Updated

U.S. troops advanced through the deserts of southern Iraq in armored convoys Friday after launching the war's ground assault, meeting resistance from Iraqi forces in some areas and soldiers surrendering in others.

As the U.S. Marines and Army drove deeper into southern Iraq, British troops moved 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 targeted Iraqi positions in al-Faw, and witnesses in northern Kuwait side said they could hear thunderous explosions from the Umm Qasr area.

Further west along the border, some 200 Iraqi soldiers surrendered to the U.S. 15th Marine Expeditionary Unit just over an hour after it crossed the border into Iraq from northern Kuwait.

One group of 40 Iraqis marched in formation down a two-lane road toward the Americans and gave up. They were told to lie face down on the ground and were searched by the Marines. At the same time, Marines cleared bunkers, emerging from one with two Iraqis with bound wrists. One had a dark gray uniform, the other was barefoot. Abandoned weapons mortars were spread over a large area.

Elsewhere, U.S. troops met resistance from Iraqi units. The 7th Marine Infantry's 3rd Batallion apparently had to delay its foray into Iraq after -- according to military radios -- a large number of previously unknown tanks was sighted on the Iraqi side of the border.

The unit took small arms and artillery fire Thursday night, and at one point a U.S. Cobra helicopter accidentally fired a missile at a U.S. M1 Abrams tank, injuring one soldier and forcing abandonment of the smoldering tank. Friday morning, the unit opened a massive artillery barrage across the border.

In Iraq, Marines in the 1st Division 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 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.

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.

The start of the advance into Iraq was signalled Thursday night by a thunderous artillery barrage by allied forces in northern Kuwait across the border. Infantrymen on the move, their weeks of waiting at an end, cheered as shells screamed overhead.

The armored vehicles of the 1st Marine Division rolled across the border at around 9 p.m. local time (1 p.m. EST). As they moved through the desert, burning oil wells were visible, spewing black smoke into skies lit by a nearly full moon.

Earlier Thursday, 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.

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

Forces continued to mass near the border in northern Kuwait in the morning Friday, preparing to follow into Iraq. The 101st Airborne Division's 3rd Brigade pulled up to a tactical staging area.

"We're poised to do what the 101st does best, air assault," the brigade's commander, Col. Michael Linnington, said.

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.

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.

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.

In the opening barrage Thursday, the 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.

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.