The turbulent and traumatizing experience of that week has led analysts to conclude for over six decades that Japan would never “go nuclear” and develop its own bomb. Indeed, this has been reinforced by Japanese actions. Japan is a leading advocate of the Non-Proliferation Treaty (NPT) that allows only five nations (United States, United Kingdom, Russia, France, and China) to possess nuclear weapons and every year introduces a resolution in the United Nations calling for global nuclear disarmament.

There is, however, another side to Japan’s position: As North Korea grows increasingly provocative and China continues to build up its nuclear forces, Japan has found itself confronted with a more threatening security environment. Moreover, drastic reductions in the U.S. nuclear arsenal, brought about by arms-control treaties with Russia, have heightened Tokyo’s concern about the reliability of the U.S. nuclear umbrella. As one Japanese official has commented, “We could afford to sleep during the Cold War; we cannot afford to sleep now.” The previous taboo on even discussing a Japanese nuclear deterrent has already been broken, as prominent Japanese lawmakers and politicians debate the option in response to North Korean and Chinese actions.

Tokyo justifiably feels threatened by Pyongyang and Beijing. At the same time, it is almost completely dependent on Washington for deterrence. Japanese officials stated to the Strategic Posture Commission that the credibility of the U.S. nuclear umbrella was dependent on its “specific capabilities to hold a wide variety of targets at risk.” Japan was greatly concerned when President Bush cut nuclear warheads to 2,200. If President Obama cuts warheads to below 1,700, and without consulting Tokyo, as outlined by the Strategic Arms Reduction Treaty (START agreement), Japanese officials may perceive the U.S. "extended deterrent" to be insincere and unreliable.

And what if Japan decided to go nuclear? The consequences would be far-reaching:

First, it would be a major blow to the NPT. Japan has served as the epitome of nonproliferation and, as the only victim of nuclear attack, carried a moral authority in its calls for nuclear disarmament. Without that voice, the NPT becomes a largely meritless system of haves and have-nots. Second, a nuclear arms race would seem almost inevitable. Not only would China and North Korea respond by ramping up capabilities, but South Korea and Taiwan might be compelled to go nuclear as well. The spillover effects would likely ratchet up the arms race between India and Pakistan, too.

Of course, on the flip side, Japan seems to have every reason to remain non-nuclear. As Takashi Yokota of Newsweek has argued, less than a fifth of Japanese citizens support building the bomb, the island nation lacks the physical space to test a nuclear weapon, and it is dependent on nuclear fuel (supplied by the United States, Australia, and Canada) for about a third of its electricity.

Not only is it therefore impractical for Japan to go nuclear, but the resulting arms race and cutoff of its fuel sources would likely leave Japan much less secure than it is now.