Island-Chain Defense

A marine affairs expert claims the concept of island chains has no strategic significance. He may be half-right.

It never ceases to astound me how malleable our views of seemingly fixed things like geographic features can be. Like many on the Naval War College faculty, I’ve long been a fan of retired Vice Admiral Yoji Koda, a former commander of the Japan Maritime Self-Defense Force (JMSDF) fleet and a learned commentator on marine affairs. His Naval War College Reviewarticle on the Russo-Japanese War of 1904-1905 is a staple of our Intermediate Level Course curriculum, and rightly so. Now a senior fellow at the Harvard University Asia Center, Adm. Koda recently presented me a copy of Harvard Asia Quarterly in which he appraises China’s naval rise from a Japanese standpoint. In the course of the article he makes a mystifying claim, categorically proclaiming that the concept of island chains has ‘no significance,’ from a ‘practical military strategy and planning point of view.’

Slap your grandma! quoth I upon reading this, reverting to the Southern vernacular on which I was reared. How could this familiar concept be utterly empty? Koda gives two reasons. He first observes that the lines describing the first and second island chains are ‘drawn on or in close vicinity of Japanese territories.’ Analysts of a geopolitical bent generally trace the first island chain along the Japanese archipelago, the Ryukyus, Taiwan and the Philippine archipelago. The second island chain meanders southward from northern Japan through Guam, terminating in the vicinity of New Guinea. To him it’s ‘meaningless’ to sketch defense lines on ‘non-allied foreign territory,’ presumably because one can’t count on having access to a potentially hostile nation’s soil. He likens it to a hypothetical decision on Cold War Japan’s part to inscribe an outer defense perimeter along China’s Great Wall and an inner perimeter along China’s East China Sea coastline. ‘Obviously, no one buys this idea.’

Koda is half-right. It’d be nonsensical, as he notes, to sketch a forward defense line through another nation’s territory. Land conquest would be required merely to reach one’s own forward defenses. This is rarely thinkable from a military let alone a political standpoint. But what about the other half of his analogy? Why couldn’t Japan or some other seafaring state—setting aside the politics of doing so—pronounce an adversary’s coast its own defense frontier? Indeed, there is ample precedent for seagoing states’ striking such a gung-ho attitude. Exhibit A: Great Britain’s Royal Navy in its heyday. Confident in their command of the sea, British seamen habitually proclaimed that they ruled the waves all the way up to an enemy’s shorelines, usually the Dutch, French, or Spanish coasts. So ingrained was this dogma that an exasperated Sir Julian Corbett declared that British commanders might as well open a naval campaign by singing ‘Rule Britannia’ as by uttering slogans like ‘the enemy’s coast is our frontier.’

And yet—Corbett’s protests notwithstanding—a sufficiently overbearing fleet could drive an enemy fleet from even its home waters. The Royal Navy pulled off this feat during the French Revolutionary and Napoleonic Wars, when the French Navy typically sheltered in port for fear of the beatings it generally took when it ventured within reach of British gunners. Similarly, JMSDF or US Navy commanders could declare the Chinese coast their frontier provided their service boasted the material superiority, tactical acumen, and seamanship to make good on such an aggressive doctrine. And conversely, there’s nothing illogical about Beijing’s inscribing a maritime defense line along the first island chain, including the Japanese home islands, should it choose to do so. Warships can lawfully approach within 12 nautical miles of any coastal state’s shores. And they can pass through the straits separating Japanese islands from one another, providing they restrict their activities. That’s mighty close quarters.

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An increasingly confident People’s Liberation Army Navy backed by shore-based missiles and aircraft might come to think—or talk itself into thinking—that it can extend its inner defense perimeter to within sight of the Japanese archipelago. All the more reason for Tokyo and Washington to shore up the balance of maritime power in Asia, lest Beijing believe the hype surrounding Chinese military might.

Second, Adm. Koda draws the analogy to Imperial Japan’s outer line of defense, the ‘Absolute Defense Perimeter,’ that more or less coincided with the second island chain. He rightly observes that the ‘existence of this line had given a certain “classroom” confidence to the Japanese military that it could defend its homeland at that difficult juncture of the war’—that is, from 1943 forward. US Navy carrier task forces ‘easily broke through’ the perimeter, rendering it ‘nothing but a pie in the sky.’ But aren’t the lessons simply that perimeter defense is hard and that unbroken lines on maps or nautical charts encourage overconfidence? If so, that’s a different claim entirely from Koda’s initial statement that such lines have no practical significance. Wartime Tokyo deluded itself into believing it could defend the outer line with dwindling forces. That’s an indictment of Imperial Japanese strategic wisdom, not of defense perimeters per se.

Strategic theorist Carl von Clausewitz offers useful insight into these matters, as on most strategic questions. Clausewitz deems the best strategy ‘always to be very strong; first in general, and then at the decisive point…there is no higher and simpler law of strategy than that of keeping one’s forces concentrated.’ It’s a relatively simple thing—although as Clausewitz also points out, ‘the simplest thing is difficult’ amid the stresses of combat—to be strong at a single point on the map or chart. But in calculus terms, being strong everywhere along a curve implies defending at a virtually infinite number of potential flashpoints along the perimeter. That strains the resources of the strongest military. Thus, as Koda concludes, history has generally been unkind to strategies of perimeter defense. They consume time, manpower, and inordinate resources.

To my mind, the sagest counsel is neither to lowball the rigors of perimeter defense, either for oneself or for prospective opponents, nor to rule it out entirely. Trying to defend everywhere is seldom a wise approach—but never say never.

James Holmes is an associate professor of strategy at the US Naval War College and co-author of Red Star over the Pacific, an Atlantic Monthly Best Book of 2010. The views voiced here are his alone.