capacity. Even with the new SPY-7 solid-state radar, Aegis Ashore will be susceptible to the decoys and other penetration aids being fielded by North Korea and China that could cause SM-3 interceptors to miss their targets.

Moreover, both countries could overwhelm the 24 SM-3s in the Aegis Ashore magazine with large salvos of conventional and nuclear missiles, especially if defenders shoot multiple interceptors at each incoming missile.

Japan could help address its potential capacity challenges in part by attacking ballistic missiles during the boost phase, when they are easier to attack and require fewer interceptors. Aircraft with air-to-air missiles could engage ballistic missiles shortly after launch from airspace near enemy territory. This may not be feasible around China, but would be possible over North Korea.

Unmanned medium-altitude, long-endurance aircraft like the MQ-9 Reaper would enable Japanese forces to affordably conduct boost-phase intercepts at acceptable risk. These aircraft would use infrared sensors to cue engagements, which could also solve a key capability gap for the Japanese MoD by providing early warning to Japanese forces at home.

Countering missiles that evade boost-phase defenses will require a combination of mid-flight engagements at high altitudes using expensive SM-3 interceptors; lower-altitude midcourse engagements with Terminal High Altitude Area Defense interceptors; and short-range defenses using Patriot Advanced Capability-3 interceptors.

Japan currently fields all these surface-to-air missiles, but their use is not coordinated to maximize the air defense network’s efficiency.

In a more distributed missile defense architecture, SM-3s would be deployed exclusively on Aegis destroyers, which could carry more interceptors in their 96-cell vertical launch system magazines compared to Aegis Ashore. To enable the destroyers more flexible operating areas, Japan could retain the radar of Aegis Ashore and use the Cooperative Engagement Capability datal ink to share targeting information between radars and ships. This approach would address community concerns about missile debris. And to reduce worries over harm from radio frequency emissions, the radars could be relocated to less populated areas or placed on barges.

To avoid using SM-3s against every incoming ballistic missile, some of which could be decoys, Japanese forces need command-and-control systems that can match incoming weapons with the interceptor that can destroy them at the lowest cost and least impact on remaining defensive capacity. For example, missiles targeted at locations protected by PAC-3 or THAAD could be more efficiently engaged by those systems compared to SM-3s.

Missile defense command-and-control systems are available. The Aegis Combat System does this today for individual ships, and the U.S. Army’s Integrated Air and Missile Defense Battle Command System is intended to coordinate missile defenses for ground forces. A command-and-control system like these will be essential if Japan is to establish sufficient air defense capacity to defeat a North Korean attack, much less an assault from China.

Japan needs to implement a new missile defense architecture that can affordably address the size and capability of the threats it faces today. The path it was on — using SM-3s to engage almost every missile, and relying on THAAD and PAC-3 interceptors to catch the leakers — is not only inefficient; it also ensures large areas of Japan will be undefended against all but the smallest salvos. The Japanese MoD should exploit new systems for boost-phase intercept as well as command and control to better protect its territory and people.

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