One day into Operation Iraqi Freedom, U.S. Defense officials told Fox News Thursday night there are troops on the ground in the southern, western and northern regions of Iraq.

In a blow to coalition forces, a U.S. Marine helicopter crashed in Kuwait Thursday, killing all 16 American and British soldiers aboard, military officials said.

The crash of the CH-46 Sea Knight helicopter killed 12 U.S. and 4 British soldiers, officials said.

There is also a great deal of uncertainty on the fate of Saddam Hussein and his sons, who were believed to be in a complex that was struck during the opening barrage. There are reports that medical attention was called in after the strikes, but there is no confirmation of who it was for.

Throughout the day of fighting Thursday, coalition ground forces invaded Iraq swiftly from the South, missiles hit significant targets in Baghdad, and members of Saddam Hussein's elite Republican Guard started talking of surrender.

Senior military officials said Americans are involved in two-way communications -- some through back channels -- with Iraqi leaders. The talks are aimed at securing surrender or a coup, according to officials.

Defense Secretary Donald H. Rumsfeld said the communications included Iraq's elite Republican Guard and he was optimistic that it was still possible to oust Saddam without a massive U.S. attack.

"We still hope that it is possible that they [Iraqi leaders] will not be there without the full force and fury of a war," Rumsfeld said Thursday night after meeting with lawmakers. "There are communications in every conceivable mode and method, public and private."

The defense secretary said there was "broad and deep evidence that suggests that there are people going through that decision-making process throughout that country today."

Allied forces continued their attack on Baghdad Thursday, firing sea-launched Tomahawk missiles into the heart of the Iraqi capital. And U.S. Marines were on the move in the South, crossing over the border from Kuwait and heading north.

In a significant move, the Marines secured the Iraqi border town of Umm Qasr, the only major seaport for goods to enter Iraq.

Umm Qasr is 30 miles to the south of Basra, which coalition forces hope will be the first major Iraqi city to fall.

About an hour before dawn Friday, Reuters reported huge explosions outside Basra.

Defense officials told Fox News that troops were also on the ground in northern and western Iraq, but would not disclose their positions or exact mission.

Pentagon officials said large numbers of senior Republican Guard members are signalling that they would like to surrender.

"There are significant indications that the Iraqi military is breaking from within," a Defense official told Fox News. "So far, so very good."

In Baghdad, huge plumes of smoke could be seen from the west bank of the Tigris as missiles struck three distinct locations, including Saddam Hussein's main presidential palace and the ministry building. Senior Defense officials said the missile strikes were aimed at Republican Guard strongholds in the capital.

Iraqi radio reported that Saddam's family home had been bombed, but there were no casualties in the attack.

There were reports that a 10-story office building damaged in the attack belonged to Deputy Prime Minister Tariq Aziz, a powerful figure in Saddam's regime and a stalwart of his ruling Baath party who often speaks for the Iraqi leader.

The Iraqi military said four soldiers were killed and six others wounded in the day's strikes, during which it said a total 72 cruise missiles were fired. The morning wave of missiles killed one other person -- apparently a Jordanian civilian -- and injured 14, the International Red Cross confirmed.

While Baghdad was quiet for the rest of the night, explosions were heard before dawn outside the key northern city of Mosul, according to the Arab television station Al Jazeera.

Units of the U.S. Marine 1st Expeditionary Force crossed from Kuwait into southern Iraq to begin securing positions for a large-scale coalition invasion, and Fox News correspondent Rick Leventhal reported they were being fired upon by opposing troops.

An Associated Press reporter accompanying the Marines said he saw burning oil wells on his way into Iraq. He said the fires were "burning furiously" -- and sending up a cloud of black soot.

In the hours before crossing the border, the Marines put on their full chemical suits -- masks, gloves and full combat gear -- three times in less than two hours because of Iraqi missile launches into Kuwait.

British troops were also on the move. In an evening address, Prime Minister Tony Blair said British forces had joined the Americans in attacking Iraq "from air, land and sea."

"Their mission: to remove Saddam Hussein from power, and disarm Iraq of its weapons of mass destruction," he said.

Red and white tracers streaked across the night sky in Baghdad beginning several hours after sunset -- about 9 p.m. -- and the flash of explosions could be seen on the horizon.

Anti-aircraft fire was constant as the explosions rumbled in the distance.

F-14 and F-18 jets took off from the USS Theodore Roosevelt in the eastern Mediterranean, armed with missiles and bombs.

And the heaviest bombing is yet to come. U.S. officials say these air strikes are not the start of the massive "shock and awe" air assault that the Pentagon plans to unleash soon.

To the south, meanwhile, the ground war has begun.

The U.S. 3rd Infantry Division's artillery opened fire Thursday night on Iraqi troops in southern Iraq, using Paladin self-propelled howitzers and multiple launch rocket systems in the first stage of the major assault designed to topple Saddam and liberate Iraq.

GIs on the ground cheered as the sky lit up when cannons fired dozens of artillery shells, Fox News correspondent Greg Kelly reported. In the distance, explosions could be heard inside Iraq.

A large explosion was seen in Basra, which allied forces hope will be the first city to fall as they march toward Baghdad.

The Pentagon confirmed that Iraqi forces had set oil wells ablaze southwest of Basra. Rumsfeld, in an afternoon press briefing, said there were reports that "as many as three or four" oil wells were on fire.

In Kuwait City, people donned gas masks as air raid alarms sounded several times throughout the night. Sources told Fox News that an Iraqi Scud missile had landed in the Kuwaiti desert.

Baghdad, meanwhile, was hunkered down, bracing for the awesome assault that is certain to come. Air raid sirens blared intermittently in the night, and anti-aircraft fire lit up the sky.

The capital took its first strike before dawn Thursday, when the United States fired dozens of missiles at "targets of military opportunity."

A few hours after the strike, Iraq responded, sending what may have been Scud missiles toward allied troops stationed in Kuwait. There were reports that at least one was intercepted by American Patriot missiles.

Reports that Saddam was wounded in America's pre-dawn "decapitation" strike on Baghdad turned out to be false.

Rumsfeld, in a morning press briefing at the Pentagon, said the American missiles hit a senior Iraqi leadership position in the pre-dawn attack, and a damage assessment was pending.

The assault "was the first. It likely will not be the last .... The days of Saddam Hussein are numbered," Rumsfeld said.

He urged the Iraqi military to abandon their leader, and he issued this stern warning:

"If Saddam Hussein or his generals issue orders to use weapons of mass destruction, those orders should not be followed."

The "decapitation" attack targeted Saddam personally, and the barrage of cruise missiles and bombs was a prelude to a major invasion of Iraq.

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.

"We are seeing no coordinated response to our first attack," the official said. "It's little things here and there. Some individual commanders are hunking 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.

Iraqi Information Minister Mohammed Saeed al-Sahaf said one person died in the U.S. strikes and that several others were injured. He said the missiles hit a customs office and some empty Iraqi TV buildings, among other targets.

President Bush conferred with National Security Adviser Condoleezza Rice early Thursday on the initial strikes, as officials tried to determine whether the attack had succeeded.

Bush called his Cabinet to the White House for a mid-afternoon war update, a day after he told a global audience that war in Iraq "could be long and more difficult than some expected."

The first missiles hit targets in Baghdad shortly before dawn Thursday, less than two hours after Bush's deadline of 8 p.m. EST Wednesday for Saddam to yield power.

"These strikes are being characterized as a 'decapitation,' targeted at command and control nodes," U.S. spokesman Marine Colonel Chris Hughes told Reuters. "If successful, it will radically change the way we do things."

Bush, in an Oval Office address, announced to the nation that war had begun, stating that the barrage was the opening salvo in a "broad and concerted" operation to "disarm Iraq, to free its people and to defend the world from grave danger."

"I assure you this will not be a campaign of half-measures, and we will accept no outcome but victory," the president said.

Two hours after the cruise missiles hit, a subdued-looking Saddam appeared on Iraqi television in a military uniform and vowed an Iraqi victory.

Calling the attack on Baghdad a "shameful crime," Saddam said, "We promise you that Iraq, its leadership and its people will stand up to the evil invaders. They will face a bitter defeat, God willing."

U.S. officials were trying to determine whether the speaker was indeed Saddam and whether the broadcast was taped after the U.S. strikes or in advance of them.

There was nothing in the tape that specifically referred to the strike, or other events, that would confirm that it was made after the strike. Even Saddam's reading of the date could have been pre-recorded, officials said.

U.S. government analysts said this was the first time they know of that Saddam wore glasses for a televised address, and they have not made a determination as to whether the speaker was, in fact, the Iraqi leader.

But officials said other foreign intelligence services conducted voice print and other analyses and concluded that, in fact, it was Saddam.

Fox News' Rita Cosby, Rick Leventhal, Major Garrett, Carl Cameron, Bret Baier, Greg Kelly and The Associated Press contributed to this report.