That barrier is hardly unbreachable, but it would demand quite a feat of political persuasion on Tokyo's part. As the learned strategist Mike Tyson points out, "everyone has a strategy 'til they get punched in the mouth." Memo to nuclear-weapons advocates: duck!
Nor are the strategic, operational, and technical challenges less daunting. A nuclear triad — land- and sea-based missiles combined with weapons delivered by manned bombers — holds little promise in light of Japan's lack of geographic depth and the vulnerability of surface ships and aircraft to enemy action. That means fielding an undersea deterrent would be Tokyo's best nuclear option. But doing so would be far from easy. The Japan Maritime Self-Defense Force operates an impressive fleet of diesel submarines but has no experience with naval nuclear propulsion. And that leaves aside the difficulty of developing sea-launched ballistic missiles and their nuclear payloads.
Such engineering challenges are far from insoluble for Japan's scientific-technical complex but cannot be conquered overnight. A force of nuclear-powered ballistic-missile subs, or SSBNs, thus looks like a remote prospect for Japan. As an interim solution, the JMSDF might construct cruise missiles resembling the U.S. Navy's old TLAM-Ns, or nuclear-tipped Tomahawks. JMSDF boats could fire such missiles through torpedo tubes, the easiest method. Or, shipyards could backfit Japanese subs with vertical launchers — much as the U.S. Navy installed Tomahawk launchers in its fast attack boats starting in the late Cold War.
The problem of constructing nuclear weapons small enough to fit on a missile would remain — but nuclear-armed diesel boats would represent a viable course of action should Japan decide to join the nuclear-weapons club. Years down the road, then — not overnight — a modest Japanese nuclear deterrent might put out to sea. Will Tokyo proceed down that road? I doubt it. But the prospect no longer appears unthinkable.
