The United States military is attempting to write a new chapter in the history of urban warfare.
For thousands of years, from the leveling of Troy by the Greeks around 1200 BC to the 17-hour firefight in Mogadishu that killed 18 US troops and hundreds of Somalis a decade ago, city fighting has been some of combat's bloodiest.
Now as US troops secure the outskirts of Baghdad and make targeted forays into the capital, the Pentagon will try to do in Iraq what has never been successfully accomplished before: topple an entrenched regime from a dense urban environment with minimal loss of civilian life.
History and military strategists cite two basic methods for conquering a city: siege - cordoning off the city until its occupants capitulate - or direct assault. Over the weekend, the US began implementing classic elements of a siege. Each approach has its particular perils, and historically, both have caught local populations in the crossfire.
In the coming days, the battle for Baghdad will likely see US and Iraqi forces alike employ lessons of past street-level battles - from Hue, Vietnam, to Grozny, Chechnya. The US brings technological superiority to the fight. But unfamiliarity with Baghdad's nooks and crannies, and the possibility of chemical weapons being unleashed by a dying regime, may put the US low-casualty mission to the test.
Two and a half weeks of coalition airstrikes have weakened an already outmanned Iraqi Army. By positioning itself at key entry points, the US is attempting to asphyxiate the city, keeping supplies and fresh fighters from reinforcing the 60,000 Special Republican Guard troops, paramilitaries, intelligence agents, and foreign volunteer fighters that have reportedly melted into the city's neighborhoods.
The 1st Marine Division currently controls eastern entry points into Baghdad, the Army's 3rd Infantry division controls the southwest, and the 101st Airborne the west. Tens of thousands of US troops are currently in position, with more on the way. The US will use the airport as a staging ground for helicopters and warplanes that can provide close air support to ground troops.
An important objective will be gaining control of the city's information flow - broadcasting on radio and TV and even sending faxes and making calls to individual cellphones - in order to regulate what those both inside and outside Baghdad hear about events.
The ultimate goal of this choke hold, says retired Army Gen. Robert Scales, is to so weaken Saddam Hussein's regime that it will collapse on itself. "You take your time to slowly close the noose," says General Scales. "The last thing you want to do is corner someone. If you corner someone, they fight more ferociously."
This collapse would keep the US troops from having to do what few soldiers relish: toe-to-toe fighting within a maze of streets, alleys, tunnels, and high-rises. Marines operating near the city have already fixed bayonets at the end of their rifles in preparation for such combat.
In tight quarters, civilians and combatants can become indistinguishable. Gunfire can be launched at US tanks from rooftops and darting pickup trucks. And dense smoke billowing from flaming oil-filled trenches may only add to the confusion.
Familiarity with the urban terrain can often give locals an advantage, even when they are outgunned. To repel stronger Russian forces in 1995, rebels in Grozy, Chechnya, broke into small units of eight to 12 men armed with rocket launchers, automatic weapons, and Motorola hand radios. They repositioned street signs and booby-trapped doorways, sewer entrances, and even dead soldiers.
Eight hundred of the first 1,000 Russian troops to enter the city were killed, and nearly all of the 150 tanks and armored vehicles were destroyed. In response, over the next three weeks, the Russians counterattacked day and night, firing as many as 4,000 artillery rounds per hour, leveling the city.
A siege seeks to avoid this kind of combat. In 1982, in an effort to root out terrorists from the Palestine Liberation Organization (PLO), Israel blockaded Beirut, Lebanon, and encouraged civilians to leave. The siege lasted two months during which PLO targets were hit with artillery strikes. Israeli forces didn't move in until the PLO evacuated and the city was surrendered. While Israelis suffered relative low casualties, the destruction of the city was significant and civilian deaths substantial from the bombardment.
The difference this time is that the Bush administration is trying to limit the num- ber of civilian deaths and to do minimal damage to Baghdad's infrastructure. Civilians will be permitted to leave, although the US military is not encouraging them because of the potential for a massive humanitarian crisis at refugee camps. But fewer civilians in Baghdad would make it easier to target enemy combatants.
"If you drain the pond of water, the fish are easier to find," says General Scales.
Throughout this "loose" cordon, US probes will intermittently enter the city, as occurred Sunday with a column of armored vehicles, to measure resistance and remind residents and fighters of their presence.
Other pinpoint strikes will target key nodes of power: utilities and communication centers, bridges and airports, and political and military buildings. With so much of the Iraqi government's infrastructure already destroyed by airstrikes, the focus of precision raids may turn to mobile targets like vans that could be used to command troops or transport chemical weapons.
Special Operations troops and CIA operatives could encourage insurrection in Shiite neighborhoods. Unmanned reconnaissance drones will circle overhead while troops on the ground consult blueprints of Baghdad buildings reportedly obtained from foreign construction firms.
In theory, a cordon should limit civilian casualties since large numbers of American troops would not fight intensely inside the city. Realistically, though, civilians would probably bear the brunt of the hardships.
In the southern city of Basra, which has been surrounded by British forces for a week, Iraqis loyal to the Hussein regime have intimidated or even killed citizens who attempted to surrender or act sympathetically toward coalition troops. Loyalists are not likely to allow civilians to flee toward safety and may even use them as human shields. And crucial supplies are likely to become scarce quickly.
"If you apply pressure with the regime we're facing, the civilian population hurts," says David Dilegge, a consultant to the Marine Corps war-fighting lab. "They will not have food, water, and medical attention. That could be a public-relations disaster."
US military officials stress they would attack inside Baghdad directly only as a last resort. But if a cordon drags on too long, US forces may have little choice but to fight their way inside.
Such an assault will rely heavily on hundreds of teams comprising a dozen infantrymen and a tank. A tank's heavy machine guns can protect soldiers against ambushes. Infantry can guard tanks from rocket-propelled grenades fired from rooftops or basements.
Other ground troops may be inserted by helicopters into parks or stadiums, though antiaircraft fire makes that a more dangerous entryway.
Those troops who do secure individual buildings won't exactly knock on front doors, which could be booby-trapped. The US may turn to the experience of Israeli soldiers in the West Bank city of Jenin, says Martin Van Creveld, a professor at Hebrew University who briefed US Marine Corps officers last fall.
Where narrow alleys prevented Israeli tanks from advancing, infantrymen backed by helicopter gunships made their way forward house by house, blowing holes through inner walls instead of exposing themselves to dangerous streets. The US has reportedly purchased several armored bulldozers from Israel that can cut wide swaths through alleys and clear the way for tanks.
Good intelligence will be vital, says Randolph Gangle, a retired Marine Corps colonel who heads its Center for Emerging Threats and Opportunities in Quantico, Va. Sensors that help locate tanks can't differentiate between a soldier with a rifle and a mother cooking dinner.
The US military has little recent experience in directly assaulting cities, analysts say. Large numbers of American troops last faced off against an organized opponent inside a city during the Vietnam War in the city of Hue.
During that battle, Marines successfully drove out a far larger enemy force during the 3-1/2-week battle. But much of a seven-block battle area was destroyed and both civilian and US casualty rates during the battle were high.
Since then, US troops learned firsthand the risks inside cities during peacekeeping operations in Beirut, where a truck bomb blew up a Marine Corps barracks, killing 241; and Mogadishu where militiamen shot down two Black Hawk helicopters with rocket-propelled grenades. Estimates of potential American casualties in the Baghdad fight vary widely, topping out in the low thousands.
Iraqi troops are drawing on the experience of Somali "technicals," who battled American troops in Mogadishu, and the Chechen rebels in Grozny.
And Russian military experts have reportedly been advising Iraqis on how to conduct urban warfare. Ongoing guerrilla and terrorist attacks will also be a concern for US forces.
American troops are far better trained and equipped than the Russian Army in Chechnya. And Baghdad, a flat open city with few natural citadels, is an easier city to attack than defend. Few buildings in the Iraqi capital rise above three stories. Many of the taller ones have already been leveled or damaged by American bombs, and Baghdad's wide boulevards are harder to block with debris.
City landscapes thwart some American technological advantages. Buildings block radio transmissions and signals from global positioning satellites, and unlike in the open desert, US ground forces can't fire at targets from a safe distance.
However superior air and tank power, night-vision goggles, and body armor that can stop most bullets give US troops a decided advantage.
Still, there aren't enough soldiers in the entire US military to secure a city the size of Baghdad room by room.
"You have to divide and decide what you're really after," says Gideon Avidor, a retired Israeli Defense Force general.