Defend the First Island Chain

A strategic solution to the troubled waters of the Western Pacific is perimeter defense—but what kind? History offers options.

Want to give China an ulcer, a nagging sore that compels Beijing to think twice about aggression? Then look at the map. Geography affords the U.S.-Japan alliance abundant opportunities to make trouble for the People’s Liberation Army (PLA), denying China’s military access to the vast maneuver space of the Western Pacific while hampering its movements up and down the Asian seaboard. Fortifying the offshore island chain while deploying naval assets in adjoining waters could yield major strategic gains on the cheap. Doing so is common sense. The only question is how.

One imagines the greats of strategy would agree. Sage Carl von Clausewitz instructs statesmen and commanders to size up the “strength and situation” of each competitor before embroiling themselves in power politics. Net assessment is basic for him. Savvy competitors turn their physical surroundings to advantage, harnessing geographic features to block enemy movements altogether or channel them into predictable pathways where attackers can be met and overpowered. At sea, imaginative use of islands and passages can balk an adversary’s strategy if that strategy depends on free movement through nearby waters. Terrain, then, can offset an opponent’s advantages in numbers of ships, aircraft, or manpower. Used deftly, it can produce a margin of superiority at places where it matters most.

And that’s the crux of things, isn’t it? For Clausewitz there’s no higher or simpler law than to make oneself strong at the decisive place and time. Doing so—displaying imposing capabilities while telegraphing the resolve to use them—improves the prospects for deterring opponents, and thus for preserving peace. It’s high time for the U.S.-Japan alliance to heed the wisdom of this long-dead Prussian in the strategic competition with China. Islands bristling with antiship and antiair weaponry can cast a long shadow over sea passages, making themselves strongpoints in an offshore barricade while creating overlapping fields of fire. Mines, submarines, and fleet-footed surface craft dispersed around the islands can make things even tougher on PLA forces.

Best of all, these are low-cost measures that compel China to mount countermeasures at high cost to itself, and with doubtful efficacy. The value a combatant assigns its goals usually governs how many resources it puts into a martial endeavor, and for how long. The more valuable a political aim, the more lives, treasure, and weaponry it expends on behalf of that aim. But as Clausewitz notes, warring states have been known to limit an effort not by ends but by means. He terms this “war by contingent.” That is, a government caps the amount of resources it’s willing to spend on an enterprise ahead of time. It then looks for ways to wring maximum bang out of this predetermined number of bucks. Ingenuity and operational dexterity are at a premium as the contingent searches out ways to create outsized problems for and impose outsized costs on the adversary.

Asia’s “first island chain,” to borrow the ubiquitous Chinese phrase, encloses the East Asian coastline. It arcs southward from the Japanese home islands through the Ryukyu Islands, Taiwan, and the Philippine archipelago. Each annual Pentagon report on Chinese military power, moreover, includes a map that traces the island chain from the Philippines westward to central Vietnam. Interpreted thus, and sealed off by the occupants of the islands, the chain would present a formidable barrier to exit from or entry into the China Seas. This is an ideal opportunity for mischief-making at the PLA Navy’s expense. Contingents scattered on and around the islands and straits comprising the first island chain could give Beijing a bad day should things turn grim over the Senkaku Islands, Taiwan, or some other geopolitical controversy.

Let’s consider how defenders can put geographic features to optimal use. Waging war by contingent along the island chain poses a problem of perimeter defense. Protecting a long, distended perimeter is hard. Think back to freshman calculus. A line is made up of infinitely many points. Now transpose that insight to a defense line. Trying to defend a perimeter means trying to be strong at every point along the curve. Few armed forces—least of all those waging war by contingent—sport the manpower or assets to pull off such a feat. If they make the attempt, they risk thinning themselves into irrelevance. An antagonist will simply mass superior force somewhere along the line and punch through.

Vice Admiral Yoji Koda, a former commander of Japan’s Self-Defense Fleet, deprecates the value of forward defense perimeters in the crowded confines of Asia. For China to view the first island chain, including Japan, as an outer defense line has “no significance.” This, he writes, would be like Tokyo’s fixing its defense perimeter at the Great Wall. That’s strategic gibberish. No nation can defend itself forward into another’s territory. But from an operational standpoint, the narrow seas piercing the island barrier are of enormous consequence for the power boasting the military capacity to control them.

Imperial Japan sketched an outer defensive perimeter, enclosing most of the Western Pacific, during World War II. Admiral Koda notes ruefully that the Japanese defense line barely hindered the U.S. Navy from breaking into Asian waters. But this stands in stark contrast to the first island chain, a short, relatively defensible line along closely grouped islands. Even Koda, an avowed island-chain skeptic, concedes that the U.S.-Japan alliance can turn maritime terrain to advantage in its competition with China.

The question now is, how should the allies tap the strategic potential of the islands? What sea areas do they want to manage, where should they station contingents for maximum effect, and what forces should constitute these contingents? Surveying history reveals three basic outlooks on how to use walls and other defense perimeters:

• A weaker defender worried about safeguarding territory behind a frontier may construct a defense line to slow down enemy forces and compress them into well-defined lanes where lesser forces can stymie or defeat them. The assumption is that a stronger enemy will get through.

• Defenders can attempt to create a rigid, impenetrable shield against enemy passage. Stopping an advance in its tracks is the goal.

• Or they can use a defense perimeter as a platform for forays into enemy-held territory beyond the perimeter. The barrier furnishes a backstop for offensive actions. It’s commonplace to view a barrier as a passive thing behind which defenders shelter. It may be anything but. The value of a defensive barrier derives not just from stout construction but from the balance of strength between the contending sides.

Let’s take these general ideas in turn. The first model might be dubbed the Great Wall model. In The Great Wall of China: From History to Myth , University of Pennsylvania professor Arthur Waldron debunks traditional claims that China’s Great Wall dates from remote antiquity. Rather, he writes, it was the Ming Dynasty (1368–1644) that consolidated and improved preexisting works into a formidable barrier against armed raids and incursions from the north.

Despite the Great Wall’s imposing appearance, however, it is an artifact not of Ming strength but of Ming weakness. Its purpose was less to stop all breaches than to confine and delay attackers—giving mobile striking forces stationed behind the wall time to amass superior might at embattled points. Strong, virile powers seldom entrust their security wholly to passive defenses such as walls. Decaying or temporarily outmatched powers may.

The impenetrable line is the second type of perimeter defense. History has witnessed any number of attempts to stage such defenses. Of them, France’s Morice Line, erected to seal the border between Algeria and Tunisia during the French-Algerian War (1954–1962), ranks among the most successful. It combined electrified fortifications with electronic detection devices and minefields, putting in place a truly forbidding barrier. Indeed, Algerian nationalist forces threw themselves against the Morice Line to little avail. It approached perfection as perimeter defenses go, relative to the opponent.

Though built to inhibit enemy movements on land, the Morice Line—an elaborate array of defensive works built to hold a line in the sand—shows that defense perimeters may be feasible at sea given sufficient resources, high technology, and political resolve. If armies can mount a perimeter defense in the desert, maritime forces may be able to do so in Asia’s near seas.

Unlike the North African hinterland, after all, the near seas represent a geographically cluttered operational setting featuring natural guard towers and narrow defiles—islands and straits, in other words. Such a setting could let the islands’ defenders cordon off the China Seas. They could block PLA Navy egress from these waters. Or, they could keep ships plying the Pacific or Indian oceans before the outbreak of war from returning to home waters. Either way, a nautical Morice Line could pay off handsomely, especially considering the modest investment it would demand.

We might call the third type the Hadrian’s Wall model. Roman forces overran most of Britain two millennia ago but elected to fence off present-day Scotland rather than try to complete their conquest of the island. Stretching from east to west across the narrow neck of northern Britain, Hadrian’s Wall supplied a backstop against serious enemy efforts at a breach. Yet it was largely a staging place for offensive operations.

This was a wall-building strategy of the strong, as strategist Edward Luttwak recounts in The Grand Strategy of the Roman Empire . Forward defense kept Celtic foemen off-balance while creating a buffer to inhibit encroachment toward the defense line. Wall-building is intrinsically defensive in nature, then, but the Romans gave it an offensive twist. Forward defense denied adversaries the luxury of acting with impunity—even on their own home ground.

A Hadrian’s Wall approach to maritime defense—a highly active, offensive-minded defense—would attempt to deny the PLA access to its own home waters. It would turn the logic of access denial—the approach China has taken against the U.S. Navy and Air Force on the macro level—against China on the micro level. Deterrence might prevail. Failing that, the allies will have positioned themselves for success should Beijing opt for a trial of arms.

Granted, these analogies all come from land warfare. And indeed, as Alfred Thayer Mahan points out, the open ocean is like a featureless plain. It’s hard to string a picket line across such emptiness. As Admiral Koda observes, Imperial Japan’s outer defense perimeter proved unenforceable with the resources Japan’s navy had to deploy. Near shore, however, the resemblance between sea and terrestrial combat is striking. That’s doubly true in East Asia, with its complex strategic geography. In Naval Strategy , his last major work, Mahan spilled a vat of ink showing that marine warfare resembles land warfare in coastal zones. Perimeter defense can work under special circumstances—circumstances such as those prevailing in maritime East Asia.

Perimeter defense, then, comes in multiple varieties. A Great Wall defense would be oriented more toward the Western Pacific, with a view toward safeguarding those waters for allied fleets and air forces. Preserving that maneuver space would let forces surge to points of impact, moving around behind the island chain. A Morice Line strategy would concentrate mainly on holding the line along the island chain. And a Hadrian’s Wall strategy would look inward toward continental Asia, both to stage a forward defense of the islands and straits and to interdict north-south movement through the China Seas.

Which model should the allies embrace? Which best meets Clausewitz’s standards for war by contingent, namely economical cost to the allies, prohibitive cost to the opponent, bearable risk of escalation, and disproportionate strategic gains? Or does some hybrid approach hold the greatest promise? If war by contingent—again, war waged by the means allotted rather than the ends being sought—is the answer, then the questions revolve less around politics and grand strategy than around doctrine and force structure. Those questions include:

• What Are the Limits of the Possible? How many assets, seagoing and shore-based, are in the allied inventory for shaping events in the straits’ and the island chain’s maritime environs? In other words, how robust and numerous can contingents fielded along the Ryukyus be? And how many heavy forces—surface combatants, nuclear-powered attack boats, and so forth—can the allies allocate to back up these defenders?

• How Much Pushback Is Likely? What is the local balance of forces between China and the U.S.-Japan alliance, factoring in commitments in other theaters that could siphon off American or Chinese resources? If the allies deem themselves to hold a strong position, a more aggressive perimeter strategy may be preferable. If a weaker position, a more passive, reactive strategy may be their best if not only recourse.

• Can Advantages Be Extended and Disadvantages Overcome? What are the trend lines in the maritime balance? Can the allies flatten out or reverse unfavorable trends while widening favorable ones?

• How Fast Can the Allies Improve? If so, how quickly can any shortfalls in force structure and island-chain defense doctrine be remedied, given political and budgetary realities in allied capitals? Can the allies move from a more passive to a more active defense? Or will unfavorable trends in the military balance, whether through technological change or sheer weight of numbers on the PLA side, compel them to retrench?

While war by contingent inverts the usual supremacy of ends over ways and means, however, there is no escaping diplomatic and grand-strategic factors. Here are some big-think matters Washington and Tokyo might ponder as they weigh which stance to take:

• Will Allied Unity Hold? The two countries should ask themselves to what degree they will remain united behind their political and strategic aims. It is entirely possible, for instance, that Japan will attach greater importance to holding the island chain than will faraway America. Indeed, Clausewitz notes laconically that no nation attaches the same importance to another’s cause that it attaches to its own. The allies must be frank with one another in strategic councils rather than paper over their differences. Let’s be a bit undiplomatic with each other beforehand rather than suffer unpleasant surprises after the shooting starts.

• How Provocative Are They Willing to Be? The allies must afford the potential red team close scrutiny, and respect its capacity to block their plans. Beijing is not a potted plant. If Washington and Tokyo can threaten to impose high costs on the PLA, Beijing can reciprocate with threats and counterstrategies of its own. The allies must attempt to gauge China’s preparedness to escalate the conflict over attacks on its naval shipping, and they must estimate their own tolerance for the risk and dangers of escalation. Thinking ahead about likely action/reaction dynamics is a must.

• How Will Third Parties Respond? Clausewitz exhorts statesmen and commanders to mull the possible impact of their actions on third parties able to influence the outcome. What responses may such actions summon forth? If Washington and Tokyo elected to extend their island-chain defense southward to, say, the Luzon Strait, considering what reactions such a move would provoke from Taiwan and the Philippines would be essential. China and the allies are far from the only players with a stake in this game. Neglecting the others would represent a grave mistake.

What about hardware and tactics? How should allied contingents be configured? The implements for executing a perimeter defense would be largely the same, no matter which model the allies alight upon. Quantity—manpower, ships and aircraft, weaponry and logistical support—would be the crucial difference between Great Wall, Morice Line, and Hadrian’s Wall forces. The more assets earmarked for island-chain defense, the more vigorous and forward-leaning the posture the allies can assume. They can mix-and-match forces depending on the defensibility of nearby islands and the width, length, and undersea terrain of the sea passages themselves.

Sea mines would be an obvious choice for any of the three strategic options. Cheap and lethal, they can be arranged into minefields to interdict naval movements. Mine warfare capitalizes on the PLA Navy’s relative, and puzzling, neglect of mine-hunting and mine-sweeping. With their silence, slow speeds, and shallow drafts, diesel submarines would make excellent unseen pickets. They could either prowl behind a nautical Great Wall, range the China Seas before a Hadrian’s Wall, or both if numbers permit. This too exploits a PLA Navy blind spot: antisubmarine warfare. And small, missile-armed patrol craft—counterparts to China’s Type 022 Houbei catamarans, or Taiwan’s stealthy Hsun Hais —could roam the coastal waters around the islands, using land features for concealment and protection while dishing out punishment against PLA Navy surface ships.

Last but not least, the islands themselves must be defended—both because seizing one of them could offer China its best chance of breaking through the perimeter, and because they provide emplacements for mobile antiship and antiair missiles. The Japan Self-Defense Forces (SDF) already field a truck-launched antiship cruise missile, the Type 88, and are reportedly readying an extended-range variant. Small bodies of missile-armed SDF troops dug in along the island chain would complete this murderers’ row. Such defenses would give PLA commanders and their political masters pause before attempting a breakout, and exact a heavy toll if they proceed.

Marrying up warriors and their weapons with geography affords the U.S.-Japan alliance its greatest prospects for giving China a nasty ulcer in wartime—and thus for preserving the peace.

Dr. Holmes is professor of strategy at the Naval War College and coauthor of Red Star over the Pacific , named to the Chief of Naval Operations’ Professional Reading List as “Essential Reading.”