Extended Nuclear Deterrence Strategy

Through thoughtful and careful design, postwar Japanese security policy has cleverly but not cynically adopted and protected the utility of nuclear deterrence – including reserving Japan’s right ultimately to possess nuclear weapons — while maintaining respect for its postwar Constitution that forever renounces war as a sovereign right and the threat or use of force as a means of settling international disputes.

Japanese Prime Minister Sanae Takaichi is considering revising one of Japan’s longstanding cabinet decisions of not possessing, producing or permitting the introduction of nuclear weapons.[1] Takaichi, it is reported, is eager to bolster Japan’s defense capabilities, including strengthening the extended nuclear deterrence the United States affords Japan. A decision to become a nuclear power may sound cynical, if not unconstitutional. But postwar Japanese security policy has carefully and thoughtfully protected this right, consistent with principles of international law. Becoming a nuclear power is not only possible for Japan, consistent with its Constitution, but maybe even inevitable, as the totalitarian states of the People’s Republic of China and the Democratic People’s Republic of Korea continue to build substantial stockpiles of nuclear weapons and ballistic missiles, placing Japan well in range of hundreds of such weapons.

Though many cite Japan’s alleged aversion to nuclear weapons, having suffered two atomic bombings in 1945, it is important to note that postwar Japanese leadership has never renounced the logic or utility of nuclear weapons or deterrence. In fact, the opposite is more true: Japanese leadership has consistently remained concerned over its vulnerability first to Soviet and now Chinese and North Korean nuclear weapons and their related political influence. It is understandable, then, that the Prime Minister has increasing concerns toward the Chinese and North Korean nuclear programs, as they continue to modernize and expand with no discernable check.

Japan’s Current Policy is Not a Significant Change

Although Japan maintains its extended nuclear deterrent without stationing nuclear weapons inside its territory, Japan maintains a level of nuclear deterrence through a rather Japanese approach. The Treaty of Mutual Cooperation and Security, signed in Washington, DC on January 19, 1960, commits the United States to defend Japan and recognizes the defense of Japan as a matter of common interest. The Treaty also addressed procedural concerns the Japanese developed over U.S. consultations. The United States notifies Japan of upcoming visits of nuclear-powered ships, although not required to do so, and has not attempted to introduce tactical nuclear weapons or nuclear-capable field missiles explicitly into Japan since the new treaty was promulgated.

The 1960 Treaty of Mutual Cooperation and Security and related notes of clarification codified for both the United States and Japan a security arrangement acceptable to both parties. The United States was formally committed to the defense of Japan against external attack. The substantial and continuing American presence in and around the four major Japanese islands gave credibility to this commitment. The Japanese government committed itself to the defense of Japanese territory but did not assume any responsibility outside of Japan. It also had established a consultative arrangement for the arming and deployment of U.S. forces in Japan.

American forward military strategy in East Asia and in the Pacific from the 1950s until 1991 included the presence of theater nuclear weapons first deployed in the Republic of Korea and on American naval ships. U.S. President Richard Nixon, in his 1970 Report to Congress, asserted that “the nuclear capability of our strategic theater nuclear forces serves as a deterrent to full-scale Soviet attack on NATO Europe or Chinese attack on our Asian allies.”[2]

The explicit obligation to maintain a nuclear as well as conventional umbrella for Japan was first undertaken by President Lyndon Johnson in January 1965. During their summit meeting in Washington, President Johnson assured his summit guest, Prime Minister Eisaku Sato, that the United States was determined to abide by its commitment under the 1960 Treaty of Mutual Cooperation and Security to defend Japan against any armed attack from outside.[3] U.S. President George H.W. Bush unilaterally withdrew all tactical nuclear weapons from all U.S. surface ships in 1991. Although his decision may have been driven more by a desire to free surface ship magazines from space-wasting nuclear weapons, and less of a change in deterrence strategy, this posture has continued since 1991. Changing such posture on U.S. surface ships would be costly, involve additional communication capabilities, and re-introduce a series of C3I requirements for such weapons.

Nixon’s Secretary of Defense, Melvin Laird, in 1972, extended the president’s implicit guarantee for the defense of Japan, “coupling” Japan’s conventional defense with the threat of escalation by the United States to the strategic nuclear level:

Our theater nuclear forces add to the deterrence of theater, conventional wars in Europe and Asia; potential opponents cannot be sure that major conventional aggression would not be met with the use of nuclear weapons. The threat of escalation to strategic nuclear war remains a part of successful deterrence at this level.[4]

Potential aggressors had to consider the possibility that regional conventional or nuclear war against Japan would be met with U.S. retaliation, including the use of nuclear weapons. Japan’s security, like Europe’s, was explicitly coupled with the threat of U.S. strategic war as national policy. Deterrence was formally “extended” to Japan and Western Europe by the United States.

Article IX of the postwar Japanese Constitution states,

…the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes… land, sea, and air forces, as well as other war potential, will never be maintained. The right of belligerency of the state will not be recognized…

There is No Right of War

But soon after the Constitution was adopted, the Japanese Supreme Court ruled that the article does not prohibit Japan from maintaining military forces for the purposes of self-defense. And since any weapon can be deemed defensive, it is important to note that no Japanese government has ever declared the possession of nuclear weapons unconstitutional.

Although he had stated previously Japan had no intention of possessing nuclear weapons, in 1958, in the House of Councilors, Prime Minister Kishi declared, “Depending on future developments in nuclear weaponry, I do not think that the Constitution bans nuclear weapons if they are of a defensive character…”[5] In 1959, Kishi declared as legal the possession of “the minimum amount of nuclear weapons for the purpose of self-defense.”[6]

The first postwar White Paper on Defense, published under the Minister of State for Defense, Yasuhiro Nakasone, in 1970, reaffirmed Kishi’s statement: “… if small-size nuclear weapons are within the scale of real power needed for the minimum necessary limit for self-defense, and if they are such as will not be a threat of aggression toward other nations, it is possible to say that possession thereof is possible, in legal theory.”[7]

In 1970, Masami Takatsuji, director of the Cabinet Legislation Bureau, extended the scope of defensive capabilities to include “defensive nuclear weapons.” When Prime Minister Sato was questioned about Takatsuji’s suggestion that nuclear weapons could be considered defensive weapons, Sato stated that he found nothing in Takatsuji’s statement that he needed to correct.

During a Mainichi Shimbun interview, on May 9, 1981, former U.S. Ambassador to Japan, Edwin O. Reischauer, revealed that he was informed an oral agreement had been reached during the U.S.-Japan security treaty negotiations of 1960, defining “introduction” of nuclear weapons as “putting them ashore and storing them.” It was Reischauer’s understanding that this agreement did not prevent the United States from moving the weapons through Japanese straits or into Japanese waters as long as they were not unloaded ashore.[8] His interview seemed to confirm a New York Times article of October 27, 1974, which reported on a 1960 United States-Japan agreement “permitting U.S. warships to carry nuclear weapons into Japan during port calls and American aircraft to bring them during landing.”[9]

Under customary international law, warships have been entitled to those privileges the right of sovereign immunity accords them. Sovereign immunity is the legal principle which ensures that the subjects and property of one sovereign power are treated on the basis of complete equality by another sovereign power and are therefore immune to search, seizure, interference or any other type of enforcement jurisdiction. The applicable law regulating the internal discipline of a warship’s crew, as well as its design characteristics and equipment, are all regulated by the flag state of the warship.

The 1982 Law of the Sea Convention, in fact, codifies these legal rights. Article 94 protects the rights of ships and reads:

. . . (E)very State shall . . . assume jurisdiction under its internal law over each ship flying its flag and its master, officers and crew in respect of administrative, technical and social matters concerning the ship.[10]

As an extension of the rights guaranteed by the doctrine of sovereign immunity, and consistent with this customary international law, U.S. government policy neither confirms nor denies (‘NCND’) the presence or absence of nuclear weapons at any general or specific location — including aboard any particular warship. Presumably, the introduction issue was purposefully or accidentally left ambiguous in Japan to allow the United States to maintain its neither confirm nor deny policy while remaining sensitive to antinuclear sentiment in Japan.

Foreign Minister Shintaro Abe testified before the House of Representatives Budget Committee on February 23, 1983, that U.S. ships carrying nuclear weapons would constitute “introduction” into Japan and the issue would therefore be subject to prior consultation between the two governments and would not be approved by Tokyo. The United States, for its part, understands and respects the three nonnuclear principles but does not confirm or deny the presence or absence of nuclear weapons at any general or specific location.

Japan’s Nonconfrontational Approach Enables Its Nuclear Deterrence Policy

Since the United States repeatedly assures Japan that it has abided and will abide by the commitments it assumed under the Treaty of Mutual Cooperation and Security and by the prior consultation agreements, Japan is publicly satisfied that since Washington has not invoked the prior consultation provision, the United States has not introduced nuclear weapons into Japan.

This clever, carefully constructed arrangement can continue, without Japan explicitly renouncing its third non-nuclear principle of not allowing the introduction of nuclear weapons onto its territory and is consistent with international law. The Japanese government purposefully maintains this public ambiguity between formal statements and underlying truth.

Hiromi Kurisu, Chairman of the Joint Staff Council of the Self-Defense Forces from October 1977 to July 1978, called for revision of the non-introduction principle to allow nuclear-capable ships and aircraft to utilize Japanese facilities during military operations in support of U.S.-Japan mutual interests.[11]

While he was Director General of the Defense Agency, Yasuhiro Nakasone, in 1970, argued against nuclear weapons in Japan on the grounds that they would undermine the popular consensus in support of the three nonnuclear principles while contributing little, if anything, to deterrence.[12] Nuclear weapons in Japan would not add appreciably to the deterrence of conflict but might only serve to undermine crisis stability by deploying vulnerable Japanese weapons easily targeted for preemption.

The U.S. extended nuclear deterrent for Japan consists of U.S. central strategic systems and air and sea-based theater systems but no land-based missiles inside Japanese territory. Japanese soil has escaped the import of nuclear weapons. Further, unlike the European allies, Japan is not involved in joint planning with the United States over the deployment and employment of nuclear weapons in its theater. There is no Nuclear Planning Group for the U.S.-Japan alliance to discuss joint nuclear strategy. Japanese and American officials may meet in various joint defense planning committees to discuss the role of nuclear weapons for the security of Japan[13] but they have no analogous forum to the NATO Nuclear Planning Group. In addition, unlike the European allies, Japan is not involved in the development of operational guidelines over the use of nuclear weapons should deterrence fail. The Japanese approach is one of total reliance on American strategy.

In contrast with NATO allies, in the April 2023 Washington Declaration, the United States merely pledged to make “every effort to consult” with the Republic of Korea on any possible nuclear weapons employment.[14] And, in a quick follow-up, the August 2023 Camp David Trilateral Pact, among the United States, the Republic of Korea, and Japan, commits the United States merely to consult its East Asian allies over defense issues.

In contrast to Europe, the United States need not consult with Japan before using nuclear weapons in a conflict around Japan. NATO contains a multi-lateral framework to (ostensibly) discuss use of nuclear weapons for NATO’s defense. The U.S.-Japan alliance has no such consultation procedure beyond the prior consultation notes which apply only to the introduction of nuclear weapons into Japan.

Since Japan enjoys a geostrategic environment different from the more land-oriented European theater, Tokyo has been able to maintain the American nuclear guarantee at sea and in the United States. Extended nuclear deterrence for Japan has not required the stationing of land-based missiles inside Japan. In fact, the United States may maintain greater crisis stability by keeping them offshore and at sea and essentially invulnerable to attack. The U.S. nuclear guarantee is made credible by its strong declaratory policy to defend Japan from attack, its commitment to survivable central strategic nuclear systems and its conventional theater options on Guam, on aircraft carriers, on submarines and on surface ships. Deterrence does not necessarily require the presence of nuclear weapons inside Japan; nor do Japan’s three nonnuclear principles threaten the credibility of the U.S. extended nuclear guarantee to Japan.

Since the 1991 withdrawal of U.S. nuclear weapons from U.S. surface ships, the United States has reaffirmed its policy of no nuclear weapons on surface ships in DoD statements and in Congressional testimony on the implementation of the 1991 Presidential Nuclear Initiative (PNI). The United States later reaffirmed such a posture in the 2010, 2018, and 2022 Nuclear Posture Reviews (NPR), noting that all tactical naval nuclear weapons had been removed and retired and that the U.S. Navy only deploys nuclear weapons of any kind on SSBNs.[15]

In the 2022 Nuclear Posture Review, the United States pledged to cancel the nuclear-armed Sea-Launched Cruise Missile (SLCM-N) program.

“The 2018 NPR introduced SLCM-N and the W76-2 to supplement the existing nuclear program of record in order to strengthen deterrence of limited nuclear use in a regional conflict. We … concluded that the W76-2 currently provides an important means to deter limited nuclear use … (and that the) SLCM-N was no longer necessary given the deterrence contribution of the W76-2, uncertainty regarding whether SLCM-N on its own would provide leverage to negotiate arms control limits on Russia’s NSNW, and the estimated cost of SLCM-N…”[16] [17]

But more recently, U.S. lawmakers have debated the merits of a proposed “nuclear-armed sea-launched cruise missile (SLCM-N),” a weapon that was first proposed during the first Trump Administration. “A United States Navy official told lawmakers that the SLCM-N would be one of the service’s top three warfighting priorities. The missile could be launched from the service’s Virginia-class fast attack submarines (SSNs).”[18] If approved, the SLCM-N would be the first such nuclear weapon deployed on U.S. SSNs since the end of the Cold War. Should the SLCM-N be deployed, the ‘NCND’ policy would become more relevant internationally but, until then, the United States will likely not amend its current posture that the surface fleet is free of nuclear weapons.

Japan’s Nuclear Weapons Policy is Evolutionary, Not Revolutionary

Prime Minister Takaichi’s statement that Japan might allow the introduction of nuclear weapons involves little change to U.S. or Japanese military posture. U.S. SSBNs do not visit Japanese ports. And although U.S. policy will continue to defend its ‘NCND’ policy regarding its surface fleet, grounded in international customary law, U.S. surface vessels are unlikely to include tactical nuclear weapons anytime soon. Japan’s clever acceptance of U.S. NCND policy will likely continue, therefore, without precipitating much internal Japanese friction. Therefore, Takaichi’s statement likely changes little currently and involves no change in U.S. or Japanese military posture for the immediate future. It is more of a public affirmation of U.S. extended nuclear weapons policy but lays the intellectual groundwork for stationing U.S. nuclear weapons on Japanese territory sometime in the more distant future, should the situation in East Asia worsen.

While adhering to three nonnuclear principles and calling for nuclear disarmament, Japan has not renounced the utility of nuclear deterrence. Neither has Japan renounced a right to build Japanese nuclear forces. Japan sought an extended nuclear deterrent from the United States and supports U.S. global and theater nuclear strategy. The objective, as in Europe, is to prevent war, deter conventional and nuclear attack and check Chinese and North Korean political-military intimidation. Currently, Japan keeps the U.S. deterrent offshore and relies on U.S. strategy while approving of the presence of U.S. nuclear-capable assets in the region.

Japan’s Rather Japanese Nuclear Strategy

Through clever design, Japanese “nuclear strategy” includes the following:

1. Maintain the three nonnuclear principles of Japan, call for nuclear disarmament, but note the worsening situation surrounding Japan.
2. Maintain the U.S. extended nuclear guarantee and support the presence of U.S. nuclear assets in the region (but keep them offshore currently).
3. Maintain the credibility of the U.S. nuclear guarantee through defense cooperation, support of U.S. theater strategy, host nation support, coordinated conventional defense planning, an American serviceman presence and political-economic interdependence.
4. Construct a useful ambiguity over the introduction of nuclear weapons ‘into’ Japan and do not press the United States over this issue.
5. Build capable conventional defenses to raise the nuclear and conventional threshold.
6. Preserve the legal and intellectual option in Japan for development of “defensive nuclear weapons”.
7. Maintain the nuclear fuel, engineering, and technical capability to build nuclear weapons and mate them to a version of their three-stage space launch vehicles.

Even though Japan does not explicitly associate itself with U.S. nuclear strategy, it does accept the utility of deterrence and does not want to see its security separated from the American nuclear umbrella. Japanese “existential deterrence” and conventional defense rest on maintaining a close strategic relationship with the United States and on a continuing commitment from Washington to the East Asian region.

Japan’s strategy is carefully constructed, consistent with international principles of self-defense, moving in concert with the evolving attitudes of the Japanese people, and sadly likely to be perceived by the Japanese people as inevitable and just, given the increasing nuclear belligerence of the PRC and DPRK. Japan going nuclear may be the inevitable future of the United States’ inability to restrain the never-ending truculence of the now totalitarian states of China and North Korea, both of which have decided unambiguously to become global nuclear powers.