Japan could win a war for the Senkaku islands, but it wouldn't be easy. And certainly not without U.S. help.
In recent weeks, Japan and China have squared off over who owns a minor group of islands in the East China Sea. The unthinkable — a perilous maritime war for seemingly trivial stakes — no longer appears unthinkable. So how do you defend a group of uninhabited rocks and islets like the Senkaku/Diaoyu islands?
Mainly by positioning yourself to win the air and sea battle around the disputed archipelago. The obvious way to ward off attack — stationing garrisons and artillery on the tiny, resource-poor islands — should be a secondary measure. And it would likely prove a losing one, absent superiority in nearby seas and skies. Forces left ashore without external support would find themselves stranded and outgunned, not to mention hungry and thirsty.
To be sure, heavily armed ground detachments can convert islands with rugged terrain into virtual "porcupines," prickly to the touch. For instance, Japan Ground Self-Defense Force (GSDF) troops equipped with truck-launched anti-ship cruise missiles could give any naval assault force fits. They could dig in, hardening their positions against air and missile bombardment. Despite their small numbers, GSDF defenders would be exceedingly tough to dislodge.
But only for a time. Whoever controls the sea and sky will ultimately determine the islands’ fate. If U.S.-Japanese naval, air, and ground forces can hold open access to the islands while fending off Chinese assailants, the allies would stand to win a limited clash. They can resupply defenders perched there, letting them hold out more or less indefinitely. But if China’s People’s Liberation Army (PLA) wrests control of the air and sea commons from the allies, on the other hand, it will be at liberty to cordon off the islands and starve out the defenders. And then Beijing will stand to win.
Were a battle over the Senkakus/Diaoyus to take place today, I would give China the edge, even though Japan holds the contested real estate and the United States has committed itself to the islands’ defense. Geography and force are the main reasons why.
First consider the islands’ geographic merits and drawbacks. The great fin de siècle seapower theorist Alfred Thayer Mahan classifies geostrategic assets by their position, strength, and resources. The Senkakus/Diaoyus occupy an awkward position near the southern tip of the undefended Ryukyus chain, closer to Taiwan than to the Japanese main islands and roughly equidistant between Okinawa and the Chinese mainland. The archipelago’s natural defenses are so-so at best, owing to its small size and fragmentation into several islets.
The island chain’s geography opens up options for a determined attacker. Rather than mount a full-scale assault, PLA occupiers could grab one island, place weaponry on it, and pummel Japanese GSDF sites from there — seizing the rest over time through salami-slicing tactics. And since the islets offer virtually no natural resources to support garrisons, everything would have to be shipped in by sea or air. If China rules even a pocket of sea and airspace around the islands, it will probably get its way in a test of arms.
In Mahan’s terms, the Senkakus/Diaoyus are like Gibraltar — without the ideal strategic position or the forbidding natural defenses. And like Gibraltar, they would be entirely dependent on outside logistical support in wartime. Their geostrategic potential is minimal by all three of Mahan’s measures.
Which leads to the configuration of forces. Mahan’s British contemporary and sometime rival, British theorist Sir Julian Corbett, observes that limited maritime war is the prerogative of the belligerent that can isolate the theater through naval action while shielding its homeland from an "unlimited," asymmetric counterstroke — a strike that would disarm its military from afar, unseat the government, or otherwise compel it to sue for peace.
The antagonist whose armed forces can make the sea an "insuperable physical obstacle" to enemy action enjoys the luxury of concentrating overpowering military might at decisive points in the theater — improving its expeditionary forces’ prospects of attaining operational, strategic, and political goals. The U.S.-Japan alliance is unlikely to escalate to strikes against the Chinese mainland for the sake of the Senkakus/Diaoyus. Japan has little capacity to mount such a threat, whereas the logic of nuclear deterrence eliminates any real chance of the United States’ doing so. And thus, if the PLA can seal off the archipelago, it will meet Corbett’s standard for limited war. The allies will never fully meet that standard.
If Tokyo wants to hold the islands over the long term, then, it needs to do some basic things. First and foremost, Japanese commanders and officials must figure out how to pry open and keep open access to the islands should the PLA actively dispute their access — as it will, should China and Japan come to blows. Local command of the commons may demand staging naval and air forces in and around the Ryukyus, closer to the likely scene of combat.
Second, Japanese commanders must consider how to bar Chinese access to the embattled area. For example, deploying mobile anti-ship missiles on Yonaguni Island, at the extreme southwestern tip of the Ryukyus, would allow the GSDF to hold Chinese surface ships at risk around the Senkakus/Diaoyus. Stationing weaponry on the islets themselves would generate overlapping fields of fire. Mining nearby waters is worth considering, as is building large numbers of small, stealthy combatant ships armed with anti-ship missiles. Swarms of unobtrusive but deadly small craft could ruin Chinese commanders’ whole day. Indeed, Beijing has premised its "anti-access" strategy vis-a-vis the U.S. Navy in part on such craft. Tokyo can take a page from Beijing’s book, fashioning a small-scale, anti-access zone of its own.
Finally, Japanese officials must not overlook the politics of island defense. Blunting a PLA offensive may not come cheap, either in the Senkakus/Diaoyus or elsewhere. It is high time for Japan to reconsider its unofficial cap on defense spending, which has stood at 1 percent of gross domestic product for decades. This is not a serious enough commitment for a nation facing Japan’s geostrategic predicament.
And however sincere Washington’s assurances about helping defend the archipelago, Tokyo should not bank on its doing so with any real enthusiasm. U.S. leaders will not attach the same value to the Senkakus that Japan does. That disparity is apt to beget differences within the alliance over strategy and operations. To keep open their options, Japanese leaders should think ahead toward fielding weaponry and developing strategy for going it alone.
Defending these uninhabited islets, then, represents a microcosm of the larger dilemmas confronting Japan in maritime strategy. It poses a test of a high order for the Japanese military services — and for the nation as a whole.