Kyle Mizokami, National Interest: Everything You Need to Know: How Japan Could Get Nuclear Weapons
In a sea-basing scheme Japan could emulate China, France or the United Kingdom, maintaining a force of five ballistic missile submarines, each equipped with sixteen nuclear-tipped missiles. Each missile would be equipped with four 100 kiloton warheads. The one submarine on patrol at all times would be equipped with sixty-four warheads.
It is perhaps China’s and even North Korea's greatest nightmare: a nuclear-armed Japan. Permanently anchored off the Asian mainland, bristling with nuclear weapons, a nuclear Japan would make China’s security situation much more complex than it is now, and force China to revise both its nuclear doctrine and increase its nuclear arsenal.
To be perfectly clear, Japan has no intention of building nuclear weapons. In fact, it has a strong aversion to nukes, having been the only country to actually be on the receiving end of a nuclear strike on its cities. Japan’s strategic situation would have to grow very dire for it to undertake such a drastic and expensive option.
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WNU Editor: If the world "goes to hell", I was told that it would take Japan about a month to assemble their first nuclear warhead. Japan has the technology, the nuclear material, and apparently the know-how to make one. But after that it gets complicated .... testing it, making a delivery system, etc. .... it will take months (if not years) for Japan to deploy a nuclear force that would be an effective nuclear deterrent.