A man walks past a street monitor showing North Korea's leader Kim Jong-Un in a news report about North Korea's nuclear test, in Tokyo, Japan, on Photo: Reuters / Toru Hanai

When I was a correspondent in Tokyo in the late 1980s, one of the lighter anecdotes about Japan developing its own nuclear weapons concerned a foreign reporter’s interview with a Japanese defense official. Queried on how long it would take Japan to build a nuke if it absolutely had to, the official launched into a circumloquacious discourse. He said it would be unthinkable due to public opposition, unthinkable for a crowded nation within easy range of Chinese missiles to engage in a nuclear arms race, and so forth.

As he did this, the official silently traced the number “6” with his finger on the table in front of him – for six months. That’s how long he estimated it would take Japan to fashion a bomb from reactor-grade plutonium taken from one of its nuclear power plants.

Fast forward to 2017, and the unthinkable has become publicly thinkable. There’s widespread debate in Japan about whether the country should go nuclear – either by developing its own arsenal, or sharing such weapons with the US under a “dual key” arrangement, popularly known as “rent-a-nukes,” to counter the growing threat from North Korea.

Rather than fussing with the technology and cost of developing its own missiles and warheads, some say it’s far more sensible for Japan to negotiate a nuclear-sharing option with Washington. Such cooperation would also bind the US and Japan closer and head off future trouble in the bilateral military alliance.

Realistic option?

Masahiro Matsumura, a professor of international politics and national security at St. Andrew’s University (also known as Momoyama Gakuin Daigaku) in Osaka, is a proponent of the idea.

“Nuclear sharing is the best practical option when one considers the evolving realities under existing constraints,” Matsumura told Asia Times in an email interview.

Under his plan, the US would store tactical nuclear missiles and bombs at US bases in Japan. The US military would turn them over to Japan if military action, such as a strike against North Korean bases, was deemed necessary. Nuclear-tipped US Tomahawk cruise missiles and other nukes could be delivered by Japan’s extensive force of conventional submarines and warplanes.

He says the US would be responsible for the security of these devices while they were stored in Japan and that adequate safety controls would be in place to prevent unauthorized arming and detonation. The US would presumably have final say on when such weapons are used.

Under current policy, no US tactical nukes are stored at US bases in Japan or South Korea.

The Rokkasho nuclear fuel reprocessing plant in Japan’s Aomori prefecture.

Matsumura says his nuke-sharing plan has compelling benefits for Japanese security. First, it would reduce the chances of a “decoupling” of the US-Japan security alliance. Second, since Japan isn’t developing its own nukes, it won’t be in violation of the international Non-Proliferation Treaty (NPT) designed to stop the spread of nuclear weapons.

“Should Japan itself go nuclear, that will surely devastate the integrity of the NPT regime, which Japan sees as satisfying its long-term national security and global economic interests,” Matsumura said.

The security expert points to doubts in Japan about how far Washington will go in defending Japan now that Pyongyang has a long-range missile that threatens the US mainland.

An abrogation of the US-Japan security treaty and a decision by Japan to become a self-reliant nuclear power, on the other hand, carries other risks. “A nuclear-armed Japan would have to redefine its strategic relations with the US – it’s sole guarantor,” Matsumura said. “This might require a significant modification of the bilateral alliance relationship at the very least or an abrogation of the alliance at the very worst.”

Given Japan’s concerns about a North Korean threat and China’s rising military power, Matsumura argues that nuclear sharing with the US is the most realistic option.

Use NATO guidelines

Matsumura’s plan assumes that acceptable guidelines governing the use of such weapons can be agreed on between US and Japanese officials. He notes an earlier US precedent of allowing tactical nukes to be transferred to non-nuclear NATO members such as Germany in the event of war.

He thinks similar rules can be created between Japan and the US. “Japan will most likely emulate the NATO precedent,” Matsumura said. “This is not a choice but a necessity, given that the country possesses little know-how regarding practical details in possession, security, maintenance, and procedures involving nuclear warheads.”

The US has also cooperated in the past in helping close allies develop nuclear capabilities. Analysts note the US helped Britain to develop its own fleet of nuclear-armed Polaris missile submarines in the 1960s. Seoul and Washington are also seriously discussing using US technology to build conventionally-armed nuclear submarines for South Korea’s Navy.

John Pike, a US military intelligence analyst, believes that Japan will focus for the next several years on building an improved missile shield against North Korea using US technology. But in the long term, he sees the country veering toward a dual key nuclear sharing option such as Matsumura’s.

“This is not a choice but a necessity, given that the country possesses little know-how regarding practical details in possession, security, maintenance, and procedures involving nuclear warheads”

“The trajectory (Matsumura) maps out is about right,” said Pike, who runs the think tank globalsecurity.org.

He says a long-term driver for such US-Japan cooperation is the nuclear threat posed by China — assuming that Beijing continues its current face-off with Tokyo and doesn’t pivot to a more conciliatory stance with Japan. At the same time, he says such nuke-sharing might draw a sharp and possibly bellicose reaction from China.

Pike adds that Prime Minister Shinzo Abe would still have considerable hurdles to climb in making a nuclear-sharing arrangement with the US palatable for the Japanese public. But he says it’s only a matter of time before Abe succeeds in overturning the country’s pacifist scruples.

South Korean angle

South Korea, according to Pike, faces the same strategic calculus when it comes to sharing nuclear weapons with the US.

The US withdrew tactical nuclear devices such as nuclear land mines and missiles from the South after the Cold War ended. But some local legislators and military officials have called for rebasing US nukes in South Korea due to the escalating nuclear threat from Pyongyang.

“President Moon has been driven by the logic of the situation to take a far more hawkish posture than he would like,” Pike said.

Richard Sokolsky, a former US State Department official, said in a December 1 analysis that the chances are increasing that South Korea will embark on an indigenous program to develop nuclear weapons.

“If Washington wants to keep the South Korean nuclear genie in its bottle, the administration may need to draw the ROK more closely into US nuclear planning for the peninsula and elevate the visibility of its own nuclear footprint in and around the country,” Sokolsky wrote in his analysis for 38 North, a respected Johns Hopkins University website dedicated to analysis of North Korea.

Doug Tsuruoka is Editor-at-Large of Asia Times

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