N. Korea accuses Japan of 'sinister intention' over nuclear-powered submarines

North Korea accused Japan of seeking nuclear-powered submarines as a long-term “stepping stone” toward possessing nuclear weapons. The charge came from Pak Ju-won, an international security analyst whose article appeared in the Korean Central News Agency. North Korea described Japan’s policy discussion as a regional security threat.

The immediate trigger was a statement by Japanese Defense Minister Shinjiro Koizumi late last month. Koizumi said Japan was keeping open the possibility of revising its three nonnuclear principles and acquiring nuclear-powered submarines. He also said Japan should discuss nuclear weapons and nuclear-powered submarines “without taboos.”

Pak interpreted those remarks as an effort to build public support for changing Japan’s key security documents, which were due for revision by the end of the year. He said Japan had abandoned the “veil” of exclusive defense. North Korea argued that the move could worsen military tensions and reshape security competition in the region.

A nuclear-powered submarine uses heat from a nuclear reactor to produce steam and drive turbines. The reactor supplies propulsion and onboard electricity for long periods. It does not automatically make the vessel a nuclear-armed platform. A submarine can be nuclear-powered while carrying conventional torpedoes or missiles.

A nuclear-armed submarine is defined by its weapons, not its engine. It carries nuclear warheads, often on ballistic or cruise missiles, or in some cases uses nuclear weapons delivered by other systems. Its propulsion system may be nuclear or conventional. These two features are separate, even though some countries combine them in the same vessel.

This distinction matters in the Japan debate. Japan’s possible acquisition of nuclear-powered submarines would concern propulsion technology, while North Korea argues that the capability could eventually support nuclear weapons development. That argument is political and strategic; nuclear propulsion alone is not proof that a country possesses nuclear weapons.

Six countries currently operate nuclear-powered submarines: the United States, Russia, the United Kingdom, France, China, and India. Nuclear propulsion gives submarines much greater endurance than conventional diesel-electric systems. They can remain underwater for long periods and travel far without surfacing to recharge batteries or obtain air for engines.

The key mechanism is the reactor’s continuous production of heat and electricity. This supports high underwater speed, extended patrols, and powerful onboard sensors. Nuclear-powered submarines can therefore cover large ocean areas and be harder to detect. Their crews still need food and maintenance, so their missions are not literally unlimited.

These advantages explain why nuclear-powered submarines are associated with major military powers and long-range naval strategy. They can protect sea lanes, track other vessels, and support deterrence missions. However, operating them requires advanced industrial, technical, safety, and regulatory systems. The article discusses Japan’s possible interest but does not state that Japan currently operates such submarines.

Japan’s three nonnuclear principles are that it will not possess nuclear weapons, will not produce them, and will not allow their introduction into Japan. They are a national policy framework rather than the same thing as a nuclear weapon itself. The article says Japan’s defense minister was keeping open the possibility of revising them.

Changing the principles could permit Japan to reconsider one or more of those restrictions. In practical terms, that could open debate about possessing, producing, or allowing nuclear weapons on Japanese territory. It could also change how Japan writes its security documents. Revision would not automatically build a weapon or prove that Japan had decided to do so.

The political significance is why North Korea reacted strongly. Pak Ju-won said Japanese officials were trying to create public support for including nuclear issues in revised security documents. The article does not state that Japan had changed the principles. It reports only that Koizumi said revision and broader debate remained possible.

North Korea argues that nuclear-powered submarines could become a stepping stone toward nuclear weapons because they would normalize nuclear technology in Japan’s defense system. Pak Ju-won described Japan’s alleged long-term intention as formalizing nuclear submarine ownership before moving toward nuclear weapons. The claim is political and reflects North Korea’s stated security concerns.

The mechanism is indirect. Building nuclear-powered submarines requires reactors, specialized engineers, fuel management, industrial facilities, and sensitive technical knowledge. Some of those capabilities can overlap with broader nuclear expertise. The overlap does not mean propulsion technology automatically produces a weapon, but it can reduce political and technical barriers to a future weapons decision.

North Korea also linked the issue to Japan’s possible revision of its nonnuclear principles and security documents. Pak said Japan had abandoned its postwar “exclusive defense” policy. He warned that the alleged plan could create military imbalance and a new structure of fierce regional conflict, bringing disaster to Japan.

In the article, “exclusive defense” refers to Japan’s postwar policy of limiting the use of military force to self-defense. Pak Ju-won said Japan had discarded the “veil” of that policy. His wording presents the change as evidence that Japan is moving away from a strictly defensive security posture.

Since World War II, Japan has maintained constitutional and political limits on military activity, but its security role has gradually expanded. It has developed sophisticated self-defense forces, strengthened its alliance with the United States, and taken on wider regional security responsibilities. These developments do not mean Japan has adopted nuclear weapons or abandoned every restriction on force.

The article focuses on the latest possible step: debating nuclear weapons, nuclear-powered submarines, and revisions to key security documents. North Korea says this direction could upset the regional military balance. The source does not provide a detailed timeline of Japan’s postwar changes, so the broader historical context comes from established background knowledge.

International rules distinguish nuclear naval propulsion from weapons by purpose, materials, and safeguards. A reactor used to propel a submarine is not itself a nuclear weapon. Under the Nuclear Non-Proliferation Treaty, non-nuclear-weapon states may use nuclear energy peacefully, but they must not manufacture or acquire nuclear weapons. Nuclear material and facilities remain subject to safeguards designed to detect diversion.

Naval propulsion creates a special verification challenge because treaty safeguards can allow nuclear material to be placed in a military non-explosive use. A country must arrange procedures with the International Atomic Energy Agency to account for the material and demonstrate that it is not being diverted to weapons. The reactor can power a vessel, but weapon production requires additional steps, including obtaining suitable fissile material and designing an explosive weapon.

The distinction is therefore legal and technical, not absolute in political terms. Nuclear-powered submarines can build expertise and raise proliferation concerns, as North Korea argues. But acquiring propulsion technology does not by itself violate nonproliferation rules or establish a nuclear arsenal.