For thousands of years, besieging armies sought to cut the water supplies to walled cities to break down their resistance. No matter how brave, a warrior could not fight without water, and the women and children he defended could not live long without it. The 21st-century-warfare version of depriving a city of water will be to deny entire states the ability to process, protect, and communicate information.

The astonishing thing about last spring's alleged Russian cyberattack wasn't the crippling effect it had on Estonian's government and the lives of its citizens but the lack of serious reaction elsewhere. The European Union raised but one scolding finger, NATO sent a few experts to the Baltic nation, and the US protested mildly and briefly — then President Bush welcomed Putin to the Bush family compound in Kennebunkport, Maine. In fact, as the world witnessed the trial run of a new mode of warfare, pundits at The New York Times and other publications dismissed the digital assault on the tiny nation as much ado about nothing. Those what-me-worry voices miss three critical points:

First, Estonia's advanced state as an e-society makes it appear uniquely vulnerable, but a full-scale cyber attack on the US could be far more devastating. Beyond the at-risk civilian sector, our armed forces rely on digitized information and communications to fuel their high tech hardware. If petroleum was the indispensable asset that decided campaigns in World War II, today the key is a military's ability to collect, compute, communicate, and shoot. If the computers don't work, the bombs don't strike their targets.

Insiders acknowledge that the Department of Defense is worried about the vulnerability of its networks and weapons systems, and defensive security is being tightened. At the same time, officials are developing offensive methods, though these black programs are classified. Still, the Pentagon doesn't seem to fully grasp the dangerous potential of this new domain of warfare. If you follow defense- budget dollars, funding still goes overwhelmingly to cold war era legacy systems meant to defeat Soviet tank armies, not Russian e-brigades.

Second, in an all-out conflict, digital attacks would not occur in a vacuum. A basic military law is that all weapons are most effective when used in incisive combinations with others. In a major war, Beijing would also attempt to physically destroy the satellites our forces rely on to communicate, find the enemy, and guide precision weapons. Whether attacking military targets or civilian systems, the Chinese would combine virtual destruction with actual destruction.

A decade ago, Chinese military theorists like the infamous colonels Qiao Liang and Wang Xiangsui were already hinting at the importance of simultaneously striking multiple infrastructure layers in a confrontation with the US. In theory, the breakdown of one system would compound the effects on another, and the crippling of energy, government services, communications, the media, and health care and finance systems would interact in a downward spiral.

Finally, informational dependencies and e-attack methodologies are advancing exponentially; the more complex our society becomes, the greater its inherent vulnerabilities (a law that software writers certainly understand). A digital assault today would outrage and inconvenience Americans, but we'd pull through. Tomorrow could be different. Military technologies and techniques can develop with distressing speed: In 1918, those rickety World War I airplanes were little more than romantic irritants; by 1943, a mere quarter-century later, long-range bombers were flattening entire cities. And the pace of technological change today is considerably greater than it was in the 1920s and 1930s.

The military maxim that applies is that, while you may hope for the best, you had best prepare for the worst (a principle violated, fatally, in Iraq). If the US vigorously pursues offensive and defensive e-war capabilities but the skeptics turn out to be right, we will have wasted only time and money. But if the US doesn't prepare and those who dismiss the digital-warfare threat are wrong, we might face a devastating surprise attack. To borrow a line from Frank Zappa, Pearl Harbor might look like "strictly a pup-tent affair."

A well-prepared, resourceful opponent could create an atmosphere of collapse, as America's most-advanced military systems failed, citizens panicked, and the economy froze. The enemy's goal would be to pressure Washington into an early settlement that amounted to a de facto surrender.

But Americans are far tougher than commonly perceived — after all, history's greatest losers are those who bet against the US. Still, the current asymmetry between the no-holds-barred approach to cyberwar embraced by potential enemies and our own insistence on confining all forms of warfare within antiquated laws would put us at a painful disadvantage in a conflict's opening phase. The rest of the war would be longer, more destructive and far more vicious than it would have been had the US been prepared.

*Ralph Peters, a retired Army intelligence officer, is the author of 22 books; his most recent is *Wars of Blood and Faith: The Conflicts That Will Shape the 21st Century.

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