The Marines needed a loudspeaker, a few warning shots and less than an hour this afternoon to seize what commanders called a "jewel in the crown" of their initial thrust into Iraq, a key facility in one of the world's richest oil fields.

The oil complex, the precise location of which commanders asked not to disclose, fell without a death on either side. On their first day in the war, troops from the 1st Marine Division faced sporadic small arms fire and took 25 to 30 prisoners of war and 34 civilian detainees.

"I'm absolutely overjoyed because I have the same number of Marines I started with, everyone's in one piece and the objective has been achieved," said Lt. Col. Christopher Conlin, commander of the 1st Battalion, 7th Marine Regiment. "This was the main objective for this portion of the ground war."

The Rumaila oil field, about 20 miles west of the city of Basra, is one of the most important in Iraq and holds 14 percent of the world's known reserves. U.S. officials feared that the Iraqis would sabotage oil facilities to slow the U.S. advance and complicate plans to rebuild the country under postwar occupation.

More than 1,100 Marines raced in broad daylight north to the oil complex from their camp in Kuwait. They were clad in cumbersome chemical suits and rubber boots and traveled in "Amtrak" Amphibious Assault Vehicles, Humvees, and a few seven-ton trucks. The ride was rough at times, with upwards of 22 combat-laden Marines packed into the Amtrak's rear compartment, roughly the size of a large cargo van. Progress was slow for most of the day, as hundreds of vehicles passed through a breach in the border that was only a few lanes wide.

Once in Iraq, the convoy traversed a countryside of rundown buildings, stone houses set on small farm plots and the charred remnants of Iraqi military vehicles, some of which had been destroyed earlier in the day by the 1st Marine Tank Battalion and the 3rd Battalion, 7th Marine Regiment. In the Iraqi town of Safwan, some residents ran alongside the vehicles waving white flags, while others stood impassively by the side of the road, watching the procession.

With two Marines killed in combat elsewhere in southern Iraq today, the fighting showed many Marines that the Iraqi army would not lay down before them, as some analysts had predicted. "We had heard they may not fight back, but it looks like they already are," said Sgt. Aloysius Donovan, 23, of Sault Ste. Marie, Mich., as he watched a massive bombardment of Safwan Hill, a listening post in southern Iraq. "We'll be ready if they want to fight us."

When they reached the oil facility, the Marines advanced on foot or by crawling on their hands and knees. For months, rumors had circulated that besieged Iraqi forces might sabotage the nation's oil infrastructure as they had done in Kuwait during the 1991 Persian Gulf War. Today, advance teams of special operations forces found no evidence of explosives or booby traps in the facility, an assessment that was later confirmed by a more thorough search.

"If the place had blown with the Marines in there, that could have been a disaster," said Conlin. "The place is still a target and we will do everything we can to keep it safe. This oil is what the country will use to rebuild after the war, which is why we had to prevent it from being destroyed."

Most of the complex was secured in a matter of minutes, after Marines used a loudspeaker to urge surrender. Some of the workers encountered at the facility were carrying leaflets in Arabic dropped by U.S. forces in recent days saying that they would not be harmed if they cooperated. Radio broadcasts also encouraged compliance.

"We're here to help the battalion commander communicate with foreign audiences," said Capt. Matt Gebhard, a psychological operations officer from Pittsburgh. "It's going great so far."

The Marines seizing the complex did encounter some mild resistance. One security guard threw a bag on the ground and began to run when approached by Marines. He was shot in the arm. Later, a prisoner tried to escape, but surrendered again when a Marine guarding the facility fired a warning shot and then shot the vehicle the escapee was attempting to enter.

Civilians who surrendered peacefully were classified as detainees, and were slated to be released late this evening. Those who resisted, or those found with military items such as gas masks or Iraqi army identification cards, were tagged enemy prisoners of war. Interpreters and interrogation specialists questioned both groups.

At one stage, four Navy corpsmen traveling with the Marines attended to an injured child when the car he was traveling in passed down the road to the oil complex. "We gave [Iraqis] food and water if they asked for it, and some even gave us the thumbs-up," said Sgt. Eric Strause, 32, of San Antonio, Tex.

The Marines on the ground were supported by a heavy air presence as planes and Huey and Cobra helicopters swooped overhead throughout the day.

Before abandoning their camp in Kuwait, some Marines burned letters from home to cut down on weight in their packs. Intelligence officers disposed of their maps of training grounds in Kuwait. The morning that the move north was announced, a group of Marines packing their bags began singing "Start spreading the news, I'm leaving Kuwait."

But the wait would continue. When they got to the staging area, some 12 miles from the Iraq border, they spent several backbreaking hours digging "sustainability holes" designed to protect them from artillery or missile fire. Five Scud missile alerts sent Marines scurrying for their holes, gas masks on, sometimes for up to an hour until they got the all clear. After three relatively aimless days at the campsite, the frustration grew.

"The hardest part is not knowing when," said Matthew Funicello this morning, about a half-hour before the Marines were given the order to invade. "We know we're here for a reason and there'll be plenty to do when we do cross the line."

By this evening, many said they were glad their first taste of combat was a relatively bloodless success.

"If you can achieve the objective without having to shoot anybody, than that's about as good as it gets," said Sgt. Steven Christopher, 23, from Derry, N.H., who helped coordinate the processing of prisoners and detainees. "We got lucky 'cause no one was armed, and only a few fought back. It might not be that way next time."

U.S. Marines take cover from Iraqi fire as British artillery rounds explode in the early stages of the push into southern Iraq.U.S. Marines from the 15th Marine Expeditionary Unit take firing positions after hearing the sound of gunfire in southern Iraq. Hundreds of Iraqi troops surrendered to members of the unit.