First, a little housekeeping, then onto the subject of Japanese nukes. In the comments section of my previous post on the Sankei article, I posted the full text in Japanese. Two readers have offered translations, which I think is a model use of the comment section. In that spirit, I am going to start posting the full text of various news articles relevant to posts in the comment section, rather than as text files.

I wanted to check into something that Jane noted—the strange persistence of the idea that Japan was merely “six months” away from a bomb.

It’s not, never has been, and—for all I know—never will be.

Japan’s Nuclear Capabilities

The Government of Japan has twice commissioned these kind of studies—once in 1968 and then again in 1995.

  • In 1968, Japanese Prime Minister Eisaku Saito—acting through the Cabinet Information Research Office—commissioned for nongovernmental academics to examine the costs and benefits of an independent Japanese deterrent. Yuri Kase, who managed to acquire a copy of the document, provides the definitive account of the document in “The Costs and Benefits of Japan’s Nuclearization: An Insight into the 1968/70 Internal Report”, The Nonproliferation Review 8:2, Summer 2001, pp. 55-68. Kase, unfortunately, focuses on the second portion of the article, rather than the first, which enumerated the contemporary technical and economic hurdles faced by Japan.
  • The Japan Defense Agency commissioned a 1995 study entitled, A Report Concerning the Problems of the Proliferation of Weapons of Mass Destruction “because of growing concerns in neighboring nations that Japan was preparing to go nuclear in response to” North Korea’s nuclear program—although the document was presumably also linked to Tokyo’s decision to support indefinite extension of the NPT that year. (See ”’95 Study: Japan and Nukes Don’t Mix,” Asahi News Service, February 20, 2003, posted in the comments section, and Michael J. Green and Katsuhisa Furukawa, “New Ambitions, Old Obstacles: Japan and Its Search For an Arms Control Strategy,” Arms Control Today, July/August 2000, link.)

What is different about the September 2006 report—based entirely on the Sankei Shimbun article—is that seems to focus on how, without any discussion of the strategic costs.

That worries me, at least a little.

The estimate—$1.7-2.5 billion over 3-5 years—however, is reassuring and broadly consistent with other estimates.

The best technical discussion that I know is a chapter in a book by the Stimson Center. [Jeffrey W. Thompson and Benjamin L. Self, “Nuclear Energy, Space Launch Vehicles, and Advanced Technology: Japan’s Prospects for Nuclear Breakout,” in Japan’s Nuclear Option: Security, Politics, and Policy in the 21st Century, Benjamin L. Self and Jeffrey W. Thompson, editors (Washington, DC: Henry L. Stimson Center, December 2003) pp.148-176.] Although Thompson and Self don’t make cost or timeframe estimates, they conclude that Japan remains “far” from a nuclear weapons capability based on arguments very similar to those that appear in the Sankei story—in particular, the emphasis on eschewing use of plutonium produced in Japan’s light water reactors and the difficulties associated with developing a feasible delivery system.

Overall, I think the leak of the government report is an interesting illustration of why a potential proliferator might make longer estimates than we see in the popular press. It is easy, as a talking head, to claim that you just grab some reactor fuel and turn a couple of screws. But, as a government official advocating an expenditure of the billions and a significant change in security policy, you probably want to do the job right. That means serious fissile material and real attention to engineering a warhead and a missile that would work together.

It is precisely these kind of concerns—how far a latent or virtual nuclear power really is from a bomb—that quietly inform very different assessments of the threat posed by Iran’s nuclear program. I would also add that Japan’s emphasis on a graphite moderated heavy water reactor is precisely why the Iranian reactor at Arak freaks me out.

A second estimate of Japan’s nuclear capabilities, one that I would love to acquire, is cited in the chapter on Japan by Kurt Campbell and Tsuyoshi Sunohara in The Nuclear Tipping Point: Why States Reconsider Their Nuclear Choices. Here is the citation:

Japan: Technical Paths to a Nuclear Detterence Background: Questions and Answers (Arlington, VA: CENTRA Technology, December 2003).

I think it is interesting that the arguments in the estimate described by Sankei remain the same as those made in classified US intelligence estimates from the 1960s and 1970s. A 1967 National Intelligence Estimate predicted that it would take Japan 3-5 years and 500-600 million dollars (about 2.8-3.4 billion in current dollars) to develop a nuclear warhead for use on a ballistic missile. [Those estimates were also broadly consistent with the best unclassified analysis of the issues, John Endicott’s Japan’s Nuclear Option: Political, Technical and Strategic Factors (New York, NY: Preager, 1975).]

The bottom line is, and has been for some time, that Japan has made large investments in a civilian nuclear power industry, without developing the sort of expertise that would allow the quick assembly of a nuclear device, or the production of delivery vehicles. At least, not inside six months.

Right, So Where’d They Get the Six Months?

Given all this, one kind of wonders how the crazy “6 month” idea became so persistent. One sees these kind of assessments all the time in the literature:

  • Andrew Mack observed that “Estimates of the time it would take Japan to produce nuclear weapons vary from a few months to a year …”
  • Richard Tanter told reporter Tim Johnson that “Every country in the region knows [Japan] can produce a nuclear device, a rather sophisticated one, probably in six months.”
  • Richard Halloran quoted a “Japanese strategic thinker” as saying that “Japan is N minus six months”—“meaning it would take only six months to build a nuclear device after a decision had been made.”
  • Paul Leventhal told Geoff Brumfiel that Japan was little more than “a screwdriver away” from a nuclear weapon. “Most [countries] think it could get a bomb in a matter of weeks to months, if not days.”
  • Ariel Levite claimed that Japanese policy has allowed “Japan to remain within a few months of acquiring nuclear weapons.”

I have tried to find the origin of the “six month” estimate—but to not much avail …

Levite is the only person to provide evidence for the estimate—a well known January 1994 story in the Sunday Times by Nick Rufford (posted in the comments), citing British Ministry of Defense report that claimed Japan had all the components necessary for a nuclear weapon:

JAPAN has acquired all the parts necessary for a nuclear weapon and may even have built a bomb which requires only plutonium for completion, according to a secret government report [from the Ministry of Defence to the Joint Intelligence Committee].


The report, sent last month, reveals that Japan has key bomb-making components, including plutonium and electronic triggers, and has the expertise to ‘’go nuclear’’ very quickly.

One expert who has seen the report said: ‘’They (the Japanese) could have acquired all the expertise for imploding a weapon without breaking safeguards. All they would need to do is select adequate amounts of plutonium for the core.’’

Levite doesn’t really focus on the credibility of the claims, especially the issues of using spent reactor fuel and the question of a delivery vehicle—issues central to the 3-5 year estimate. Nor does the Sunday Times actually say “six months.”

A second hint is a claim that Japan is the claim that Jane mentioned—that Japan is within “183 days” of constructing a nuclear weapon (that is one half of 365, rounded up … or six months). This is variously attributed to a senior Japanese official, defense official or politician.

Zhu Minquan provides the first reference that I have seen to the 183 day claim—although Zhu cited an article called “Exposed by Japanese Mass Media, Japan Can Make Its Atomic Bombs with 183 days” that comes from this not very reputable site. Sadly, no link to the Japanese mass media in question.

A little lexis-nexis action reveals the second earliest reference—a 2002 Straits Times analysis describing remarks by Tang Zhongnan, president of China’s Institute of Japan Studies, who reportedly claimed that a Japanese magazine Diamond Weekly in 1995 quoted “a senior Japanese official” claiming that “Japan could produce a nuclear weapon within 183 days.”

Ehsan Ahrari also in September 2004 attributed the remark to “an unnamed Japanese politician” in a July 1995 issue of the Japanese magazine Hoseki Gem—which is also how the People’s Daily sourced the story a few months earlier (although it attributed the quote to “a senior Japanese government official).

The real prize, however, goes to Neil Weinberg, writing with Kiyoe Minamiin in the September 5, 2005 edition of Forbes magazine. Weinberg describes the claim as having occurred “recently,” leaving the impression he heard the remark:

When asked recently whether Japan could go nuclear and, if so, how long it would take, a defense official replied that such a move would be constitutional but that Japan has no intention of doing so. If it did, he added, it would take 183 days.


No one actually seems to have posted a copy of the original article where the claim was made or provided a full citation. I am willing to be that no one on this list has actually seen the Japanese magazine article. I am even beginning to wonder if it exists at all. (Or, if it is going to turn out to be totally disreputable). The only thing I can say is that the originators of the claim clearly seem to be in China.

Either way, the “six month” estimate seems to be much older than either the Sunday Times story or the “183 day” claim. The oldest mention of the “six month” idea that I can find is from 1986, when David Fairhall in The Gaurdian quoted a “local expert” as claiming that Japan had “the technical capacity to produce a nuclear bomb in six months”—although Fairhall was trying to make a rather less alarmist point about the Japanese “nuclear allergy.”

Having looked at the technical reasons that Japan is several years away from a deliverable nuclear warhead and the strange persistence of the “six month” idea—it is hard not to conclude that “six months” is a wonky equivalent of the Biblical Forty. “Six months” is a rough estimate—on par with “a screwdriver’s turn” as the Leventhal quote suggests—intended to make the wonk look smart and satisfy hungry journalists.

The only problem is, it ain’t true.