Thanks a lot, guys

Via The Guardian, the Associated Press reports:

Japan will use its future missile defense system to ward off an attack but not to shoot down missiles aimed at its allies, Prime Minister Junichiro Koizumi said Friday.

Japan and the United States are working on a joint defense program, spurred in part by North Korea's development of missiles capable of hitting Japan. But Koizumi told the upper house of Parliament that Japan would not be obligated to use the system to protect an allied country — such as the United States — from missile attack.

"The purpose of our country's missile defense is to intercept incoming missiles targeting Japan," he said. "We are not thinking of dealing with other missiles targeting our allies."

Some people claim that Article IX of Japan's pacifist constitution prohibits Japan from using military force unless Japan itself is attacked. But such a view seems unwarranted, given the actual text of Article IX:

Aspiring sincerely to an international peace based on order, 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. In order to accomplish the aim of the preceding paragraph, land, sea and air forces, as well as other war potential, will never be maintained. The right of belligerency of the state will not be recognized.

Shooting down a missle launched at your ally hardly strikes me as a "belligerent" act.

And with a modern, well-equipped military (euphemisitcally called "Self-Defense Forces"), the fourth-largest defense budget in the world, and an anti-missile system in the works, the "land, sea and air forces, as well as other war potential, will never be maintained" bit hasn't exactly been taken literally.

Moreover, ever since the 1951 Japan-U.S. Security Treaty, America has been officially committed to defending Japan from any attack. Even today, about 50,000 U.S. troops are stationed in Japan.

While Koizumi's statement comes in the context of talks aimed at expanding and rebalancing that relationship, Japan's security still depends in large part on American protection.

It would be nice of Japan to assist, when possible, the country that has defended it for over half a century, and defends it still.

FOLLOW-UP:
In the comments, A Guy in Pajamas brings the knowledge about Article IX:

Actually, a Japanese supreme court ruling has stated that Japan can have defensive forces, but cannot exercise the right of collective defense. So, despite what you may think about the text of the constitution, the legal interpretation is that Japan cannot constitutionally defend an ally.

The LDP [Liberal Democratic Party], led by Koizumi, is trying to change this by amending the constitution, but unless / until they are successful, shooting down a missile headed for the US will be at least questionable on constitutional grounds. I personally think the Japanese would shoot one down, given the support they've given us in Afghanistan and Iraq, but Koizumi and the LDP are already under fire for those actions. The opposition parties harp on it constantly, and they have gained a few seats in the last year, possibly due to that. The LDP needs to stay out of fights like that for now.

The good news is, Japan, unlike Canada, is interested in working with the US on missile defense. The LDP is getting into the deal now, promising not to violate the constitution, while at the same time working to change the constitution. If they are successful, then Japan will likely become a key part in defending the US from possible missile attacks from belligerent states in the region.

Noted.

ANOTHER FOLLOW-UP:
Nichi Nichi adds more helpful context.