The first stage of the ground campaign opened with American howitzers and multiple launch rocket systems firing at Iraqi troops.
Reporters traveling with the 1st Marine Division into Iraq saw burning oil wells that sent a black cloud into the night sky under a nearly full moon.
Under the shelter of night, and with the support of heavy bombing, the 1st Marine Division entered Iraq at around 9 p.m. local time. The U.S. Marines encountered some resistance from "rear guard" units; they opened fire with machine guns on an Iraqi T-55 tank and finally destroyed it with a Javelin, a portable anti-tank missile.
There were no American casualties.
There were no immediate details on the size and makeup of the entering force, or the location of incursion.
CBS National Security Correspondent David Martin reports the ground campaign has now been put in front of the air campaign.
"It is so clear that the Iraqi defenses are so soft," reports Martin. "The ground campaign is almost in full tilt.
"They are preparing the battlefield, getting rid of the obstacles."
Martin reports the change of strategy is partly being done to get the oil fields under control.
CBS News Correspondent Jim Axelrod reports the U.S. 3rd Infantry Division crossed the border into Iraq after unleashing ferocious artillery attacks across the frontier.
Maj. Gen. Bufourd Blount, the 3rd's division commander, had said the artillery barrage would signal the first phase of the ground war against Iraq.
The first report of allied troops crossing into Iraq involved British Royal Marine commandos, who launched an aerial and amphibious assault on an Iraqi peninsula.
The report by a Times of London correspondent said hundreds of British marines swept into the Al Faw peninsula. Before that, Royal Marine snipers and U.S. Navy SEAL teams harassed Iraqi positions, the Times said.
Britain's Ministry of Defense would not comment on the Times pool report, telling The Associated Press there was a "news blackout." Earlier, Gulf and Western news agencies also said coalition forces crossed into Iraq, but the reports could not be independently confirmed.
A second round of U.S.-led air attacks was launched Thursday night in Baghdad, but U.S. military officials said the assault was not the beginning of the massive air campaign the Pentagon has planned.
The air attacks underway in Baghdad were sea-launched Tomahawk cruise missiles fired at Special Republican Guard strongholds in Baghdad, according to two senior defense officials with direct knowledge of the operation, who asked not to be identified.
Two of the officials said Thursday's strikes involved a smaller number of Tomahawks than Wednesday's opening volley, which numbered approximately 40.
The U.S. cruise missiles hit the center of Baghdad, reports CBS News Anchor Dan Rather.
"They shook the city like a series of small earthquakes," says Rather.
Eyewitnesses in Baghdad point out that plumes of smoke rose from the vicinity of the foreign ministry and the planning ministry after the missile strikes.
White light glowed in the sky as dozens of artillery shells were fired. Infantrymen who were between the howitzers and the Iraqi border cheered as the shells screamed overhead.
The ground war was launched about an hour after U.S. Defense Secretary Donald Rumsfeld promised in Washington: "the days of the Saddam Hussein regime are numbered."
Rumsfeld said the United States had hit a senior Iraqi leadership position in its initial strikes on Baghdad Wednesday night. He offered no details, saying a damage assessment was pending.
The Pentagon assessed the damage Thursday from its initial strikes against targets in Iraq and primed for a broader assault involving 250,000 U.S. and coalition forces.
The war's opening salvos were aimed directly at Iraq's leaders, including Saddam.
Commanders relied on more than 40 cruise missiles launched from Navy ships and submarines in the Gulf and the Red Sea, and 2,000-pound precision-guided bombs dropped by Air Force stealth fighter jets, military officials said.
A senior military official, speaking on condition of anonymity, said military intelligence was picking up signs and "circumstantial evidence" that Saddam and his senior leadership were either incapacitated or out of communication with battlefield commanders. It was too early to say if they were killed or wounded.
"We are seeing no coordinated response to our first attack," the official said. "It's little things here and there. Some individual commanders are hunkering down while others are launching small attacks and setting fires."
Military officials "believe it is significant that there is a lack of coordination and significant resistance to what we did," the official added.
Rumsfeld was asked whether military planners knew Saddam's location Wednesday night.
"We had what I would characterize as very good intelligence that it was a senior Iraqi leadership compound. We do not know what the battle damage assessment," will be.
The Kuwait News Agency, quoting an unidentified Kuwaiti Army source, said Thursday American and British troops had captured the southern Iraqi city of Umm Qasr and hundreds of Iraqi soldiers had surrendered.
But Iraq's Al-Shabab TV denied that Umm Qasr was captured, saying Iraqi and allied forces exchanged artillery and rocket fire across the Kuwaiti border. It quoted the official Iraqi News Agency.
Rumsfeld warned Iraqis not to go to work, but to stay in their homes and listen to coalition radio broadcasts.
"The day of your liberation may soon be at hand," Rumsfeld said. "The days of the Saddam Hussein regime are numbered. We continue to feel there is no need for a broader conflict if the Iraqi leaders act to save themselves and to prevent such further conflict."
Joint Chiefs of Staff Chairman Gen. Richard Myers warned that the war may not be easy.
"We do not regard combat as an easy task," Myers said at the Pentagon. "Warfare is dangerous. We will have casualties."
A helicopter carrying U.S. special forces crashed inside southern Iraq hours before the missile strikes Wednesday night, a senior defense official said. There were no casualties and the troops on board were all taken out safely, said the official, who spoke on condition of anonymity.
The official said the military was taking steps to destroy the helicopter rather than let it fall into Iraqi hands.
The incident makes clear the Pentagon was using a well-worn war tactic of dropping special commando forces behind enemy lines before the opening of the rest of the campaign.
Officials declined to say exactly where the crash occurred. But a widely discussed part of the war plan has been to send special forces into the country to secure oil wells, suspected chemical weapons sites and other strategic locations — as well as to search out Iraqi leadership.
The defense official also said a small plane headed from Iraq toward a Marine expeditionary force position in Kuwait but crashed short of its mark. The Marines donned gas masks because of fears that the plane could have been carrying chemical weapons, the official said. No agents were detected.