On Aug. 10, North Korea made an unprecedented announcement that it would develop a plan to test-fire four Hwasong-12 ballistic missiles on a path it said would cross Shimane, Hiroshima and Kochi prefectures, to land in the sea near the island of Guam.

The announcement of the detailed flight plan immediately raised a critical question in the minds of many Japanese: Would the nation’s anti-ballistic missile defense systems be able to intercept the North Korean missiles?

Experts seem divided over the capabilities of the ¥1.6 trillion defense systems.

Masahisa Sato, senior vice minister for foreign affairs, tweeted last week that it would be “difficult” to shoot them down if the Maritime Self-Defense Force’s Aegis destroyers, equipped with SM-3 anti-missile defense systems, were deployed in the Sea of Japan.

While others differ regarding technical capabilities, all experts agree that from a legal perspective the Self-Defense Forces would not be allowed to shoot down any missile flying toward Guam as described in Pyongyang’s announcement, despite recent moves to reinterpret the pacifist Constitution.

In 2014, Prime Minister Shinzo Abe declared that the long-standing interpretation of the Constitution had been changed, and argued that Japan can now make partial use of the right of collective self-defense to defend a key ally country — presumably the U.S.

But even under Abe’s controversial interpretation, Japan would not be allowed to attack a third country unless the nation’s “survival” was at stake and there were no other alternatives, experts pointed out.

“There would be no basis or meaning in shooting down such missiles. (The SDF) will monitor and shoot them down only if they would fall onto Japan’s territory,” said Retired Vice Adm. Yoji Koda, a former fleet commander with the Maritime Self-Defense Force, while speaking with The Japan Times.

Japan currently has a two layer ballistic missile defense structure that comprises four Aegis destroyers equipped with the SM-3 missile system and ground-based Patriot Advanced Capability 3 (PAC-3) batteries.

The PAC-3 missile system is designed to intercept a ballistic missile flying in its “terminal phase,” or the period shortly before it would reach a target on the ground. So any North Korean ballistic missile flying high over Japan on a route toward Guam would need to be intercepted using SM-3 missiles.

Koda maintained that Aegis destroyers deployed in the Sea of Japan are capable of intercepting North Korea’s Hwasong-12 ballistic missiles if they fly over the Japanese archipelago as Pyongyang’s announcement describes, given the estimated speed, altitude and distance.

But the U.S. military probably will deploy three of its own Aegis warship groups near both Japan and Guam. The U.S. also has the Terminal High Altitude Area Defense (THAAD) system on the western Pacific island, Koda pointed out.

“So the U.S. has a four-layer defense structure. The level of their readiness is much higher than that of Japan, so Japan wouldn’t need to help the U.S.,” Koda said.

Japan’s postwar Constitution had long been interpreted as strictly limiting the mission of the SDF to defend only the nation’s territory, banning the use of the right of collective self-defense as defined by the Charter of the United Nations. Under international law, a nation has the right to attack a third country assaulting an allied country even if the nation itself is not under attack.

But with the reinterpretation, Abe argues that despite the war-renouncing Article 9, Japan can partially use the right of collective self-defense if the nation’s “survival” is determined to be at stake.

More specifically, Japan would be allowed to use the right only if “people’s right to life, liberty, and the pursuit of happiness is fundamentally overturned,” according to Abe’s own interpretation. That wording originated from a previous government interpretation that was upheld for decades.

“We used that wording to refer to a situation where Japan is directly attacked by a foreign country” before Abe revised the constitutional interpretation, said lawyer Masahiro Sakata, who has served as chief of the Cabinet Legislation Bureau.

For this reason, Sakata has stated that the government would be allowed to use the right of collective self-defense only if such a potentially “catastrophic” contingency is feared.

But such a situation is “unimaginable” if the North shoots ballistic missiles into the sea near Guam, even if some U.S. bases there are partially destroyed, he said.

Sakata also pointed out that under international law, the nation would be allowed to use the right of collective self-defense only if an ally country — presumably the U.S. — has declared its right to use individual self-defense and at the same time is requesting help from Japan.

“Japan alone could not shoot down missiles (traveling toward Guam) unless the U.S. was requesting help,” Sakata said. “It wouldn’t be recognized as use of the right of collective self-defense under international law.”

Article 9 stipulates that “the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes.”

The government has long argued that despite Article 9, a war strictly limited for the purpose of self-defense is allowed because that is an inherent right of any independent nation.

Koda, too, agreed that the SDF would not be allowed to shoot down overflying North Korean ballistic missiles such as those described in the plan announced by Pyongyang.

But the former commander also pointed out a hypothetical scenario where the U.S. may need help from the SDF’s Aegis destroyers to shoot down a North Korean missile flying toward a U.S. target.

“Politically you shouldn’t deny any option because you can’t tell what will actually happen,” he argued.

For example, if North Korea ever detonated a nuclear device in the sky over or near Guam, the electromagnetic burst would make electronic communications impossible for hundreds of kilometers from the blast site, Koda said.

A nuclear Electromagnetic Pulse (EMP) attack disrupts electronic devices such as computers, sensors and communications systems.

If all of the U.S. Aegis ships stationed near Guam were ever to become inoperable, the U.S. would need help from Japanese Aegis destroyers to defend against North Korean ballistic missiles, Koda said.

“This time such a situation probably won’t happen. But politically (Japan) should retain some options” for using the right of collective self-defense to help the U.S., he said.

Guam hosts Andersen Air Force Base, where B-1B heavy bombers have been deployed to fly over the Korean Peninsula, and U.S. Naval Base Guam, which is home to nuclear-powered fast attack submarines.

If those bases were critically crippled, the deterrence power of the U.S. military would be significantly reduced and could seriously affect the security of Japan, Koda maintained.