Enhanced bilateral dialogue has been used to strengthen the alliance, but Japan’s neighborhood is more dangerous than ever, and the many domestic constraints on Japanese nuclear breakout—cultural, political, and institutional—could become less restrictive than before.
A U.S. decision to sustain extended deterrence will require significantly more resources and attention than heretofore assigned.
A more integrated, alliance-based approach to deterrence might therefore become attractive.
Alternatives to Japan’s long-practiced nuclear hedge may come to have appeal in Tokyo or Washington.
Coordinated regional action to limit North Korea’s nuclear development remains critical.
Japanese strategists have long been ambivalent about nuclear weapons. On the one hand, memories of horrific nuclear attacks on Hiroshima and Nagasaki have sustained anti-nuclear sentiment and helped justify national policies championing nonproliferation and forgoing an indigenous nuclear arsenal. This “nuclear allergy” has been diagnosed as a genetic condition, and associated institutional and diplomatic constraints on nuclear breakout have been invoked to predict that Japan will find it virtually impossible to reverse course on nuclear weapons.
Japan’s non-nuclear bona fides are well established. Until its revision in 2012, Article 2 of Japan’s Atomic Energy Basic Law (1955) stated clearly that research, development, and utilization of atomic energy was limited to peaceful purposes.  Japan joined the International Atomic Energy Agency (IAEA) in 1957 and has generously supported the agency’s work. After considerable debate and delay—and the receipt from the United States of much greater latitude for nuclear fuel handling and reprocessing—Japan ratified the Nuclear Non-Proliferation Treaty (NPT) in 1976 and supported the treaty’s indefinite extension in 1995. Japan also ratified the Comprehensive Nuclear Test Ban Treaty in 1997 and was the first to sign the IAEA’s Additional Protocol in 1998, allowing a stricter regimen for IAEA inspections of Japanese nuclear facilities.
Consequently, it was surprising to some in 2013 when Japan declined to join 74 other nations and sign a statement in advance of the next NPT review stating that nuclear weapons are inhumane and should not be used under any circumstance.  This illuminates the other, more realistic side of Japan’s approach to nuclear weapons. The Japanese government does indeed believe that some circumstances might warrant the acquisition and use of nuclear weapons, and the fact that Japan’s ability to act on this belief rests solely in U.S. hands is unnerving for certain politicians and bureaucrats in Tokyo.
Amid periodic reviews of the nuclear option in Japan, national policy has consistently depended on the “full range” of U.S. military might to deter nuclear attacks. This policy has been accompanied by frequent reminders to nuclear-armed rivals, as well as to Washington, that preemptive strikes and the use of nuclear weapons can be valid forms of self-defense. Japan has made it clear since the 1950s that it reserves the right (and will maintain the capacity) to develop a nuclear arsenal of its own. This strategy—“lying between nuclear pursuit and nuclear rollback”—is the essence of “the most salient example of nuclear hedging” among global powers. One Japanese analyst has framed Japan’s position on nuclear weapons as a balancing act between nuclear approval and nuclear denial. 
vOver the past four decades, Japan has maintained viable—and unconcealed—options for the relatively rapid acquisition of nuclear weapons and has justified its decision not to pursue nuclear breakout in many ways. But each time the regional security environment has shifted—such as after China’s first nuclear test in 1964, the end of the Cold War, North Korea’s nuclear…
 The U.S. intelligence community has assessed that “Iran’s nuclear decisionmaking is guided by a cost-benefit approach.” See Clapper, “Unclassified Statement for the Record on the Worldwide Threat Assessment of the U.S. Intelligence Community.”
 The 2012 amendment to the law adds “national security” as one of several reasons why nuclear safety should be guaranteed. Although the government and individual lawmakers claim this addition does not conflict with the “peaceful use” of nuclear energy, the revised law is arguably less clear on this point. See, for example, “‘National Security’ Amendment to Nuclear Law Raises Fears of Military Use,” Asahi Shimbun, June 21, 2012.
 “Japan Refuses to Back Statement against A-bombs,” Japan Times, April 26, 2013.
 This concept is introduced and developed in Ariel E. Levite, “Never Say Never Again: Nuclear Reversal Revisited,” International Security 27, no. 3 (2002/3): 59–88, 59, 71. Mike M. Mochizuki calls it “pragmatic pacifism” and argues that “it made sense [for Japan] to retain at least a latent capability to exercise the nuclear option.” See Mike M. Mochizuki, “Japan Tests the Nuclear Taboo,” Nonproliferation Review 14, no. 2 (2007): 311. Llewelyn Hughes rejects the term “nuclear hedging” but acknowledges that “the door to independent nuclearization [by Japan] remains ajar” and that “formal barriers to nuclearization are surmountable.” See Llewelyn Hughes, “Why Japan Will Not Go Nuclear (Yet): International and Domestic Constraints on the Nuclearization of Japan,” International Security 31, no. 4 (2007): 67–96, 69, 91.
 Yuri Kase, “The Costs and Benefits of Japan’s Nuclearization: An Insight into the 1968/70 Internal Report,” Nonproliferation Review 8, no. 2 (2001): 55.
[Free preview ends here. See purchase information above.]