There has been considerable handwringing in the western press, especially among Americans, over the future of the U.S.-Japan military alliance under the new regime. Will Japan’s new masters seek to undermine the security of Asian and American interests by steering a more independent course?

Never mind that the incoming prime minister Yukio Hatoyama has stated that the alliance is fundamental to Japan’s security and that he has no intention of undermining what pundits on both sides of the Pacific persist in calling the “cornerstone” of America’s position in Asia.

A cornerstone, perhaps, but not an alliance. Japan is a close friend, fellow democracy, trading partner and increasingly a collaborator on the world stage. But it is not an ally. That is strictly a courtesy title, and since the health of the “alliance” is going to come under increasing scrutiny in coming months one should have a clearer idea of what it really is.

The Treaty of Mutual Cooperation and Security, signed with Japan in 1960 to replace an earlier treaty, is basically a deal. The US promises to defend Japan if it comes under attack, with nuclear weapons if necessary (the nuclear umbrella). In exchange, Japan provides the US with bases which it can use as it sees fit to advance its greater security interests in Asia and as far away as the Middle East.

Those bases are not necessarily designed, or at present even configured to merely defend Japan. In the past they have been staging areas for the Vietnam War and now the Afghanistan War. The largest air base near Tokyo, Yokota AFB, for example, hasn’t had a permanent collection of attack aircraft or interceptors for decades.

Japan, however, is not obligated to come to the defense of the US if it is attacked. Indeed, it would be illegal for Tokyo to do so under the current liberal interpretation of its American-written constitution, which rather explicitly prohibits Japan from possessing any military force whatsoever.

This provision – Article 9 – has been interpreted broadly enough to permit Japan to build one of the largest and most sophisticated militaries on the globe. But the clause has still been interpreted in such a way as to prevent “collective defense” In other words, Japan can defend itself but not others.

Nobody worried much about collective defense during most of the Cold War, when the Soviet Union was considered the main threat. But it has grown into an issue with the emergence of a bellicose nuclear-armed North Korea and to a lesser extent, the rapid modernization of China’s armed forces.

North Korea’s recent test of a multi-stage rocket in April, which it fired directly over Japan to land in the North Pacific, raised the interesting speculation whether Japan could legally shoot down a North Korean missile headed toward the US that came within range. A strict reading of Japan’s laws would say no.

In another hypothetical but possibly more realistic scenario, North Korean naval vessels intercept and threaten to sink or capture an unarmed or lightly armed American naval surveillance ship in international waters of the Sea of Japan. A Japanese destroyer happens to be close by. Does it come to the American vessel’s aid?

I would be willing to guess that Tokyo would order the destroyer to resist the North Koreans and let the legal chips fall where they may. The consequences of simply standing by and doing nothing would be politically devastating. The American public would never understand – or care about - the legal nuances of “collective defense.”

(In the real USS Pueblo incident in 1968, in which North Korea captured a US spy ship and held its crew captive for 11 months, the Japanese Self Defense Forces did not figure at all, nor, to my knowledge, were they called on for help. The U.S. had more assets in the region than it does now. That they could not be successfully deployed to defend the Pueblo from humiliating capture is another story).

When I came to Yokota as a junior officer shortly after the Pueblo Incident, US forces in Japan and the Japanese Self Defense Forces might as well have existed on different plants. In all my time there I never once met a SDF officer. There was no liaison or coordination. No contact that I could see. Nothing. I never served in a NATO country, but I have to believe that there would have been much more social or professional intercourse with officers of the Royal Air force or the Belgian Air Force.

That began to change in the 1990s, the catalyst being the1991 Gulf War. Japan ponied up billions of dollars to support the coalition, but, consistent with its anti-war principles, provided no troops. Tokyo was stunned afterwards at how ungrateful Washington and others were for their generous financial support. They wanted, to use the current vernacular, boots on the ground.

That began a slow evolution in Japan’s use of its military. The Diet (parliament) passed laws that allowed the Japanese to participate in international peacekeeping missions in Cambodia and elsewhere. In 1996 Washington and Tokyo inked the Joint Security Declaration in which Japan promised to provide logistical support for U.S. forces stationed in Japan. Joint research in missile defenses was authorized.

In recent years Japanese armed forces have ventured far from Japan. For some years, a naval oiler has replenished ships, including American naval vessels, supporting operations over Afghanistan. But this had nothing to do with any kind of treaty obligation but more a general sense that Japan had to do something more in the War on Terror than write checks.

The defeated Liberal Democratic Party (LDP) made changing the law to permit collective defense one of its manifesto planks. The triumphant Democratic part of Japan (DPJ) was silent on the matter. Speaking to journalists a couple months before the election, senior party leader Seiji Maehara dismissed the North Korean missile hypothetical as an “abstraction.”

This year, though, the Diet passed a law to formally authorize the Japanese Maritime Self Defense Force (navy) to take part in anti-piracy patrols off the coast of Somalia. As part of the legislation, Japanese warships were specifically authorized to come to the aid of non-Japanese vessels threatened by pirates. That may seem like an obvious thing, but in a sense it was revolutionary. It was the first time that Japan had taken a baby step toward collective defense.