But in fact, the treaty is not an alliance at all, and strictly speaking, Japan is not an ally. It is a close friend, a partner, a collaborator on the world stage. But “ally” is strictly a courtesy title.

The current treaty obligates the United States to defend Japan should it be attacked. But Japan does not have an equal obligation to help defend us if we are attacked. That is because Article 9, the war-renouncing clause written into Japan’s post-war constitution, has been interpreted as barring any kind of “collective defense.”

The newest update to the treaty are designed to promote better cooperation between the armed forces of the two countries and to lessen the burden on host communities, especially on Okinawa. The new watchword is “interoperability.” One noteworthy change moves the Japanese air defense command center from Fuchu to the big American base at Yokota. The Ground Self-Defense Forces rapid reaction forces headquarters is also to move to the U.S. Army base at Camp Zama in the interests of closer coordination.

As a young Air Force officer stationed at Yokota in the late 1960s, it seemed to me the U.S. Forces and the Japanese Self Defense Force might as well have been on different planets. In nearly two years, I never met a JSDF officer. To my knowledge there was no liaison or sharing of classified information. No contact. Nothing.

When U.S. forces dealt with Japanese, it was usually with local civilian authorities over such mundane matters as off-base housing. When contingencies arose, such as capture of the U.S. Pueblo or the shooting down of an EC-121 over the Sea of Japan, Japanese forces were not a factor in any war plans.

That began to change in the 1990s. Japan had provided billions of dollars to support the Gulf War coalition, but, consistent with its anti-war principles, provided no troops. Afterwards, Tokyo was stunned at how ungrateful Washington and others were for their generous financial support.

That became the catalyst for a slow evolution in Japan’s use of its military. The Diet passed laws that allowed Japanese troops 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, and which authorized joint research in missile defenses.

There is such a disconnect between reality and paperwork in Japan—and the gap has widened so much, that Japanese leaders are now seriously considering for the first time revising their constitution in a way that faces long-standing reality: for example, officially recognizing the Self-Defense forces, which have existed for nearly six decades. The draft revision is expected to allow Japan all the rights of self-defense, including forming alliances with other countries and deploying Self-Defense forces overseas.

Does this mean the existing security treaty will be turned into a real alliance? That is unlikely because, even though nearly 50 years have passed, memories remain of the riots surrounding the last revision of the treaty in 1960, riots that forced President Dwight Eisenhower to cancel his proposed state visit.

A lot has changed in Japan since then. The radical student movement that provided so many foot soldiers in 1960 hardly exists today. And it seems doubtful that Prime Minister Junichiro Koizumi would have to ram any revisions through the Diet at midnight, like his predecessor Nobosuke Kishi.

Koizumi has a huge majority in the Diet, and the main opposition, the Democratic Party of Japan abandoned knee-jerk opposition to the security treaty in the interests of electability.

That leaves perhaps only the tiny Social Democratic Party to carry the flag of traditional Japanese pacificism. Seiji Mataichi, the party’s secretary general, said of the latest defense agreement, “It goes beyond the contents of the U.S.-Japan Security Treaty.” Mr. Mataichi is almost certainly correct. But his party holds only six seats in the Diet.