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Limitations to missile interception exposed in latest N. Korean missile launch

Prime Minister Shinzo Abe, left, is seen at a National Security Council meeting at the prime minister's office in Chiyoda Ward, Tokyo, on Aug. 29, 2017. (Photo taken from the prime minister's office Facebook page)

Speculation that the North Korean missile that flew over Japan on the morning of Aug. 29 was an intermediate-range ballistic missile (IRBM) has become more common as authorities investigate the incident. The missile followed its standard flight path, falling into the Pacific Ocean after passing over Japan, hinting that North Korea is getting closer to full-fledged deployment of its missile systems.

But if North Korea continues to launch missiles without giving away that it is about to do so and develops multiple-warhead missiles, responding to missile launches with interceptor missiles will become increasingly difficult.

Because North Korea had threatened to launch missiles toward the sea around the U.S. territory of Guam, the Japanese government had deployed Patriot Advanced Capability-3 surface-to-air systems (PAC-3) to four prefectures in the Chugoku and Shikoku regions.

But the missile that was launched by North Korea on Aug. 29 passed over Japan's northernmost island of Hokkaido, in a completely different area from where the PAC-3 systems had been set up. The incident exposed the limitations to what Japan can do, as the entire archipelago cannot be protected with the limited number of missile defense systems it has.

"We were not given any advance notice that this would happen, and the missile flew over Japan without authorization," Chief Cabinet Secretary Yoshihide Suga said at a press conference on Aug. 29, expressing a keen sense of crisis. "The seriousness of the latest missile launch is extremely grave in a way that is different than usual."

The missile, without prior notice, flew over Japan and fell into the Pacific Ocean. There's no denying that the incident may be just one in a series, and will continue to put the Japanese public ill at ease. Because of this, the Japanese government appeared to be more tense than usual.

The missile defense system of Japan's Self-Defense Forces (SDF) comprises a two-tier system: the ship-based Standard Missile-3 (SM-3) mounted on four Aegis vessels, which intercept missiles whose engines have burned out and are passing through beyond the Earth's atmosphere, and the PAC-3 system, which intercept warheads that were somehow not destroyed by the SM-3 at an altitude of about a dozen or so kilometers.

The Japanese government has responded to North Korea's multiple ballistic missile launches by issuing a standing order for the SDF to shoot down any missiles that come flying toward Japan. In response to reports that North Korea was threatening to launch missiles in the direction of Guam, the government deployed PAC-3 systems to Ground SDF garrisons in Shimane, Hiroshima, Ehime and Kochi. It also dispatched SM-3-equipped Aegis vessels to the Sea of Japan.

However, some questioned the efficacy of such actions taken by the Japanese government, seeing them more as a political statement that it was prepared to guarantee the public's safety than as actual measures to destroy missiles.

Under the Self-Defense Forces Act, the only missiles that the SDF is permitted to intercept are those that are at risk of landing on Japan, or are in danger of causing harm to human life and assets in Japanese airspace and territorial waters -- with the exception of cases in which Japan is involved in a military contingency.

If missiles launched toward Guam were to be flying on a standard flight path, the SDF had planned not to intercept them, except in cases in which a mishap resulted in the missile falling onto Japanese territory. But missiles that are functioning irregularly are highly unlikely to fly on a standard trajectory, which would make it virtually impossible to predict where they would fall.

Japan is currently in possession of just 34 PAC-3 systems, and to deploy them nationwide would be incredibly difficult, in terms of both cost and personnel. The government is planning to introduce the land-based Aegis Ashore system equipped with the SM-3, but that alone does not guarantee successful missile interception.

North Korea is improving technology relating to transporter erector launchers, a mobile missile carrier that can transport and fire missiles, and the simultaneous launch of multiple missiles, making missile interception increasingly more difficult.

A PAC-3 missile interceptor is seen during a drill conducted at the U.S. Yokota Air Base in Fussa, Tokyo, on Aug. 29, 2017, after North Korea launched a missile that flew over Hokkaido before plunging into the Pacific Ocean. (Mainichi)

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