From their platoon leader, Lt. Adrian Heath, 24, of Phoenix, they were warned not to act like they had all the answers.

"These guys have been through a lot. Listen to what they have to say. Be very humble around here," he told Higgins and Jimenez when they arrived at his platoon.

As he passed out body armor to them, Vines warned the Marines about the hazards in Iraq. That the enemy will wait to ambush convoys about 100 meters to 200 meters from the road. That they will shoot at them with rifles and maybe with mortars. Snipers are always a hazard. "Pay attention to your surroundings," he said. "Pay attention to what the enemy is doing."

Mundy told them that their unit's exploits can be traced from World War II, Korea, Vietnam - all the way to the most recent days of this war.

"You are part of a proud and illustrious history," he said.

But this war is different from past wars. There are suicide bombers, paramilitary groups and combatants dressed as civilians. He challenged the Marines to do their best to distinguish between friend and foe on the battlefield.

"We don't mean any noncombatant harm, but if anyone takes arms against us, they are going to die, and they are going to die quickly," he said. "It's been a fast couple of weeks. Welcome to 3/5. Welcome to Iraq."

Then it was time for the new Marines to join the fighting. If they were overwhelmed or afraid after all the warnings, they had no time for reflection. They were directed to waiting Humvees and driven to the front lines.

But as Jimenez traveled out to his new platoon, where he would spend his first night in a fighting hole, he appeared most disturbed at the prospect of taking someone's life.

"I love being a Marine. I love being a grunt, but I don't know about killing people," he said, bumping up and down in the back of a Humvee. "But if someone out there would try to keep me from seeing my family again, I will."