Could Tokyo ever go critical and make nuclear weapons?

Seventy-three years ago on Monday, the world entered the nuclear age when Hiroshima was vaporized with the first atomic bomb ever to be detonated over a city. The anniversary was marked with a somber ceremony at ground zero attended by Japanese Prime Minister Shinzo Abe.

The trauma of the destruction of Hiroshima, and three days later, Nagasaki, with a second nuclear bomb, has never lifted from Japan’s consciousness. Anti-nuclear sentiment remains strong; even hard-liner Abe has repeatedly said – including on Monday – that Japan will not possess nuclear arms.

But the country lives in dangerous geopolitical territory, and a recent report states that Japan has enough plutonium to make up to 6,000 nuclear weapons.

How might Japan respond if North Korea refuses to denuclearize? Tokyo has discussed a first strike capability in the past and various policymakers, on various occasions, have broached the subject of developing atomic arms.

The notion that Tokyo, despite repeated denials, might develop its own nuclear weapons is not entirely far-fetched – particularly when Japan’s past efforts in the field of nuclear weapons development is examined.

Japan’s shadowy nuclear history

It was not until after World War II that Japan’s very own atomic bomb project became known. Even today, it is now well known that Tokyo was developing its own atomic bomb.

Actual work on a Japanese bomb started in 1942, and two such projects were briefly active at the same time: one by the army, the other by the navy. Bitterly competitive with each other, the two programs merged toward the end of the war.

There is disagreement among historians as to whether the Japanese effort was close to fruition. What matters is that one Japanese nuclear scientist avowed: “If we’d built the bomb first, of course we would have used it.”

Fortuitously for the Allies, US B-29 bombers targeting Tokyo on the night of April 9-10, 1945, destroyed key uranium-refining components.  And a German U-boat ferrying 560 kilograms (1,230 pounds) of uranium oxide intended for Japan surrendered in the Atlantic shortly after Germany capitulated in May 1945, depriving the Japanese program of much-needed fissile material.

Hiroshima and Nagasaki

Controversy continues to rage over whether the US needed to use atomic bombs on Japan to bring World War II to an end. Two books by American historians, complete with meticulous documentation, detail what Allied leaders knew when they were planning the inevitable invasion of the main Japanese islands. Anyone wishing to familiarize themselves with the topic needs to read them.

The first book, Weapons for Victory: The Hiroshima Decision Fifty Years Later, by Robert James Maddox, thoroughly discredits many misinterpretations of documents that have led to egregious second-guessing regarding the need for the weapons. The second, Downfall: The End of the Imperial Japanese Empire, by Richard B. Frank, assesses US military intelligence that calculated a substantial – but still greatly undercounted – build-up of Japanese forces exactly where Allied commanders had planned the invasion of Kyushu, the southern-most mainland Japanese island.

The actual strength of the Japanese defenders – far greater than US intelligence estimates – is established in the book Racing the Enemy: Stalin, Truman, and the Surrender of Japan, by Japanese-born historian Hasegawa Tsuyoshi.

In consideration of how Imperial Japanese forces largely fought to the death as the Allies advanced across the Pacific to the Japanese mainland, and in view of the fact that the defensive forces on Kyushu had been seriously underestimated, any Allied invasion would have been a massive bloodbath. This suggests that the bombs were, indeed, necessary.

The “Jewel Voice Broadcast,” a recording of Emperor Hirohito that aired at noon on August 15, 1945 (Japan Time), announcing Japan’s capitulation to his people, speaks to that point. The emperor cited the destructive power of a new weapon – the American atomic bomb – and stated that continued fighting would “result in an ultimate collapse and obliteration of the Japanese nation.” The emperor accepted unconditional surrender to “save the millions of our subjects.”

Japan’s intentions today and tomorrow

Was that submission truly the end of Japan’s nuclear weapons ambitions? Japan’s current inventory of weapons-grade plutonium is thought to be roughly 47 tons – about 43 metric tons. Except for the “starter” fissile material from the US, all of that plutonium was gained by harvesting spent fuel rods from Japan’s electrical power plant reactors.

Equally important, Japan has had an actual nuclear weapons policy since 1969 – although that had been secret until 1994 when it was leaked. The leaked document states in part that “for the time being we will maintain the policy of not possessing nuclear weapons,” but “keep the economic and technical potential for the production of nuclear weapons, while seeing to it that Japan will not be interfered with in this regard.”

Known as technical deterrence, this wording allows Japan to claim adherence to the nuclear Non-Proliferation Treaty (NPT) by not possessing nuclear weapons, while at the same time demonstrating that it has the intent to produce them if and when needed.

Paragraph 1 of Article X of the NPT states:

Each Party shall in exercising its national sovereignty have the right to withdraw from the Treaty if it decides that extraordinary events, related to the subject matter of this Treaty, have jeopardized the supreme interests of its country. It shall give notice of such withdrawal to all other Parties to the Treaty and to the United Nations Security Council three months in advance. Such notice shall include a statement of the extraordinary events it regards as having jeopardized its supreme interests.

Contrary to widespread popular belief, Japan’s post-war constitution does not specifically prohibit the possession of nuclear weapons. It is Japan’s Basic Atomic Energy Law of 1956, and its associated national policy, that establishes the three non-nuclear principles: no possession, no manufacturing and no nuclear weapons in the country.

However, both statute and policy can be easily changed. Any “extraordinary events” that would justify Japan leaving the NPT could trigger such changes. North Korea’s refusal to rid itself of nuclear weapons and missiles that can reach Japan could constitute the extraordinary events of Article X.

While the political will may be absent at present, Japan clearly has the material, the technical ability and the economic capacity to manufacture nuclear arms.

Expert estimates of how long it would take Tokyo to deploy a nuclear weapon vary from six months to five years – a range so wide as to be uninformative. Given this, it is intriguing that American Vice President Joe Biden told China’s Xi Jinping in 2016 that North Korea’s nuclear program had to be reined in since Japan could build its own nuclear bomb “overnight” – something Beijing is strongly opposed to.

Now, the previously absent political will may appear. Not only is North Korea clearly dangerous, but allies are questioning Washington’s defense commitments, particularly the steadfastness of its nuclear umbrella in Northeast Asia. Japan may soon feel compelled to put its “technical deterrence” into practice.

Even if, as recently stated, Japan intends to reduce its stockpile of plutonium, it would still have enough material for several nuclear weapons.