The main policy research arm of the Defense Agency in 1981 studied the possibility of Japan going nuclear but concluded the idea wasn’t feasible in light of the nation’s industrial and technological infrastructure, according to a research report obtained by Kyodo News.

The report was compiled by members of the then National Defense College amid the growing threat of the Soviet Union in the early 1980s.

It said Japan was capable of building simple atomic bombs but would require full and active support from the United States in developing payload-capable vehicles and other equipment for tactical and theater nuclear weapons.

Arming the nation with full-fledged strategic nuclear weapons would be too heavy a burden for the industrial and technological infrastructure, the study said.

The researchers also concluded that engaging in nuclear warfare would be devastating for Japan, projecting that one-fifth of the population would be killed in the event of a war with the Soviet Union, according to the report.

It is already known that Japan on several occasions conducted research on the possibility of developing a nuclear arsenal, but this report focused on the technical possibilities. Most of the research projects reached the conclusion it was more realistic to stay under the nuclear umbrella of the United States.

Regarding the 1981 report, the Defense Agency said, “It was independent research. . . . It was not the official opinion of the Defense Agency and has not been adopted in any policy.”

“At that time, there were discussions in and outside the Defense Agency that nuclear weapons could easily be made and at a low cost,” said a nuclear physics expert who provided research assistance for the report.

“The aim of the report was to show that maintaining an overall system (of nuclear weapons) would be too costly and difficult,” he said on condition of anonymity.

The report, dated July 30, 1981, is titled “On nuclear equipment” and was part of a research project on “The future of Japan’s defense policy.”

It was compiled by a Ground Self-Defense Force officer at the defense college and his research assistants amid growing security concerns after the Soviet Union invaded Afghanistan in the late 1970s.

The defense college has since been renamed the National Institute for Defense Studies.

The research was based on the assumption of a five-stage scenario, beginning with the initial phase of producing and possessing several plutonium atomic bombs, to the final stage of developing intercontinental ballistic missiles and submarine-launched ballistic missiles.

While Japan could achieve the initial stage in about three to five years, the report said, the stages beyond that would require support from the United States in military technology, such as facilities for extracting weapons-grade plutonium and developing nuclear reactors for submarines.

In addition, Japan would need allies to provide nuclear testing grounds, it said. It would also need to ensure a supply of uranium.

“It is impossible to build a technological architecture that would contribute to Japan’s defense strategy,” the report concluded.

It estimated a cost of 2.35 trillion yen for Japan to possess 50 bombers, 100 medium-range missiles and three nuclear submarines. To operate a nuclear arms system would require an additional 9,600 personnel, the report said.

Japan’s basic law on nuclear power states that all research, development and use of nuclear power is limited to peaceful purposes.

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