In March of 1999, the U.S. Marines invaded California. Descending on an old Navy hospital in Oakland, they attempted to wrest it from guerilla fighters encamped there. Despite being armed to the teeth with the latest intelligence-gathering and assault weaponry, they suffered devastating losses, some units reporting casualty rates as high as 70 percent after just a few hours of fighting.

The Oakland raid was an exercise, of course, and no one actually died. But it drove home an important lesson, and one that military experts have harped on for years: despite all its advanced technology and extraordinary fire power, the U.S. military is ill-prepared to wage an urban war. Nor is it alone. Russian troops succeeded in routing Chechen fighters from the capital city of Grozny only after flattening whole neighborhoods and killing thousands of civilians. The last decade has seen similarly destructive campaigns waged in Sarajevo and Mogadishu and many other cities around the world.

"Virtually every recent U.S. military operation has had an urban component," noted Russell Glenn, a senior research analyst and urban warfare expert at Rand Corp., Santa Monica, Calif. "It's not something that we can afford to be casual about."

Not that there's any good place to hold a war, but, in terms of lives lost and property destroyed, cities are the most costly settings in which to do battle. Writing some 2500 years ago, the Chinese military strategist Sun Tzu warned, "The worst policy is to attack cities. Attack cities only when there is no alternative."

As it happens, though, the likelihood of urban warfare will only grow in the coming years. Half of the planet's people now live in and around cities, and by the end of the next decade, about 70 percent are expected to do so. Accordingly, the U.S. military, and to a lesser extent its counterparts in Israel, Australia, and several NATO countries, have been taking a good hard look at how to win the next urban war. That entails developing new technologies to aid the urban warrior, revamping training programs, and rethinking the guiding doctrine underlying military operations.

High-density battles

What makes urban battles so thorny are their sheer complexity and unpredictability. "Think of it in terms of density," Glenn suggested. "Per unit volume, the city has more friendly forces, more enemy forces, more noncombatants, more firing positions, more enclosures." What's more, the technological edge that well-armed troops normally enjoy grows noticeably duller in the city. Long-range artillery is too destructive and imprecise, tanks cannot negotiate narrow streets, radio and navigation signals falter inside buildings and underground.

Nowhere were the limits of technology more apparent than in the United States' disastrous mission in Mogadishu in 1993. In that battle, some of the best-equipped, best-trained soldiers in the world went up against a rag-tag militia—and lost. Using simple rocket-propelled grenades, Somali fighters downed two state-of-the-art Blackhawk helicopters and damaged three others. In a single day, 18 U.S. soldiers and some 500 civilians died.

One of the many things that tragedy taught was the importance of the psychological dimension in urban war. U.S. soldiers had expected to find a receptive civilian population, and so were shocked when unarmed but hostile mobs began harassing them. "We have to put ourselves in the other guys' shoes, because they're going to use things against us that we haven't even thought about," noted George Singleton, a national security expert at the U.S. Oak Ridge National Laboratory in Tennessee, who did a case study of the Mogadishu firefight.