HONOLULU — Take a deep breath and repeat: “Japan is not going to develop nuclear weapons.” Feel better?

Yes, North Korea’s nuclear test is a blow to the regional security order. It is a bitter defeat for diplomacy. And yes, Japanese (and Chinese and Americans and South Koreans and others) are concerned about its implications, but the fear — the assumption — that Japan will develop its own nuclear weapons as a consequence is pure fantasy.

Japanese understand that the nuclear option is a last-gasp desperate move that will create more instability and insecurity than it will eliminate. To be sure, North Korea’s test complicates Japanese national security planning, compounds popular insecurities, and provides ample fodder for conservatives and nationalists who demand a more robust defense posture. It will certainly be cited by Prime Minister Abe Shinzo and others as they campaign to revise Japan’s Constitution.

In 1994, then-Prime Minister Tsutomu Hata admitted that “Japan has the capability to possess nuclear weapons.” But capabilities alone do not determine a country’s security policy; intentions are even more important.

Japan still lacks the will to develop nuclear weapons — and for very good reasons. Perhaps most powerful is the resilience of the nuclear taboo in Japan. The experience of World War II is still strong in the popular consciousness, and the Japanese public remains highly resistant to the thought of developing its own nuclear weapons capability. (Expect a deluge of polls on this topic in the near future but look closely at the wording of key questions.)

Significantly, Japanese security planners recognize that a national nuclear arsenal would be destabilizing and would actually diminish Japanese security. Building a Japanese bomb would further erode the global nonproliferation order, would generate greater mistrust among neighbors, and raise questions from allies about its strategic intentions.

This is the logic animating former Prime Minister Yasuhiro Nakasone’s recent call for a national study of the nuclear option. He is not endorsing this course, as he explained, “The first priority is to keep being a nuclear-free state, and the second is to reinforce the system under the Nuclear Nonproliferation Treaty (NPT).” But he understands that a national debate on the subject is good for Japan. It will lay the foundation for a stable and credible national security policy and help establish the consensus needed to implement it.

Japanese must ask how a North Korean nuclear weapon changes the security landscape. It adds a new wrinkle, but it is hard to see how Pyongyang’s bomb transforms it in any fundamental way. The U.S. nuclear umbrella is still in place, and it is unclear why deterrence wouldn’t work against North Korea — with a tiny arsenal — when it worked so well against the Soviet Union despite its inventory capable of destroying the world several times over.

In fact, Japan has already studied the nuclear option. In the 1960s, the Sato Cabinet examined the possibility, and used the willingness to proceed down that path to secure a place under the U.S. nuclear umbrella. Some three decades later, a study conducted at the behest of the Japan Defense Agency after the first Korean nuclear crisis concluded that a Japanese nuclear arsenal would make little strategic sense, as it would:

Damage the country’s image

Undermine the NPT

Prompt countermeasures by other countries in the region (including development of their own nuclear arsenals)

Threaten the alliance with the U.S. (by raising questions about the need for a U.S. commitment to Japan if Tokyo could defend itself)

Provide very little security for Japan in return. The country is too small, the population too concentrated. Thus it would remain vulnerable no matter who had their finger on the trigger.

That logic hasn’t changed. A nuclear weapon wouldn’t add to Japan’s defense capability but would do real damage to its core security interests. To their credit, the Japanese recognize that.

As Abe explained to a Diet committee early last week: “We have no intention of changing our policy that possessing nuclear weapons is not our option. There will be no change in our nonnuclear arms principles. We want to seek a solution through peaceful and diplomatic means.”

The only wild card is the American commitment to Japan’s security. If Tokyo felt the Washington was wavering, then a homegrown bomb might make some sense.

The answer, then, to growing unease after North Korea’s test is for both the U.S. and Japan to continue efforts to strengthen the alliance. To their credit, they are doing that.

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