In an article to the Hudson Institute shortly before his election as LDP president, the new Prime Minister Ishiba wrote the following; “Recently, Russia and North Korea have formed a military alliance, and nuclear technology is being transferred from Russia to North Korea. North Korea is strengthening its nuclear and missile capabilities, and if China’s strategic nuclear weapons are added to these dynamics, the U.S. extended deterrence in the region will no longer function. This is to be supplemented by an Asian version of NATO, which must ensure deterrence against the nuclear alliance of China, Russia, and North Korea. The Asian version of NATO must also specifically consider America’s sharing of nuclear weapons or the introduction of nuclear weapons into the region.¹”

In addition, on September 16, 2024, in an online debate of candidates for the LDP presidential election, he made the following statement in relation to nuclear sharing; “When you talk about nuclear sharing, people say, 'Oh, Japan is going to have nuclear weapons,' but that is not true. We won't have the right to own or control nuclear weapons. But if we don't have close coordination on when to use and when not to use nuclear weapons, the nuclear umbrella may not be extended to us when the time comes. It may be tiny. It may have a hole. It's not just a matter of believing in it, but nuclear sharing means sharing the decision-making process, so it's not something that basically violates the three non-nuclear principles, either².”

In light of the above, Mr. Ishiba, in discussing the issue of "nuclear sharing and nuclear introduction," argued that (1) as a result of the current activities of China, North Korea, and Russia, U.S. extended deterrence will no longer function, (2) it is therefore necessary to establish an Asian version of NATO, where deterrence against the nuclear alliance of China, North Korea, and Russia is secured, and for this purpose, “nuclear sharing and nuclear introduction” by the U.S. should also be considered. (3) “Nuclear sharing,” however, means sharing the decision-making process, and basically does not violate Japan's three non-nuclear principles.

Based on this, the following six points should be kept in mind when discussing the future "nuclear sharing and nuclear introduction.”

In his writing of the Hudson Institute, Mr. Ishiba notes that "the U.S. extended deterrence in the region will no longer function," but it is necessary to be aware of the time frame for this claim. If he means that the credibility of the U.S. extended nuclear deterrence will be called into question by the buildup of nuclear capabilities of China, North Korea, and Russia, this is not an immediate problem, but a medium and long-term issue that will become apparent after about 2035.

This is because, even if China is rapidly expanding its nuclear arsenal, it is not expected until after 2035 that China's nuclear warheads will match the number of U.S. deployed strategic nuclear warheads (estimated at about 1,770 in 2024; the U.S. Department of Defense estimates that by 2035 China will have 1,500 warheads). And even at that point, it is not clear whether China will rival the U.S. in the total number of deployed and non-deployed strategic nuclear warheads in stockpile (the total number of deployed and non-deployed U.S. nuclear warheads in 2024 will exceed 3,700³). Of course, if China approaches the U.S. in the number of nuclear warheads, deterrence failure in the region will become more likely under the so-called the "stability-instability paradox,⁴” so there is no doubt that Japan needs to take serious action, but this is not a problem that is immediately at hand.

Nevertheless, there is certainly a need to begin efforts at this time to address the problems that will emerge after 2035. In fact, the U.S. also faces the need to simultaneously deter both China and Russia as a result of China's nuclear arms buildup, and in October 2023, a bipartisan congressional commission published its recommendations on future strategic posture⁵. It contains a number of recommendations, including that the U.S. should "upload" non-deployed nuclear warheads to existing nuclear force platforms to ensure that the U.S. has a sufficient number of deployed strategic nuclear warheads. If Japan were to need to engage in the "nuclear sharing" or "nuclear introduction" initiatives in the future, it would take many years to prepare for such initiatives, so it is worthwhile for Japan to discuss and have a vision for such initiatives at this point.

In essence, however, it is necessary to be aware that these initiatives are not something that is feasible in the immediate future but is a medium and long-term issue that will be addressed in 2035 and beyond.

Mr. Ishiba claimed that "The Asian version of NATO must also specifically consider America’s sharing of nuclear weapons or the introduction of nuclear weapons into the region.” In this regard, it is necessary to sort out the vision of whether the "nuclear sharing and nuclear introduction" initiatives should be implemented bilaterally between Japan and the U.S. or within some kind of multilateral framework. At this point, the specific image of an "Asian version of NATO," as pointed out by Mr. Ishiba, is not clear, and there is debate over its feasibility and whether it is a collective defense organization or a collective security organization in the first place. There is also a persistent argument that such a multilateral framework is not feasible given the diversity of nations in the Indo-Pacific region. Nevertheless, the idea of some kind of multilateral framework for "nuclear sharing and nuclear introduction" in the Indo-Pacific region is not entirely without reality. This is because the U.S. does not consider deterrence against China in the region on a bilateral basis, but rather on a "horizontal" basis, based on cooperation with multiple regional nations. In the future, there will be some possibility of multilateral discussions over the issue of the credibility of the U.S. extended nuclear deterrence, for example, that would involve the Japan-U.S. alliance and the U.S.-Australia alliance, the U.S.-ROK alliance, and so on, on a horizontal basis.

Even in such a case, however, we cannot ignore the fact that each nation has its own political situation and threat perception. For example, between Japan and South Korea, which share the threat of North Korea, there will continue to be a gap in perception as to how far China is considered to be the main axis of threat. Even among Japan and Australia, the geographical distance from China is different, so there must be differences in the "ideal form" of extended nuclear deterrence. It would be difficult to discuss multilateral extended deterrence with a nation outside of that, such as India, which has its own nuclear arsenal and emphasizes "strategic autonomy.” In other words, even if it is possible to have a common multilateral understanding (among a limited number of nations) about maintaining the credibility of the U.S. extended nuclear deterrence in the broadest sense, the actual "nuclear sharing" or "nuclear introduction" would be premised on a bilateral basis between the U.S. and each nation.

In the case of Japan, of course, it is inevitable to consider how to change the "three non-nuclear principles" in order to realize the "nuclear introduction," what form the "nuclear introduction" should take, and if it goes as far as "nuclear sharing," what kind of force platform should be used for "sharing" and how the decision-making process should look like when operating the nuclear weapons (these points are discussed below). Consequently, it is also essential to independently verify whether these measures would be the best way for Japan to maintain the credibility of extended nuclear deterrence. These issues would need to be determined on a bilateral basis.

Mr. Ishiba stated, "Nuclear sharing means sharing the decision-making process, so it's not something that basically violates the three non-nuclear principles, either." But this does not necessarily seem to be the general interpretation of "nuclear sharing.” The "nuclear sharing" generally interpreted is the "NATO-style nuclear sharing," which Yoko Iwama defines as follows; “the institution that the U.S. stores the nuclear weapons on ally’s territory, the allies possess the means of delivery with which they plans to operate the nuclear weapons in the event of war, and in the event of war and when a decision to use the nuclear weapons in NATO was once made, the U.S. supplies the nuclear weapons to the allies, which then places the nuclear weapons on its own means of delivery for use⁶."

At present, the U.S. is believed to have forward-deployed a total of about 100 non-strategic nuclear warheads (B-61 nuclear bombs) to five NATO allies, and allies that accept these warheads operate the U.S. non-strategic nuclear warheads using the Dual Capable Aircrafts (DCA), which can be used for both nuclear and conventional weapons⁷. The consent of both the U.S. and the allies is required to operate the system, which is called a “dual key” system. In other words, as long as "NATO-style nuclear sharing" is considered, it is essential for allies to accept the "introduction" of U.S. nuclear weapons into their territories. And the platform for the allies to operate U.S. nuclear weapons is the DCA (specifically, various fighter aircrafts of each country, such as the F-15E, F-16, and PA-200 Tornado, which all will be upgraded to F-35A fighters in the near future).

It should be noted, however, that NATO has a separate consultative framework, the Nuclear Planning Group (NPG), which is a permanent consultative body and includes all member states except France, and is a mechanism for information sharing and consultation on a broad range of nuclear policy matters, including the overall effectiveness of NATO's nuclear deterrent, the safety, security and survivability of nuclear weapons, and communications and information systems⁸. It is a forum in which member states can participate in the development of alliance nuclear policy and decisions regarding NATO's nuclear posture, regardless of whether they themselves accepts the U.S. nuclear weapons on their territories. This is sometimes regarded as "software-based" nuclear sharing as opposed to "hardware-based" nuclear sharing⁹. Mr. Ishiba's claim that "nuclear sharing means sharing the decision-making process" may be based on this recognition of the NPG.

In other words, even if we speak of "nuclear sharing" in one word, the discussion may be confusing unless we clarify what it means in concrete terms. First of all, it must be clarified whether the term "nuclear sharing" refers to the "hardware-based" “NATO-style nuclear sharing” or the "software-based" nuclear consultations alone. In the former case, the "nuclear introduction" as an ally is indispensable, but if limited to the latter case, there is room for understanding that, as Mr. Ishiba says, "it's not something that basically violates the three non-nuclear principles.” And if we take the latter position, since the Japan-U.S. Extended Deterrence Dialogue (EDD) have already been held since 2010, and as recently as July 28, 2024, a Japan-U.S. Ministerial Meeting on Extended Deterrence was held with a higher rank of participants¹⁰, it will be essential to clarify what is lacking in the existing consultation efforts and what needs to be newly initiated.

Furthermore, even if the "hardware-based" nuclear sharing is adopted, there is a good possibility that a form of nuclear sharing different from "NATO-style nuclear sharing" will be pursued, considering the characteristics of Japan and the Indo-Pacific theater. As will be discussed in detail in the next section, it is highly possible that nuclear sharing by the DCA is not the optimal form for the Indo-Pacific theater. If this is the case, it will be necessary to discuss the possible forms of "nuclear sharing" between Japan and the U.S. in concrete terms, and why this is the best form to enhance the credibility of deterrence and to provide reassurance to allies, based on a concrete image.

To further explore the above topic, a "NATO-style nuclear sharing" centered on the DCA is unlikely to be the optimal form for the Indo-Pacific theater. This is because it is easy to assume that the DCA’s short-range capability and the use of free-fall B-61 nuclear bombs would face operational challenges if the main objective is to deter China. As is well known, China has been developing its so-called "Anti-Access/Area Denial (A2/AD)" capabilities over a long period of time in anticipation of an invasion of Taiwan. In light of this, even if we assume the F-35A stealth fighter as the DCA, its short-range capability (combat radius of about 1,240 km) makes it difficult for it to cross the Pacific and East China Sea and strike with sufficient strategic depth. In any case, it would have to be deployed to forward air bases, which would likely be subject to dense attack by China's A2/AD capabilities, thus limiting its operational capability. Even if aerial refueling aircraft are used to extend the combat radius of fighters, the survivability of these refueling aircraft (basically, non-stealth) becomes a next issue.

Therefore, whether "nuclear sharing" or "nuclear introduction" is seriously considered in the Indo-Pacific theater, it will be necessary to explore other options besides the combination of DCA and B-61 nuclear bombs. As already mentioned, if we look at this as a medium and long-term issue and assume that the U.S. nuclear capability is expected to be available around 2035, the following options for "nuclear sharing" or "nuclear introduction" in the "Indo-Pacific-style" would be possible.

One is the use of existing Trident SLBMs (submarine-launched ballistic missiles) with low-yield nuclear warheads. A Trident SLBM tipped by the single warhead (W-76 mod2) with a nuclear power of 8 kt has already been deployed during the Trump administration. The "port call" of Ohio-class/Columbia-class strategic nuclear submarines (SSBNs) that operate these missiles to allied nations can be envisioned as an option for the "introduction" of nuclear weapons. In fact, the port call of the SSBN "Kentucky" to Busan, South Korea, has already been realized on July 18, 2023, and this is a feasible "nuclear introduction" option that is currently available. However, SSBNs/SLBMs are essentially a means to project strategic nuclear warheads at long-range, and since SSBNs have strategic significance in terms of their survivability, their location should be kept absolutely confidential. Moreover, SLBMs should be launched from sufficiently remote locations considering their long-range capability, and if SLBMs are forward-deployed in a form of such as port call to allied nation, they will be forced to launch missiles in so-called "lofted" or "depressed” trajectory, which gives a strong impression that it is difficult to find any military meaning in such a situation. Furthermore, projecting nuclear weapons using SLBMs, even with low-yield warheads, could be misunderstood as a strategic nuclear attack, and the fear of inadvertent escalation cannot be denied. Therefore, it must be pointed out that even though the port call to an allied nation by an SSBN carrying an SLBM with a low-yield nuclear warhead may have some political/psychological impact, from a military perspective, it is highly problematic. Furthermore, it should be noted that SLBMs with W-76 mod2 are limited in number¹¹ and the nature of SSBNs operating strategic nuclear warheads could make them a "nuclear introduction" option, but not a "nuclear sharing" option.

The next option is to deploy the long-range strategic bombers (B-21/B-2/B-52H) to allied nations carrying the new air-launched cruise missiles (LRSO: Long-Range Stand Off weapon) with nuclear warheads. The strategic bombers carrying cruise missiles have the obvious advantages over DCA/B-61 nuclear bomb option: they can conduct longer-range/standoff attacks from remote locations. And there is also a notable advantage to bomber deployment that is not present in the use of submarines such as SSBNs. That is, the forward deployment of nuclear bombers can be visibly demonstrated to the adversary, and even if the bombers start to fly, they can be recalled before the missiles are launched, which is operationally flexible. On the other hand, there is an obvious disadvantage to the combination of strategic bombers and LRSO. This option clearly is less "survivable" than the operation of nuclear weapons from submarines. No matter how long the range of the bombers and missiles may be, as long as it is the “introduction” of nuclear weapons, they must be forward deployed to allied nations, and the risk of a Chinese attack on air bases and related facilities cannot be eliminated. In addition, it cannot be denied that the U.S. has a variety of options in the Indo-Pacific theater other than "nuclear introduction." There is the option of introducing nuclear weapons to Guam or flying the bombers from Alaska or the U.S. mainland and operating them on the high seas. There is no denying that forward deployment to allied nations could make the bombers and nuclear weapons vulnerable. Still, having multiple deployment sites in the region would be a dispersal advantage for U.S. bombers to mitigate damage from Chinese A2/AD attacks, but the additional military utility of deterrence by "nuclear introduction" is expected to be marginal. And since Japan's interpretation of its Constitution prohibits the possession of long-range strategic bombers by positioning them as beyond “the minimum necessary level of self-defense capability¹²,” this, too, cannot be an option for "nuclear sharing" without a change in the interpretation of the Constitution.

The third option concerns a sea-launched cruise missile with a nuclear warhead (SLCM-N), which was originally conceived for development during the Trump administration but was cancelled by the Biden administration. The SLCM-N was originally conceived as a successor to the TLAM-N, a submarine-launched Tomahawk cruise missile with a nuclear warhead, which was decided to retire during the Obama administration. But the development of SLCM-N was canceled after it was deemed unnecessary under the Nuclear Posture Review (NPR 2022) of the Biden administration. Afterward, though the Administration did not request a budget for the program, Congress continued to fund it, and as a result, the FY2024 National Defense Authorization Act mandated that the Administration to establish a program for the development of SLCM-N (Section 1640).¹³
The SLCM-N has been attracting attention in recent years as an alternative "nuclear sharing" and "nuclear introduction" option to the SSBN/SLBM and strategic bomber/LRSO combinations described above, and is expected to be operated by Virginia-class attack submarines (SSN), if realized, which would allow the U.S. to operate nuclear weapons within the theater while taking advantage of the high "survivability" characteristic of submarines. In addition, the U.S. has removed all nuclear weapons from surface vessels since 1991, and with the retirement of the TLAM-N, as mentioned above, nuclear operations on submarines other than SSBNs have also ceased¹⁴. The introduction of the SLCM-N will again allow naval vessels other than SSBNs equipped with nuclear weapons to make "port call" to the allied nations.

Moreover, since SSN/SLCM-N is positioned differently from SSBN/SLBM, which operate strategic nuclear weapons, the possibility of inadvertent nuclear escalation is relatively low. Furthermore, since an adversary would hesitate to attack an SSN that may carry nuclear weapons for fear of the risk of nuclear escalation, the SLCM-N is expected to have the effect of constraining the adversary's anti-submarine warfare (ASW). The use of SLCM-N has obvious advantages, but on the other hand, compared to the use of strategic bombers, submarines have the disadvantage that their location is not clear and it is difficult to determine from the outside whether they are really carrying nuclear weapons, making it difficult to deter them in a "visible" manner. In this sense, the military utility of "nuclear introduction" to an allied nation may be more marginal than in the case of strategic bombers (on the other hand, the ability to "port call" may be meaningful from the perspective of resupply and rest). In any case, the SSN/SLCM-N combination is highly valued from a "survivability" perspective, but has a tradeoff that is inferior to the strategic bomber in terms of whether it is a "visible" means of deterrence to an adversary. It should be noted that the possibility of not only "introducing" the SLCM-N to an allied nation, but also "nuclear sharing" to operate it from an allied submarine would not necessarily be technically ruled out¹⁵.

The above three are the leading options in terms of deterrence measures other than DCA/B-61 nuclear bombs that the U.S. could use around 2035, but if we include those that have no development plan at this time, the option of forward deployment of ground-based medium-range missiles (including cruise/ballistic/hypersonic missiles) with nuclear warheads is also logically possible. Such missiles (with a range of 500-5,500 km) were once known as Intermediate-range Nuclear Forces (INF) and prohibited by the INF treaty from being possessed by the U.S./USSR, but this treaty expired in 2019 due to the violations on the Russian side. Since then, the U.S. has developed the ground-launched medium-range missiles such as the "Typhon" and "Dark Eagle" as a means of countering China's large number of missiles in the same category (DF-21/DF-26, etc.), and some of which are being "introduced" to allied nation in the theater¹⁶. Currently, the U.S.’s ground-launched medium-range missiles are essentially designed to carry conventional warheads only, with no nuclear warheads planned. However, the possibility of their development in the future is not zero, and if such an option emerges, it is not impossible that it could become a means of "nuclear introduction" into the allied nation. Generally speaking, ground-launched missiles have a certain level of "survivability" if they are maneuverable, and they also have excellent "responsiveness" capabilities. In reality, however, “nuclear sharing” (in the sense that the U.S. manages nuclear weapons during peacetime and provides them to its allies in wartime) would be difficult because it is desirable to have nuclear warheads on board missiles at all times from the standpoint of emphasizing responsiveness, and the question of whether this would be a means of "nuclear introduction" by the U.S. would be of interest.

The table below summarizes the above discussion. Simply put, the DCA/B-61 nuclear bomb combination is unlikely to be the optimal form for the Indo-Pacific theater as a means of “nuclear sharing and nuclear introduction.” The combination of SSBNs and SLBMs with low-yield warheads has the advantage of being an immediate means of "nuclear introduction” into the theater, but it has operational difficulties, such as forward deployment of SSBNs and their positional exposure. The strategic bomber/LRSO combination is effective as a “visible” and “flexible” deterrent for adversaries, but has “survivability” problem in being attacked forward deployed air bases and related facilities. The SSN/SLCM-N combination has significant “survivability” advantages due to the nature of the submarine, but has difficulties as a “visible” deterrent measure. And, while ground-launched medium-range missiles, if maneuverable, would be superior in terms of "survivability" and "responsiveness," the U.S. has no development plans for them at this time. If the Japan and the U.S. were to consider "nuclear sharing and nuclear introduction" in the future, it is highly likely that they would adopt a combination of the best means among the above options.

From the standpoint of those who seek to realize "nuclear sharing and nuclear introduction," it may be obvious why they are needed, but in fact it is not necessarily so. This is because, in any case, "nuclear sharing and nuclear introduction" does not go beyond the basic framework of extended nuclear deterrence, and in any of the forms already mentioned, the positive deterrent effect in a purely military sense is considered to be marginal.

This is because, unlike Europe, which has a vast ground-based theater, in the Indo-Pacific theater, which is primarily comprised of sea and air, there is room for the U.S. to provide extended deterrence to its allies by deploying its nuclear forces on and over the high seas without "introducing" them into the allied territories. It is true that deploying nuclear forces to the air bases and ports of allied nations can increase the benefits of dispersion and providing resupply and rest, but compared to the European theater, the benefits of "introducing" the nuclear forces to allied nations in the Indo-Pacific theater are relatively low. From the U.S. perspective, the U.S. may not want to do this because of the risk of increasing vulnerability by forward deployment or of political backlash within the allied nations.

In addition, it is questionable whether "nuclear sharing" really enhances deterrence in a military sense. This is the same story for "NATO-style nuclear sharing," and "nuclear sharing" does not go one step beyond the basic framework of extended deterrence. Even if nuclear weapons are "introduced" into an allied territory, the U.S. is consistently responsible for their control during peacetime. In the event of war, nuclear weapons are supplied to allied nations, but the U.S. and the allies will use them under a "dual key" system. In other words, the U.S. has always the right of veto on the use of nuclear weapons, and unless the U.S. permits their use, allies cannot use them even if they request it. If the "nuclear sharing" initiative is based on doubts about the credibility of the U.S. extended nuclear deterrence, then even if nuclear weapons are "shared," it is essential to obtain the U.S. consent before using them. In other words, confidence in the credibility of U.S. extended nuclear deterrence is the basic premise, and the "nuclear sharing" initiative will not change this basic framework.

So why are there calls for "nuclear sharing and nuclear introduction"? Ultimately, it is because these efforts are more about providing reassurance to allies than about enhancing deterrence. The difference in perception between the U.S. and its allies regarding the credibility of extended deterrence was once pointed out by Denis Healey, the former British defense minister, in his "Healey's theorem,” which was “it takes only 5% credibility of American retaliation to deter the Russians, but 95% to reassure the Europeans¹⁷.” This is a phrase that reflects the fact that the issue of credibility of extended deterrence may not be a major problem for the U.S., but it is a matter of life and death for its allies. Allies are far more sensitive to the shaky credibility of extended deterrence than the U.S., since the life or death of a nation depends on it. The level of credibility required for deterrence may be slight, but the level of credibility required for reassurance sought by allies tends to be much higher.

Because of this difference in perception between the U.S. and its allies, if an allied nation feels unconfident on the credibility of the U.S. extended nuclear deterrence, it has an incentive to demand that the U.S. take some explicit steps to correct this situation. This may not contribute much to actual deterrence, or it may be little more than a symbolic effort, but allies will still demand that the U.S. take some concrete steps to provide reassurance to allies in some definite way. And if such efforts are not made, the allies will continue to feel insecure. In the end, this may encourage nuclear proliferation to allies. To prevent such a development, the U.S. has an incentive to implement "nuclear sharing and nuclear introduction" measures to provide reassurance to allies.

NATO's "nuclear sharing" typically followed this path. After adopting an idea of "massive retaliation" as its nuclear deterrence strategy in the 1950s, in the 1960s the U.S. shifted it to a strategy of "flexible response" that emphasized the role of conventional forces more. The European allies felt unconfident on this change. The European allies feared that the reduced role of nuclear weapons in the U.S. deterrence strategy would jeopardize their ability to deter the Soviet Union. The U.S. feared that this concern about the credibility of U.S. extended nuclear deterrence would lead to nuclear proliferation to its allies. As a result, the U.S. tried to alleviate the concerns of its allies by even coming up with such eccentric concepts as the multilateral operation of strategic nuclear weapons by NATO units (the MLF concept), but in the end, after some twists and turns, it settled on the "NATO-style nuclear sharing" and the establishment of a consultative framework called the NPG, as already mentioned. From the perspective of the allies, the "nuclear sharing" was part of the reassurance provided by the U.S. in exchange for their pledge not to arm themselves with nuclear weapons.

Of course, the fact that a theoretical distinction should be made between deterrence and reassurance does not mean that there is no connection between the two. Measures that do not contribute to deterrence in any way may not be reassurance-providing in the first place. Nevertheless, it is necessary to understand that "nuclear sharing and nuclear introduction" may not necessarily mean a high deterrent effect from a military perspective. Rather, it has the political and psychological effect that should be expected. When an allied nation takes these kind of initiatives despite strong domestic opposition, the challenging nation sees in it a strong commitment to deterrence by the allied nation and the solidarity between the U.S. and its allies. The idea of "nuclear sharing and nuclear introduction" should primarily be evaluated for these non-military deterrent effects.

The idea of “nuclear sharing and nuclear introduction" is technically feasible for Japan if a political decision is made. However, it is necessary to carefully examine the additional issues involved.

For example, to achieve " nuclear introduction," it would naturally be necessary to amend the "three non-nuclear principles” of Japan. Although this is a Diet resolution, not a law, there will be a difference between whether the amendment is likewise made by a Diet resolution or as a political decision by the government at the time¹⁸. In any case, proper fulfillment of accountability to the public cannot be lacking.

Furthermore, the reactions of local governments and residents in the vicinity of the "nuclear introduced" location will not be ignored. Various efforts to persuade the local governments and residents to accept the program will undoubtedly be necessary. It is also essential to respond to accidents and local concerns that the area will be vulnerable to attacks. It must be assumed in advance that such efforts will take a considerable amount of time. Consultations with the U.S. on how to operate "introduced" nuclear weapons is also necessary. The existing nuclear talks must undoubtedly be further enhanced. In addition, if nuclear weapons are to be "stored" or "stockpiled" in Japan on a permanent basis, rather than merely "ported" or temporarily "deployed," it will be necessary to establish appropriate facilities, including ammunition depots, and additional measures, such as consultations on safe handling and strengthening security systems, will also be necessary. There would also have to be discussions on how to share costs with the U.S.

If Japan goes as far as "nuclear sharing," it will itself be involved in the actual operation of nuclear weapons in some way. The Constitution of Japan does not explicitly prohibit the possession of nuclear weapons, but at the same time, the possession of so-called “offensive weapons designed to be used only for the mass destruction of another country" is considered a violation of the Constitution as exceeding “the minimum necessary level” for self-defense¹⁹. It would be necessary to sort out in terms of constitutional interpretation whether the existence of nuclear weapons that would be involved in their operation through "nuclear sharing" would not fall under this category. It would also be necessary to determine whether the Atomic Energy Basic Act (Article 2), which stipulates the peaceful use of nuclear energy, would be violated. It may be possible that a revision of the law is required. While it is generally understood that "nuclear sharing" does not violate the nuclear Non-Proliferation Treaty (NPT), it will be necessary to carefully explain this to the international community once again.

A detailed study of how nuclear weapons would actually be operated would also be essential. Under what circumstances would nuclear weapons be provided by the U.S., and what kind of decision-making or command and control system would be used by the Japanese side? The operation of nuclear weapons requires direct decision-making by the supreme leader of any nation, and it is necessary to establish a command and control system for nuclear weapons (NC3) that is distinct from that for conventional forces. In Japan, for example, it would be necessary to consider whether a device like the "Nuclear football" in the United States (or the "Cheget" in Russia) should always be placed around the prime minister, and how the NC3 system should be differentiated from that of conventional forces. In addition, since the national leaders involved in the operation of nuclear weapons and their surroundings are vulnerable to so-called "decapitation" attacks by adversaries, it will be necessary to devise how to prevent such attacks and, if they should occur, how to ensure a smooth succession of commanding chain to a lower level of successors. Furthermore, it will be necessary to determine how to select targets for nuclear weapon operations, how much to rely on the cyber and space domains, how much to allow the use of AI, how to protect nuclear forces, and whether existing defense plans for conventional forces need to be revised for this purpose. Furthermore, it will be necessary to implement these series of initiatives in step with the U.S.

The discussion of additional issues does not end here. To put it in terms of the indirect issues involved, for example, even the question of whether to change the legal status of the Tsugaru Strait, etc.²⁰, which have been positioned as "the designated areas" because of the "three non-nuclear principles," might be a subject of discussion. A more comprehensive discussion is beyond the scope of this article, but in any case, what is emphasized here is that even if we speak of "nuclear sharing and nuclear introduction" in one word, it is essential to consider a large number of additional related issues in advance if we really want to realize such a plan.

The issue of "nuclear sharing and introduction" raised by Prime Minister Ishiba in the LDP presidential election debate and in his writing to the Hudson Institute is a serious security policy issue that could determine the future survival of Japan. For this reason, there are several points that must be kept in mind when seriously discussing this issue.

This article attempts to summarize the points that need to be kept in mind when discussing the issue. In order to discuss the issue of "nuclear sharing and nuclear introduction"; (1) it needs to be positioned as a medium and long-term issue, (2) it is necessary to sort out whether it should be done bilaterally between Japan and the U.S. or multilaterally, (3) it is necessary to clarify what kind of "nuclear sharing and nuclear introduction" should be specifically aimed at, (4) it is necessary to discuss what the optimal form of "nuclear sharing and nuclear introduction” in the Indo-Pacific theater should be, (5) it is necessary to clarify why it is required in the first place, and (6) it is necessary to consider additional related issues in advance.

For a long time, Japan has had little opportunity to discuss how to maintain the credibility of extended nuclear deterrence from the standpoint of being the "only atomic-bombed nation in the world.” However, changes in the regional situation, including China's rapid expansion of its nuclear arsenal, have strongly prompted Japan to reconsider its past stance. The issue of strengthening the credibility of extended nuclear deterrence, including "nuclear sharing and introduction," is first and foremost an issue that must be raised by the allies themselves, who are seeking enhanced deterrence and reassurance from the U.S. Without a serious and concrete proposal from the allies, the U.S. is unlikely to respond to the consultations and requests. In this regard, Japan must first engage in discussions in Japan based on knowledge at a level comparable to that of the U.S. I hope that the discussion points outlined in this article will be of help in this regard.