The Iraqi Republican Guard controls the bulk of Iraq's chemical weaponry, most of which can be fired from artillery guns or short-range rocket launchers, according to U.S. officials.
Word of the chemical threat came as U.S.-led forces clashed with the elite Guard fighters for the first time about 50 miles south of Baghdad. U.S. Apache helicopters fired on the guard to soften them up for ground forces heading north to Baghdad. The helicopters destroyed about 10 Iraqi tanks before ending their aerial attack.
Maj. Gen. Stanley McChrystal, the vice chief of operations on the Pentagon's Joint Staff, said the helicopter attacks followed military doctrine — combining deep strikes with psychological operations and, soon, artillery fire — to weaken the Republican Guard division before the U.S. 3rd Infantry Division hits it full force.
The Pentagon confirmed that one of the attacking Apache helicopters went down. Its two-man crew was later seen on Iraqi television, where they did not speak to the camera and appeared confused. The Pentagon identified them as Ronald D. Young Jr., 26, and David S. Williams, 30, both based at Fort Hood, Texas. They join five other U.S. POWs captured two days ago.
There were signs of artillery assaults on Republican Guard divisions Tuesday.
The first time U.S. troops would cross the "red line" would be in Karbala, a central Iraqi town that the invasion force is fast approaching.
The chances for a decisive battle for Baghdad hinge on whether or not the Republican Guards decide to fight. As of Tuesday, it didn't appear they planned to surrender.
If the battle takes place, analysts are split over whether and when Iraq might use chemical weapons.
Officers in the field might be reluctant to do so because if they lost the war and were caught, the consequences would be dire.
At the same time, if commanders felt their fate was sealed no matter what weapons they used, they would lose nothing by deploying chemical weapons.
There are also practical considerations: Have coalition air strikes already eliminated stockpiles, or the means to deliver them? And does Iraq even have such weapons?
CBS analyst Stephen Black, a former U.N. weapons inspector, said the most likely agents used would be either mustard gas, which burns the skin, eyes and lungs or nerve agents which leaves victims unable to breathe. They most likely would be delivered by ballistic missiles.
Such attacks are likely to be localized, rather than causing massive damage, Black said. "The damage plume for these things is not enormous – a few hundred yards so so," he said.
As for the protection gear the U. S. forces have, Black says, it should protect soldiers very well and allow them to operate in a chemical environment. "The problem will be moving about in those suits," he said.
U.S. forces have found evidence that Iraqi troops have gas masks and other protection against a chemical attack. Those who are totally unprotected, Black said, are the Iraqi civilians in the area
Iraq has denied it possesses or plans to produce any illegal weapons, whether chemical toxins, biological agents, nuclear weapons, or missiles with ranges in excess of the 93-mile limit imposed on the regime after the Gulf war.
In four months of work, United Nations inspectors found no definitive evidence that Iraq had chemical or biological weapons, but also saw no solid signs that the Iraqis had destroyed stockpiles they were known to have earlier.
The inspectors say they found no evidence of nuclear development. They determined that one type of Iraqi missile broke range limits; Iraq had destroyed about half of its reported stockpile of those Al Samoud 2 missiles when the war began.
But the United States alleged that Iraq was hiding illegal weapons and deceiving inspectors. Hunting these stockpiles down is considered the second priority of the war; the first is unseating Saddam Hussein's regime.
But so far, coalition troops have found no evidence of chemical or biological weapons. On Monday, U.S. troops used sophisticated detection equipment to search a munitions depot near An-Najaf, which an Iraqi captive suggested might be a chemical weapons site. The results of those tests were unknown.
The Iraqis have not used chemical or biological weapons in the field, to date.
At a briefing Monday, McChrystal said no evidence had been found of any illegal Scud missiles or launchers for them, and according to the U.S. military, no Scuds have been launched. Kuwait says two Scuds have been fired in its direction.