One week into the conflict, Saddam Hussein's government has yet to fight back from the sky.
U.S. and British aircraft swarmed in the sand-stung skies over Iraq for more than a thousand times Thursday, hammering troops loyal to Saddam Hussein long before American ground forces will see them face-to-face near Baghdad.
The well-oiled ritual, used in Basra and An Nasiriyah, brings out helicopters, jets and even lumbering "Warthog" planes to knock out tanks, deflect artillery fire or rain down missiles from above.
"If a particular unit gets overmatched, gets isolated, close air support can come in, rebalance the playing field, provide the additional firepower and get those forces out of trouble," said Michele Flournoy, a defense policy expert at the Center for Strategic and International Studies.
The U.S. goal is to severely damage ground forces before American soldiers get close enough for a firefight. Tactics during the first Gulf War called for Iraqi forces to be degraded by 50 percent or more from the air before American ground troops engaged them.
Sandstorms that had grounded most aircraft subsided Thursday, and air support units went back to business. Coalition aircraft flew about 1,500 missions, roughly two-thirds of them close air support of U.S. troops, a military official said. Five hundred were strike flights on 200 pre-planned targets.
At dawn near Karbala, soldiers from A Company, 3rd Battalion, 7th Infantry Regiment watched Warthogs dive in to help a nearby unit fend off four armored Iraqi vehicles in the distance.
There was a blaze of Gatling gunfire, and missiles. Soldiers who awakened to the sounds of war in the desert were cheering on six miles away. "Did you see that fireball?" exclaimed Spc. Dean Bryant of Oklahoma City.
But the very nature of close air support also makes it dangerous work. An outmatched adversary may use surface-to-air missiles or chemical weapons - an option Saddam is said to be contemplating now.
Hovering above means that the aircraft can be hit by ground fire. Pilots and crew can be killed, wounded, captured. Such was the case earlier this week when an Apache helicopter went down in central Iraq and its two pilots were taken prisoner.
In the 1991 Persian Gulf War, much of the close air support came from the Air Force A-10 Thunderbolt, a low, slow, clumsy-looking jet - hence the nickname "Warthog." It was designed to destroy tanks, and has reinforced systems that make it difficult to shoot down.
The Apache helicopter is much more nimble than the Warthog. U.S. forces use it to sneak up on other troops at night and dump Hellfire missiles and small rockets on them. Equipped with radar, infrared and other sensors, Apaches can hit their targets from miles away.
Another major advance that Pentagon officials frequently tout is the use of precision-guided bombs to provide support from high-flying aircraft like B-52 Stratofortress bombers. Heavy bombers dropping satellite-guided bombs can hit stationary targets or large troop concentrations - a tactic used frequently in Afghanistan.
Close air support began a speedy evolution after the Vietnam War, when the Army wanted to shore up its ground forces from the air, said Rand defense policy analyst Bruce Don. At the time, guns were added to helicopters to help fend off hostile fire; the first generation of attack helicopters, the Cobra, developed from that.
"They can essentially hang around the battlefield and wait for the situation to develop until the forces need their gunfire," Don said. "There's hardly a country in the world that has this kind of capability. It really outmatches a lot of forces."
By Sonya Ross and Chris Tomlinson