SOUTHERN IRAQ -- The U.S. Marines and Army rolled into Iraq and engaged Saddam Hussein's forces in the desert on Thursday, joining British troops in launching the war's ground assault.

As U.S. armor drove deeper into Iraq early today, British troops conducted an assault on the strategic al-Faw peninsula, Iraq's access point to the Persian Gulf and the site of major oil facilities. British military officials said they hoped to seize the key port of Umm Qasr before the day's end.

Through the night and as the sun rose, artillery barrages lit up the sky, and witnesses in northern Kuwait side said they could hear thunderous explosions from the Umm Qasr area.

Thursday evening, U.S. forces in northern Kuwait signaled the start of their advance on Iraq with a thundering artillery barrage over the border. Infantrymen on the move, their weeks of waiting at an end, cheered as shells screamed overhead.

Under the shelter of night and supported by heavy bombing, the armored vehicles of the 1st Marine Division rolled into southern Iraq at around 9 p.m. local time (12 p.m. CST). As they moved through the desert, burning oil wells were visible, spewing black smoke.

Light resistance

The 20,000 Marines met light resistance from Iraqi "rear guard" units. They opened fire with machine guns on an Iraqi T-55 tank and destroyed it with a Javelin, a portable anti-tank missile.

Troops from the Army's 3rd Infantry Division also crossed into Iraq and came into contact with several Iraqi armored personnel carriers, destroying at least three of them, front line troops reported by radio.

There were no reports of U.S. casualties in the engagements. In northern Kuwait, a helicopter crashed Thursday, killing the four American crewmembers and 12 British troops on board.

Thursday evening, elite British troops were dropped by Chinook and Sea Stallion helicopters to seize oil facilities in al-Faw after U.S. Seals prepared the area, according to Britain's Press Association news agency.

By taking southern Iraq, the allies would command access to the Gulf and set the stage for the first major conquest on the way to Baghdad -- Basra, Iraq's second largest city, just 20 miles from the Kuwait border.

The move on the area between Basra and the Persian Gulf suggested that the allied strategy on the ground calls for a two-pronged attack -- one to clear Iraqi resistance in the southern oil region while the other charges north toward Baghdad.

Australian troops were also in Iraq identifying targets for coalition aircraft and monitoring Iraqi troop movements, an Australian defense force spokesman said.

"Things are going very well," said Defense Secretary Donald H. Rumsfeld, in Washington.

Yet conditions were sometimes difficult. The Marines drove through thick, swirling dust storms. Troops detected Iraqi tanks and armored vehicles hidden behind sand berms by the heat they gave off, and U.S. aircraft attacked the positions.

None of the forces apparently encountered chemical or biological weapons. The Marines passed burning oil wells, though it was not known who had set them afire. Flames shot up hundreds of feet, thickening the air with black smoke.

Artillery, mortars and howitzers rumbled for hours in the nearly deserted far north of Kuwait, mixed with bursts of rocket launchers. The explosions rattled tin roofs noisily on their wood frames miles away and shook concrete houses.

The attack came at the end of a day that began with allied troops at the other end of the gun barrel, as Iraq -- responding to the American bombardment of Baghdad and other targets -- launched missiles into Kuwait, where allied forces were primed to attack.

The Iraqi military claimed in a statement it had repulsed an "enemy" attack at Al-Anbar province, on Iraq's border with Jordan and Saudi Arabia. It was not clear what force could be attacking from that point, and the statement did not mention attacks in the south.

Meanwhile, the U.S. 3rd Infantry Division's artillery opened fire on Iraq with Paladin self-propelled howitzers and multiple launch rocket systems. More than 100 artillery shells were fired toward southern Iraq in a five-minute barrage. White light glowed in the sky above the cannons, as explosions were heard from Iraq.

No fire was returned, but the shooting was unnerving to those within earshot. Pakistani and Indian farm workers ran out in their yards in the dark, shouting. "Give me my passport," one field worker told his foreman.

"The Americans are bombing to the left of us, to the right of us, the front, the backside, and I'm under it!" the foreman said later.

Under a bright moon late Thursday, troops had streamed toward the border in convoys of trucks, tankers, humvees and other military vehicles of the 101st Airborne Division.

As the convoy moved at a steady 30 mph clip, troops pulled scarves across their faces as huge clouds of dust rose from the flat desert. Pairs of red tail lights and yellow headlights strung across the desert, filtered by a fog of dust.

Earlier in the day, the waiting troops had their first brush with action when Iraq fired missiles into Kuwait. There were cries of "gas, gas, gas," and U.S. troops ran for their protective suits and gas masks -- but authorities said none of the missiles carried biological or chemical payloads.

Soldiers of A Company, 3rd Battalion, 7th Infantry Regiment were eating lunch when an Iraqi missile hit the desert. They wore the masks for 20 minutes until given the all-clear.

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

"I think it's 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."

Some Marines were simply excited to begin fighting, something they had trained to do for years, and occasional screams of "Let's get it on!" came from some of their weapons holes.