The people of Japan live in a dangerous neighborhood. China is bristling with new missiles and an ever-expanding nuclear weapons capability. North Korea has tested new missiles and, in defiance of the international community, a nuclear weapon. Making matters worse, South Korea often appears to be complicit with North Korea, perhaps because Seoul foresees the day when it will take possession of the North's arsenal.

Yet, Japan has not developed its own nuclear arsenal, even though it has the capability of doing so quickly. Just after North Korea's nuclear test last year, Tokyo reconsidered whether to build its own nuclear weapons. But it decided against doing so after seeking and obtaining a high-level U.S. restatement of American commitment to use U.S. nuclear forces in defense of Japan.

Thus, U.S. nuclear weapons play a key role in nuclear nonproliferation. And Japan is not the only nation that relies on the U.S. nuclear umbrella. The "White Paper on the Necessity of the U.S. Nuclear Deterrent" (prepared by a subgroup of the U.S. Department of State's International Security Advisory Board and released July 30) points out that the U.S. has extended security assurances to 31 countries — the 26 nations of NATO, Australia, Japan, South Korea, Taiwan and Israel. Most of these countries could "go nuclear," but haven't because of the umbrella.

The white paper also points out that the countries, such as Japan, that depend on the U.S. nuclear umbrella have the right and the responsibility to insist that the weapons that defend them be modernized and tailored to the task. For example, if use of U.S. nuclear weapons should become vital, the Japanese may want weapons that inflict the least destruction, loss of life and collateral damage. Or, Japan may consider it important to be able to destroy key underground nuclear facilities in North Korea.

Current U.S. nuclear weapons have not been modernized to meet current requirements. For example, they are not designed to take out deeply buried targets, such as those in North Korea, with minimal nuclear fallout.

U.S. nuclear weapons are high yield and were designed to destroy hardened missile silos and vast military infrastructure in the Soviet Union. Furthermore, U.S. delivery vehicles are primarily long-range, whereas defense of Japan might be better served with tactical-range missiles.

A related problem is that U.S. weapons have not been tested since 1992. How can we be sure that they will work as intended? U.S. weapons components, made brittle by subjection to radiation, could fail. Also, U.S. weapons that are being refurbished to extend their shelf life are likely to suffer from flaws unknowingly introduced during remanufacture.

Scientists, military officials, and politicians all assure us that the weapons will work, but privately, they admit that only nuclear testing would reveal that for sure. In this context, it is important to keep in mind that extremely low-yield testing can assure reliability.

This analogy is not perfect, but it may illuminate. Imagine that you are going to enter a car race that will involve high speeds. Your life may be at stake, depending on the performance of your car. You are offered a vehicle that has been sitting in a garage for almost 15 years without being driven. College-graduate engineers have gone over the car and pronounced that it will work well, but they have not been allowed to modernize it or test it.

How comfortable would you feel getting behind the wheel and racing it? If you wouldn't trust such a car with your life, why would you trust your life — and your nation's existence — to the defense offered by an aged, untested, unmodernized nuclear arsenal?

Japan does not have to rely on an old, unsure nuclear umbrella for its defense. One alternative would be to develop its own nuclear arsenal. But that has serious political downsides.

Another, easier option would be for Japan to insist that the U.S. arsenal be made more effective and sure. At a minimum, Japan has the right to provide input on the quality and quantity of the U.S. nuclear arsenal for the future.

Kathleen C. Bailey is a member of the U.S. Department of State International Security Advisory Board. She lives in Anahola, Kaua'i. She wrote this commentary for The Advertiser.