As CBS News Correspondent Rita Braver reports, U.S. troops have been trained extensively to deal with many potential scenarios.
Scenes of U.S. troops scrambling into protective gear as Iraqi missiles scream overhead are proof of the constant fear that haunts this military operation, that the Iraqis might launch chemical or biological weapons.
Even as the U.S. seems to be winning the war, there are new reports that Saddam has authorized local commanders to use chemical weapons. Defense Secretary Donald Rumsfeld is warning, "To those in the Iraqi regime chain of command, some words of advice: Do not obey regime orders to use weapons of mass destruction."
Brigadier Gen. Steve Reeves says the U.S. has spent 1 billion dollars a year since 1994 on protection and detection gear.
"This is the world's first stand-off chemical agent detector. This one will detect a chemical vapor out to 5 kilometers away. That's clearly very important," he says.
Each platoon also gets its own chemical agent alarm.
"It detects simultaneously against both nerve agents, like VX, or blister agents, like mustard, so that you get the earliest possible warning and it's very, very sensitive," Reeves says.
"In the event that you are, in fact, contaminated with a nerve agent, everyone carries an antidote treatment kit," he continues and demonstrates by pretending to inject his leg with the serum, which would counter the effects of the nerve gas.
There are field units to check de-contamination, Quick Test kits to check for biological agents like anthrax, and - though Saddam is not believed to have nuclear weapons - a new generation of radiation detectors
All of this is because officials know Saddam has used chemical weapons many times before, causing more than 40,000 Iranian casualties during the Iran-Iraq war and killing more than 5,000 of his own people in Kurdish areas of Iraq.
Holding her album of pictures, Dr. Katrin Michael recalls June 5, 1987. "We were just waiting to have our dinner," she says, when Saddam Hussein dropped bombs filled with cyanide and mustard gas on her Kurdish resistance unit. Within a few hours, she had gone blind, as had a close friend.
"And he asked me, 'Are you blinded, too?' I said, 'Yes, I have, I'm blind.' And he told me, he started asking me, 'Is everybody blind?' I said, 'No, some of us not still blind, some of our friends…'" she breaks down crying and cannot finish telling her story.
Michael regained her sight after three days, but still has permanent problems breathing. Her friend died.
It is stories like hers, told to President Bush just last week, that helped convince Mr. Bush that Saddam Hussein might actually use weapons of mass destruction again, even though he did not employ them in the first Gulf War.
Even the United Nations inspectors, who destroyed thousands of chemical and biological weapons and who up until a few days ago were asking for time to search for more, admit that they have no way of knowing Iraq's capabilities.
"You just don't know what's there," says Ewan Buchanan, a spokesman for the U.N. weapons inspectors. "I mean Iraq declared that it had produced 8.5 thousand liters of anthrax. But there are questions as to whether or not Iraq could have indeed made three times as much as they actually declared. So there was a potential of Iraq having produced at least 25,000 liters of anthrax. And that's quite a staggering amount."
Or think about VX nerve gas, Iraq claims it made and later destroyed 3.9 tons of the lethal material. "But the problem for us is we cannot quantify how much was actually dumped there," says Buchanan. "And yes, it is possible to calculate that Iraq had the capability to at least have made much more than 3.9 tons."
There are tons of other substances that U.N. inspectors could never account for: more biological agents that can cause internal hemorrhaging and slow death, other types of nerve and mustard gas.
And, the irony of all this is that the United States supplied much of the technology that helped Saddam create his weapons of mass destruction.
Miriam Rajkumar, co-author of "Deadly Arsensals," a book that investigates the spread of nuclear, biological and chemical weapons around the world, says, the U.S. and Iraq were allies in the 1980s, fighting a war against the revolutionary regime in Iran.
"But this was a different time, it was a different time," she says.
Today, the Bush administration is urgently trying to find and secure hidden stockpiles of dangerous material in Iraq.
Special teams of military and intelligence operatives, many who've gone through the military's chemical weapons training school at Fort Leonard Wood, Mo., will be combing the Iraqi countryside for secret storehouses.
Maj. Gen. John Doesburg, who runs the Army's biological and chemical defense command, says, "You want to ensure that there aren't any terrorist groups who are out there who also have been able to identify potential sites and now going in saying, 'OK, I want these and I'm going to take these for my needs.'"
And there is added pressure for the U.S. to turn up those weapons that UN inspectors could not find. After all, says Rajkumar, that is the "stated reason" for this war. "Otherwise, people are going to wonder what the real justification of this war is."
Asked whether there is a chance there is nothing to find, Gen. Doesburg says, "I personally think that the chances are high that we're going to find something. At this point we should not breathe a sigh of relief, even though Saddam has not used any of these weapons so far."
That doesn't mean that they couldn't be used in the future. He says, "If they're not used in the opening days, we still have to have to be concerned that he could potentially use them at any time during the conflict."