Updated

U.S. troops got their first real scare Thursday when Iraqi missiles streaked across the border into Kuwait, forcing the Americans to climb into protective suits and put on gas masks.

The American military said it used Patriot missiles to shoot down at least one Iraq missile. In the Kuwaiti desert, an Iraqi missile flew overhead and landed harmlessly in the desert.

No injuries were reported, and there was no immediate evidence the missiles had chemical or biological warheads. It was not clear whether the Iraqi missiles were Scuds or Al Samoud 2s.

The Iraqi attack came several hours after the United States launched precision-guided bombs and more than 40 Tomahawk missiles in strikes it said were aimed at Saddam Hussein and his top leadership.

U.S. Army troops at Camp New Jersey in the Kuwaiti desert put on their chemical and biological protective gear in response to an alert caused by one of the missiles, but were given the all-clear a few minutes later.

The 1st Marine Expeditionary Force near the Iraqi border was on the highest alert level and were ordered into bunkers three times during the morning.

The Marines dropped food trays and ran out of showers to hastily don their gas masks and protective gear. Inside they bunker, they traded jokes.

"Did anybody take out insurance?" cracked one person, hidden by his mask.

At another, undisclosed position in the desert along the Iraqi border, the men of A Company, 3rd Battalion, 7th Infantry Regiment were eating lunch when the Iraqi missile hit the desert. The locomotive-like roar of the missile flying through the air followed the sound of impact because of the distances involved.

Within a minute, a flash message came across the radio, reporting that a tactical ballistic missile had landed in the desert, near U.S. troops. A few minutes later, all troops were ordered into protective clothing for chemical and biological warfare.

The men moved swiftly but calmly, systematically putting on their masks, then the clothing. Once one soldier was done, he would make sure another soldier had his gear on properly.

The still desert heat raised anxieties, since gas or vapor from biological and chemical weapons lingers in little or no wind, causing more damage. In heavy wind, the gas or vapor disperses quickly.

The men were quiet, since shouting to be heard from inside a gas mask takes extra breath. They were also listening for any more incoming missiles.

About 20 minutes later, the radio crackled, "All clear."

After removing his mask, company commander Capt. Chris Carter of Watkinsville, Ga., said: "Saddam is a fool."

"I think its an obvious attempt by Saddam Hussein to demoralize the army and the American public," Carter said. "An attempt that has been a miserable failure. He's probably got the guys more ready to fight than ever."

The men of the unit returned to cleaning their weapons and reading books, waiting for their part of the war to begin with a new awareness of the hazards ahead.

"I know what I'll be using as a pillow tonight," Staff Sgt. Bryce Ivings of Sarasota, Fla., said of his protective suit.

After weeks on standby in the Kuwaiti desert, U.S. troops appeared to welcome news that war was under way and were eager for orders to cross into Iraq.

"It's a relief we can finally go," said Spc. Robert McDougal, 21, of Paris, Texas, as the 101st Airborne broke camp Thursday. "Standing by is the hardest thing to do. It is time to put our training to the test."

Scores of vehicles, including bulldozers, Humvees and trucks full of equipment and supplies, lined up in Camp New Jersey, ready to move out. A dust storm that buffeted the troops on Wednesday had eased, giving way to a relatively cool morning in the low 80s with a few clouds.

Soldiers were up at dawn, cleaning tents and stuffing items into duffel bags. Some tried to slip out to the dining facility for one last hot meal before leaving.

Sgt. Brian McGough, 27, Philadelphia, sat by his automatic grenade launcher as he loaded rucksacks into storage containers.

"No one ever prays for war, but if it comes to that we are trained to do it," he said.

Elsewhere in Kuwait, members of the 709th Military Police Battalion learned about the strikes on Baghdad from a reporter.

"Good. At least we know what we will be doing in the next three days," said Lt. Col. Richard Vanderlinden, the battalion commander. He said his MPs would follow on the heels of advancing U.S. forces, dealing with prisoners of war and displaced Iraqi civilians.

Some Iraqi soldiers have surrendered already. An officer with the 3rd infantry Division, briefing reporters on condition on anonymity, said entire Iraqi divisions are expected to surrender swiftly.

Aboard the aircraft carrier USS Kitty Hawk in the Persian Gulf, ordnance crews in protective headgear and red life vests wheeled 500-, 1,000- and 2,000-pound bombs along the flight deck Thursday and fitted them under the wings of F-14 Tomcats and F/A-18 Hornets. The bombs, equipped with laser guidance systems, were marked with yellow stripes on their nose to indicate they were live munitions.

Military officials said the Tomahawk missiles fired at Baghdad in the opening salvo were launched from warships in the Red Sea and Persian Gulf -- the destroyers USS Milius and USS Donald Cook; the cruisers USS Bunker Hill and USS Cowpens; and the attack submarines USS Montpelier and USS Cheyenne.