U.S. Troops Pour into Southern Afghanistan in New Offensive

JAMES MATES: They promised decisive action to finally break the Taliban in southern Afghanistan, and this is what it looks like: the biggest airborne operation since Vietnam. Thousands of U.S. Marines, by air and more by land, huge armored convoys heading straight for the Taliban strongholds in the Helmand River valley.

LT. COL. CHRISTIAN CABANISS, U.S. Marine Corps: We've been able to squeeze the whole river valley at the same time. It's really disrupting their ability to reinforce any area, because every area is under pressure at the same time.

JAMES MATES: The British have fought here these last four years. They have won important victories, but have never had the numbers to do more than just maintain a presence. The arrival of this huge U.S. force should change all that.

It has been named Operation Strike of the Sword and is the biggest American assault since the attack on Fallujah in Iraq in 2004. It began at 1 a.m., helicopters inserting troops into the villages of Nawa and Garmsir in the lower Helmand Valley.

By dawn, 4,000 Marines and 650 Afghan troops were in the field.

CAPT. DREW SCHOENMAKER, U.S. Marine Corps: The aim of the air assault was to put Marine Corps back, expeditionary-wise, out and behind enemy lines. We dropped into a few places that nobody had been.

Backlash from the Taliban

We had watched the buildup last week as the Marines readied for today's assault, the sheer numbers of armored vehicles pointing to the U.S. strategy of overwhelming force. The Taliban have little defense against this sort of firepower.

But it will be dangerous. The Taliban will fight. And where they choose not to, they won't go away, but simply fade back into the civilian population.

JIM LEHRER: One U.S. Marine was killed in the first full day of the operation in Helmand province, and several others were wounded.

Separately, the U.S. military announced an American soldier was missing in the east. He was apparently a captive of the Taliban.