• Despite Japan's decision not to sign the TPNW, the promotion of nuclear disarmament remains one of the top priorities of Japan's foreign and security policies.
• As the adoption of the TPNW has further widened the rift between nuclear-armed/umbrella states and other non-nuclear-weapon states, Japan should make efforts to bridge the two sides.
• It is imperative to continue striving to improve the security environment and to clarify the aims of deterrence even under the current security circumstances where strengthening deterrence is required.

Japan reaffirmed its decision not to sign the Treaty on the Prohibition of Nuclear Weapons (TPNW) immediately after its adoption on July 7, 2017. The reasons for this decision, which Japan has repeatedly explained, are, inter alia, that the TPNW has not gained the understanding or the involvement of any of the nuclear-armed states; that the treaty would lead neither to the solution of real security issues such as the North Korean nuclear problem nor to an actual reduction in the numbers and/or roles of nuclear weapons; and that adopting the TPNW would just widen the divisions over the notion and policy of nuclear disarmament between nuclear-armed and umbrella states on the one hand and other non-nuclear-weapon states on the other.

Another crucial reason for this decision, which the Japanese government has emphasized less, is that Japan relies on the US' extended nuclear deterrence (nuclear umbrella) for its national security. Conclusion of the TPNW would not diminish the potential and overt nuclear threats posed by Japan's three neighbors possessing nuclear weapons, namely North Korea, China and Russia. In the face of such circumstances and with those nuclear threats actually increasing, joining the TPNW — which legally prohibits reliance on nuclear deterrence but offers no adequate alternative to extended nuclear deterrence — can hardly be said to be a realistic security policy for Japan.

Needless to say, Tokyo's attitude vis-à-vis the TPNW does not mean that it has shifted its position to disvalue nuclear disarmament. Japan shares with proponents of the TPNW their views on the importance of achieving a total elimination of nuclear weapons as well as their frustration over the paralysis of nuclear disarmament. As the only country to have ever suffered from the devastation of the dropping of atomic bombs, Japan is more acquainted than any other country with the humanitarian dimensions of nuclear weapons; this is precisely why it has consistently aspired to achieve a world without nuclear weapons. At the same time, nuclear disarmament also represents for Japan an imperative means of bolstering its national security as relationships with the abovementioned nuclear-armed states have been rather unstable. Revitalizing nuclear disarmament remains one of the most significant issues in Japan's foreign and security policy.

However, the real problem here is how best to make nuclear disarmament a reality. Unfortunately, there is no panacea. A long list of nuclear disarmament measures that the international community should implement has been repeatedly presented for decades, including, inter alia, transparency and confidence-building measures by nuclear-armed states; further reduction by the US and Russia of their nuclear weapons; restraint by other nuclear-armed states in increasing their nuclear arsenals; early entry into force of the Comprehensive Nuclear-Test-Ban Treaty (CTBT); immediate commencement of negotiations on a Fissile Material Cut-off Treaty (FMCT); development of nuclear disarmament verification technologies; and resolution of security issues hampering nuclear disarmament. Nevertheless, it is not easy to foster momentum toward nuclear disarmament within the current security environment. Moreover, achieving a world without nuclear weapons will take a considerable amount of time. If removing the risks posed by nuclear weapons in just one big leap is not realistic, there is no other approach but to alleviate them in a gradual manner.

Therefore, it becomes vital to continue encouraging both nuclear-armed and non-nuclear-weapon states to undertake even small but nonetheless concrete and practical measures under the progressive approach that Tokyo has been advocating along with other nuclear umbrella states.

In order not only to stave off further widening the rift between nuclear-armed/umbrella states and other non-nuclear-weapon states but also to bridge the two sides, Tokyo can take the initiative, as a symbolic but still important initial step, to reaffirm the two sides' commitments to eliminating nuclear weapons and start discussions aimed at converging their respective approaches toward that common goal. The Non-Proliferation and Disarmament Initiative (NPDI), which was initiated by Australia and Japan together with ten other non-nuclear-weapon states, both proponents and opponents of the TPNW, could be a useful platform for such efforts.

In the meantime, there may be future circumstances where maintaining and strengthening deterrence becomes inevitable, as it is currently. At the same time, however, one needs to keep in mind that strengthening deterrence poses the potential risk of triggering an arms race. Therefore, with the current security situation in mind, Japan, along with the United States as its ally, needs to continue clarifying its intention to bolster deterrence, aiming to prevent provocation and aggression as well as maintain international/regional order; reassuring other countries that it will not threaten their legitimate national interests; taking further efforts to improve the current security environment; and promoting nuclear disarmament more proactively.

Hirofumi Tosaki is a senior research fellow of the Center for the Promotion of Disarmament and Non-Proliferation, The Japan Institute of International Affairs.

The views expressed in this piece are the author's own and should not be attributed to The Association of Japanese Institutes of Strategic Studies.