Photo/IllutrationThe next-generation interceptor missile SM-6 is expected to better track cruise missiles. (From the website of the U.S. Missile Defense Agency)

With an eye on China, the government is considering expanding its capabilities to intercept not only ballistic missiles but cruise missiles under the nation's new defense program guidelines.

The plan is expected to bring Tokyo and Washington even more closely together under the envisaged missile defense system, or the Integrated Air and Missile Defense (IAMD), laid out by the U.S. military.

“(The move) is partly intended to bolster Japan’s defenses against North Korea’s ballistic missiles, but the real aim of introducing the IAMD is to counter China, which has been upgrading a number of its missiles,” said a senior official with the Self-Defense Forces.

But some government officials expressed concerns that joining the IAMD could violate the principle of the nation’s pacifist Constitution. They also voiced skepticism on how effective it would be in shooting down sophisticated missiles and the huge amount of funding required.

The revision of the National Defense Program Guidelines is expected at the end of next year.

Prime Minister Shinzo Abe signaled the need for a sweeping overhaul of the existing defense program guidelines during a speech on Dec. 15.

“We want to gauge the necessary defense capabilities our country should have to protect people, not just the extension of the existing guidelines, while facing up squarely to the stern reality surrounding Japan,” he said.

Defense experts say it is relatively easy to calculate the trajectory of a ballistic missile as it, in principle, flies in a parabolic curve.

But shooting down a cruise missile would pose greater problems. A cruise missile can change course in flight and is also harder to detect on radar as it travels at a low altitude.

The government is leaning toward the introduction of the IAMD because it believes the nation should be equipped with the ability to defend itself from a possible attack by cruise missiles, on top of North Korea’s ballistic missiles.

China, as well as Russia, has been stepping up efforts in recent years to develop a longer-range cruise missile that can fly at Mach 5 or faster.

The U.S. Defense Department announced the IAMD in 2013 as a defense mechanism against an adversary’s cruise missiles and drones. It plans to realize the system in 2020.

At the center of the IAMD is the SM-6, the next-generation interceptor missile. The SM-3 missiles deployed on Aegis-equipped destroyers can target only ballistic missiles.

But the SM-6 is expected to be capable of intercepting cruise missiles if they are introduced to Aegis destroyers and the so-called Aegis Ashore, the land-based version of the missile defense system.

The government plans to ask for 2.1 billion yen ($18.6 million) for purchasing test ammunition of the SM-6 in its budgetary request for fiscal 2018.

But some government officials are concerned about the push to adopt the IAMD system.

For starters, firing missiles by the SDF’s Aegis destroyers based on intelligence obtained by the U.S. military’s early-warning aircraft could breach Article 9 of the Constitution, which forbids the nation’s use of force in a manner integrated with other countries.

In addition, questions will remain over the effectiveness of IAMD technology in shooting down missiles that are becoming increasingly sophisticated.

The new system’s huge price tag is also expected to provide a major headache for the government.

(This article was written by Ryo Aibara and Senior Staff Writer Taketsugu Sato.)