As they waited in a convoy Monday to cross the Euphrates River, the Marines were tense, fingers on the trigger.
Two bloody battles a day earlier near An Nasiriyah, 230 miles from Baghdad, had deepened their sense of just how treacherous the drive to the Iraqi capital could be. Some of the Americans had been killed by Iraqis pretending to surrender.
The convoy of hundreds of vehicles -- including tanks, TOW missiles and armored personnel carriers -- was backed up along the road leading to a pontoon bridge, and Marines with scarves around their heads lay in the sand on either side of the line of traffic, pointing their M-16s toward the desert. Anyone who approached faced close scrutiny.
The point man for one set of vehicles, a young Marine with a quiet Southern drawl, seemed typical of the mood. As he spoke, his gaze was fixed straight ahead, his finger on the trigger of his rifle, ready for whatever might lie across the sand.
His eyes looked tired. He had had about an hour of sleep a night over the previous few days as the convoy pressed ahead.
"It's going to be a long day, I think," he said. Asked if he had drawn any fire, he said "Not yet. When we reach Baghdad, I think."
Like other Marines interviewed Monday, he refused to give his name. Such was the mood.
Another Marine, from the Twentynine Palms Marine Corps base in California, was in the 1991 Gulf War, and noted the change in mood this time.
"When you're at war in someone's homeland, it's a different story," he said. "Last time" -- in Kuwait -- "everyone was happy to see us. We were liberating the country. So we did it, we won, everyone was happy and we went home."
But here, there is constant anxiety about disguised Iraqi soldiers waiting to attack, and constant wondering about just who is the enemy.
"We saw some black berets hanging up in a tree, and we went to investigate and we saw all these uniforms hanging there. I figure half these guys you see walking around are soldiers. They've discarded their uniforms," the Marine said. "They're out there, they're watching us and they're planning small counter-attacks."
Meanwhile, outside the Shiite holy city of Najaf, at the northern end of the advance, U.S. soldiers skirmished with Iraqi forces before dawn Monday.
Officials would not say when they expected to arrive at the capital city. "We'll arrive in the vicinity of Baghdad soon, and I prefer to leave it at that," said Lt. Gen. John Abizaid of U.S. Central Command.
Because of the resistance at An Nasiriyah, Marine officials said they expected to sidestep the city rather than fight to capture it -- the same strategy they employed in Basra.
American authorities detailed two bloody battles there on Sunday:
-- Marines encountered Iraqi troops who appeared to be surrendering. Instead, they attacked. The Americans triumphed, knocking out eight tanks, some anti-aircraft batteries, some artillery and infantry, Abizaid said. But victory came at a cost: as many as nine dead and an undisclosed number of wounded.
-- A six-vehicle Army supply convoy apparently took a wrong turn and was ambushed. The vehicles were destroyed, and a dozen soldiers were missing. Iraqi television showed five captured Americans and four bodies it said were of U.S. soldiers.
The Iraqis were jubilant. "Our valiant forces were lying in wait for them, inflicting heavy losses on the covetous invaders, killing at least 25 of them, and injuring a large number of them. Also, a number of their mercenaries were captured," the Iraqi military said in a communique.
Separately, two British soldiers were missing after coming under attack Sunday in southern Iraq, the British Defense Ministry said.
Near Najaf, units from the U.S. 2nd Brigade skirmished with Iraqi paramilitary forces, who fired rockets, small mortars and antiaircraft guns. U.S. forces drove them back with heavy tank and artillery fire, using a counterbattery that zeroes in quickly on the source of incoming fire.
Generally, the Iraqis were kept too far back to harm to U.S. troops, whose weapons had greater range, and no American casualties were reported.