On Oct. 3, 1946, readers of The Atlanta Constitution woke up to a shocking front-page headline: “Japan Developed Atom Bomb; Russians Grabbed Scientists.”

What followed was a detailed account of how Japan supposedly tested an atomic bomb just three days before the Aug. 15, 1945, address by the Showa Emperor that accepted unconditional surrender and ended the war. The article was essentially an interview with one Japanese source, who spoke under a pseudonym.

The source, dubbed “Capt. Tsetusuo Wakabayashi,” claimed to have witnessed an atomic explosion near Konan, North Korea, that had been detonated by the Japanese military on Aug. 12, 1945. The story was written by David Snell, a reporter who had been released from the U.S. Army’s 24th Criminal Investigation Detachment in Seoul just weeks before and was now back at his old job.

U.S. and Japanese authorities, including Harry Kelly, a science adviser to Supreme Commander for the Allied Powers Douglas MacArthur, immediately dismissed the article, saying there was no evidence to justify the story, as did other high-ranking U.S. officials and Japanese scientists at the time. Snell never revealed the true identity of his source.

Over the decades, various commentators have suggested the story was either an elaborate hoax, a misunderstanding or, possibly, U.S. propaganda designed to justify the bombings of Hiroshima and Nagasaki. No independent verification of Snell’s report has ever been made. The few investigations into the matter have concluded it’s unlikely, if not impossible, for such an event to have occurred unnoticed by the rest of the world.

However, it would later be learned that Japan’s atomic bomb program was a lot more advanced than had been publicly revealed at the end of the war. But whatever the situation was in 1945, seven decades of technological advances along with an embrace of nuclear power means that, today, no one doubts Japan has the ability to build nuclear weapons if it really wanted to. More than that, it’s a possibility that declassified U.S. reports and Japanese politicians have long acknowledged.

“Contrary to the impression conveyed by the overwhelming popular sentiment in Japan against any association with nuclear weapons, there is mounting evidence that the conservative government in Tokyo secretly contemplates the eventual manufacture of such weapons, unless international agreements intervene,” a declassified August 1957 U.S. State Department report said.

That news came as Japan was preparing to embrace nuclear power as an energy source. Prime Minister Nobusuke Kishi, grandfather of current Prime Minister Shinzo Abe, indicated Japan’s postwar peace Constitution did not forbid a strictly defensive nuclear arsenal, setting off a storm of protest and debate.

As Japan moved to rely on nuclear power as an energy source, concerns that the country might divert nuclear fuel and technology for a weapons program mounted. In 1967, Prime Minister Eisaku Sato would be forced to declare, in his Three Non-Nuclear Principles, that Japan would not possess, produce or permit the introduction of nuclear weapons. The principles were adopted by the Diet in 1971. While they have served as the foundation of Japan’s stance on nuclear weapons ever since, they were never placed within a legal framework.

Behind the scenes, however, it was less clear as to what the government policy might be. The Foreign Ministry was reluctant to sign the Non-Proliferation Treaty in 1970. It would later be revealed that a secret debate raged in the Japanese bureaucracy between 1968 and 1970 about whether or Japan should arm itself with nuclear weapons, given the fact that China now had them.

Documents showed that, in September 1969, Japan was drawing up guidelines committed to the need to have the capability to convert its nuclear technology into nuclear weapons while promoting the peaceful use of nuclear energy. Now that it was pursuing nuclear power in earnest (the first domestic commercial nuclear reactor went into operation at the 1970 Osaka Expo), worries that Japan could also embark on a nuclear weapons program were growing.

That concern was heightened at the very top levels of the U.S. government in the late 1970s, when Japan began to look seriously at reprocessing spent conventional fuel, which could potentially be turned into weapons-grade material. In February 1977, U.S. Vice President Walter Mondale (who would later become the U.S. ambassador to Japan) met with Prime Minister Takeo Fukuda about Tokyo’s plans to build a reprocessing plant. According to a declassified memorandum, the U.S. was especially concerned about what, besides commercial reactor fuel, Japan might also produce. “Reprocessing facilities which could produce weapons-grade material are simply bomb factories,” the memorandum said.

Nearly four decades after that memorandum, the nuclear waste reprocessing plant in Rokkasho, Aomori Prefecture, has yet to go into operation. Designed to reprocess spent nuclear fuel from the nations’ reactors, anti-nuclear groups and nonproliferation experts, as well as International Atomic Energy Agency officials, have expressed concern about the fact that reprocessing conventional uranium fuel will generate plutonium that Japan has no clear plan for. “Japan has about 9 tons of separated plutonium domestically. The rest is held in Europe. When the Rokkasho reprocessing plant goes into full operation, it has the capacity to produce around 8 tons of separated plutonium annually,” said Robert Einhorn, senior fellow at The Brookings Institution, at a March symposium in Washington, D.C. on Japan’s plutonium capabilities.

Much of that plutonium could be enriched further and used for potentially hundreds of nuclear warheads.

After Rokkasho goes into operation, how long would it take to produce nuclear weapons? A 2006 Japanese government report estimated it might take three to five years, and cost up to ¥300 billion.

That’s much longer than the around six months some foreign media commentators were suggesting in the 1990s. But, despite the passage of almost four decades and huge advances in technology, it echoes a January 1967 U.S. National Intelligence Estimate prepared by the Central Intelligence Agency that concluded if Japan violated international safeguards, it might test a nuclear device two years after the decision to go ahead, setting the stage for further development.

“We believe the Japanese could develop a nuclear warhead … some three to five years after the first device and have a stockpile of 75 to 100 warheads in 10 years at a total program cost of $500 (million) to $600 million,” the CIA report said.

Of course, having the ability to build nuclear weapons and possessing the necessary political will and ability to actually put them in production, test-fire them and arm the Self-Defense Forces with them are entirely different matters.

The problems are numerous and begin with domestic politics. While advocates would no doubt stress Japan would use nuclear weapons only for defense, a strong anti-nuclear sentiment running through the country, and the memories of Hiroshima and Nagasaki, would make it all but impossible for a prime minister to secure enough votes in the Diet to approve such a program in normal peacetime conditions.

The second problem is the impact such a decision would have on Japan’s relations with its Asian neighbors as well as with the United States, which offers Japan protection in the form of the Japan-U.S. Security Treaty and the nuclear umbrella.

China is Japan’s largest trading partner and relations with South Korea, despite the current tension over historical issues, are growing deeper economically and culturally. Any attempt by Tokyo to produce nuclear weapons could create a huge backlash in both countries that is sure to negatively impact the domestic economy.

Nor would the United States likely welcome a nuclear-armed Japan, especially if it led to a rupture of relations with South Korea, where the U.S. also has military bases, and antagonized China.

“Japan going nuclear could set off an arms race with China, South Korea and Taiwan. Bilaterally, assuming that Japan made the decision without U.S. support, the move could indicate a lack of trust in the U.S. commitment to defend Japan,” said a February 2009 report by the U.S. Congressional Research Service, which provides information to members and committees of Congress. “An erosion in the U.S.-Japan alliance could upset the geopolitical balance in East Asia.”

Then there is the larger issue of international trust in regards to promises regarding nonproliferation Japan has made, especially the Non-Proliferation Treaty.

“To arm itself with nuclear weapons, Japan would have to withdraw from this international nonproliferation regime,” wrote Tetsuya Endo, a former vice chairman of Japan’s Atomic Energy Commission in a July 2007 report published by The Association of Japanese Institutes of Strategic Studies. “The consequences of becoming internationally isolated are shown all too clearly by Japan’s diplomatic situation starting from the 1930s.”

Japan imports all of the uranium used for its commercial nuclear reactors, and has a series of bilateral agreements with the United States, Canada, France, Great Britain and Australia, among others. To pursue a path of nuclear weapons production risks provoking opposition in those countries and possibly cancellation of the agreements. Given that Abe’s government is pushing hard for a restart of some of the country’s idled nuclear plants, it seems remote that Tokyo would want to risk losing access to the uranium fuel that will be needed to power them.

Practical barriers are even more problematic. Japan’s plutonium and uranium are kept under IAEA watch, and the country has a long tradition of offering inspectors full cooperation. Diverting nuclear material for any purpose other than commercial use would force Japanese engineers and technicians to change transparency standards and cooperation measures that have been established with IAEA inspectors over decades, something that would quickly be noticed by the international community long before any nuclear weapons could actually be produced.

Even assuming that, somehow, enough highly enriched uranium was to find its way into a nuclear weapons program, the next problem is: how to test the weapons? Carrying out a nuclear test either above or below ground anywhere in Japan is problematic due to the lack of available testing sites. Then there’s the domestic and international uproar that would surely follow — including likely sanctions on Japan by the United Nations.

Finally, there’s the question of how to equip Japan’s military with such weapons. James Holmes, a defense analyst and professor of strategy at the U.S. Naval War College, suggests Japan could arm its diesel-powered submarines with nuclear-tipped missiles.

“The limiting factor for an undersea nuclear deterrent is the size of the boat,” Holmes wrote in an email exchange with The Japan Times. “Japanese Soryus are wonderful diesel boats but could never accommodate a ballistic missile the size of an American Trident. So Japan would have to either miniaturize a submarine-launched ballistic missile, come up with a larger launch platform or both.”

He also said he had a hard time envisioning a situation in which the U.S. would supply Japan with nuclear-armed surface ships or submarines.

“We’d essentially be abandoning nuclear-arms control and possibly setting loose an arms race in Asia,” he wrote.

“From a technical standpoint, surface ships’ survivability is in doubt in today’s environment; no sane leadership would make such vessels the centerpiece of nuclear deterrence,” he added.

Japan’s only viable immediate option if it takes the nuclear plunge is a boat firing nuclear-tipped cruise missiles — i.e., tactical nukes,” he wrote. “But things will have to get really, really bad in Asia before Tokyo goes down any of these routes — and worse before Washington helps it.”

Over the past couple of months, however, a major reason for all of the international speculation about whether or not Japan might intend to pursue its own nuclear weapons program appears to have been addressed.

In March, Japan announced it would return a large stockpile of weapons-grade plutonium and highly enriched uranium that had been stored in the country for research purposes for decades.

“This effort involves the elimination of hundreds of kilograms of nuclear material, furthering our mutual goal of minimizing stocks of highly enriched uranium and separated plutonium worldwide, which will help prevent unauthorized actors, criminals or terrorists from acquiring such materials,” Abe and U.S. President Barack Obama said in a joint statement announcing the deal at the Nuclear Security Summit in The Hague in March.

After the nuclear material arrives in the U.S., the plutonium will be prepared for final disposition. The highly enriched uranium will be reprocessed into low-enriched uranium and utilized for civilian purposes. The amount returned includes a reported 320 kg of plutonium. The exact amount of highly enriched uranium to be turned over was not announced, but unofficial estimates say it’s around 200 kg.

The deal between Abe and Obama to send the material back to America came about after U.S. pressure on Japan to do so. The reasons are twofold. First, an increasingly nervous East Asia looks at Abe and his Cabinet, many of whom have voiced support for nuclear weapons, and wonders what Japan’s intentions are. Holding on to the stockpile naturally raises questions about whether or not Japan is really planning to build a bomb.

The second concern, at least on the part of the U.S., is security at the Japanese storage sites. U.S. officials have long worried that Japan does not take the threat of possible theft at the sites, or an armed attack, seriously enough. Leaked State Department reports reveal frustrations among U.S. officials over security measures at several plants and requests for Japan to beef up its security measures, lest nuclear material or sensitive technology fall into the wrong hands.

So, the current consensus is that Japan can, but will not, produce a nuclear weapon due to the high political, social and economic costs involved — at least not in the immediate future and as long as there is no radical change in the geopolitical status quo in East Asia that Japan sees as a threat to its national interests.

The Japanese Defense Agency (now the Ministry of Defense) concluded in 1995 that the costs, political and otherwise, of building the infrastructure for a nuclear-weapons program would be exorbitant, and that the nuclear option is not a favorable one.

Better, the agency said, to keep the peace by continuing to rely on the U.S. nuclear umbrella, support the Non-Proliferation Treaty and to reform the United Nations to allow non-nuclear states such as Japan permanent membership. Nearly two decades later, despite the desire by many conservative politicians, bureaucrats, academics and media favoring Japan going nuclear, the price still remains too high.

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