Sandstorms slowed Baghdad-bound troops on Tuesday, grounded scores of aircraft and blinded the array of electronic eyes needed not only to target and attack Iraq, but to separate friend from foe.

Freak thunderstorms also thwarted badly needed humanitarian aid to the country's sick and starving.

War's most volatile variable — bad weather — was gumming up guns, breaking down engines and generally slowing a military campaign built for speed, forcing the U.S.-led military to "re-choreograph" the assault on Saddam Hussein's regime, said former Gen. John Abrams, who commanded the U.S.-led deployment to Bosnia.

"If you show up with a force that doesn't have a broad suite of contingencies, you get stymied," Abrams said. "The question that comes up with this situation is: Does this force have the width of capabilities to compensate?"

Reports from throughout the theater showed nature playing the role of third combatant. In southern Iraq, the 101st Airborne Division was forced to halt its march north because attack aircraft couldn't see through the sand well enough to land at a pair of new forward fueling stations.

"It's very frustrating," said Lt. Col. Laura Richardson, a Black Hawk helicopter pilot and commander of the division's 5th Battalion, said as sandstorms gave way to downpours. "These things can come in so fast."

A severe sandstorm swept across Karbala — a stop on the road north to Baghdad — forcing most of the soldiers to take refuge inside their Bradley fighting vehicles. A few men fought the gusts and the sand wearing goggles, helmets and scarves wrapped around their faces in the 50 mph winds, scrambling to maintain their sandblasted vehicles for a march on Baghdad.

The weather also dealt a blow to relief efforts; thunderstorms lashed the Iraqi port of Umm Qasr, slowing efforts to get the captured, badly damaged port open to ships laden with water, medicine and other provisions.

A British vessel carrying 1.5 million bottles of water was waiting to anchor, while naval helicopters ferried smaller amounts of supplies. Relief groups fear a growing humanitarian crisis in Iraq because of water shortages and damage to sewage treatment plants, raising the prospect of widespread disease.

"It's vital we get the port open as soon as possible to get the aid flowing to the people who need it," said British Navy Lt. Col. Paul Ash.

The sandstorms affected operations at sea, disrupting combat flights Tuesday from two aircraft carriers in the Mediterranean. A dozen aircraft that took off from the USS Harry Truman returned a few hours later without reaching targets in northern Iraq. On the USS Theodore Roosevelt, war planes stayed put.

"Weather sometimes does slow things down, and in other cases provides cover and accelerates some things," said Rear Adm. John Stufflebeem, aboard the Truman.

Abrams said the sandstorm can indeed provide cover and allow troops to reposition themselves while moving in closer formation. U.S.-led troops were fairly dispersed to minimize the impact of an Iraqi chemical or biological weapon, he said.

Abrams commanded the 1996 NATO deployment to Bosnia, where fog kept aircraft from landing for six days. Yet that highly publicized delay worked as a distraction while the force quickly built a bridge across the Sava River to Bosnia — a span bigger than the Brooklyn Bridge — and unexpectedly secured the region with ground forces.

Tuesday's sandstorm posed a serious test for the trend to reconfigure the military to wage war with quickness, agility and minimal ground troops.

The dust likely interfered with infrared, laser and audio tracking of targets and the invasion force's own troops, sharply increasing the chances of friendly fire casualties, Abrams said.

Thermal sensors can detect heat through dust, but optical sensors cannot, he said, which means the military would probably have to double its human reconnaissance to minimize confusion and uncertainty. Commanders also have to move closer to the front of their units to get a better grasp on a situation, he said.

"It really slows the tempo of your operations down," he said. "It impacts on movement rates. It impacts on some of the technology, the weapons, whether artillery or machine guns. An engine that may take two or three hours to repair would take maybe a day to repair."

Storms were so heavy in Baghdad that it appeared darkness had fallen. Iraq often sees sandstorms in spring, but Tuesday's was exceptional, bringing dust and sand from as far away as Egypt and Libya, said AccuWeather meteorologist John Gresiak. Lighter winds were likely Wednesday, with no major sandstorms for at least several days.

"Now, when the weather clears, I think you'll see a return to a very rapid movement north," said Col. Michael Linnington, commander of the 101st's 3rd Brigade. "I think everybody knows the reason we're not attacking is we don't have the weather to fly."