Q&A - How will new assault change the war in Afghanistan?

By Jonathon Burch

KABUL (Reuters) - Thousands of U.S. Marines stormed into a river valley in southern Helmand province on Thursday in an operation seeking to break the Taliban's hold on the key opium-growing region and turn the tide of the war in Afghanistan.

Following are questions and answers about what impact Operation Khanjar, or "Strike of the Sword," might have.

WHAT ARE THEY TRYING TO ACHIEVE?

The Marines hope by appearing suddenly and in overwhelming numbers, they can capture some of the Taliban's firmest strongholds with little resistance. U.S. commanders say a rapid, decisive victory in the Helmand valley will turn the course of a war some in Washington have said they are not winning.

But launching such a bold operation also carries great risk. A protracted, bloody fight could erode support for the war in the United States, among its NATO allies and, most importantly, among Afghans the U.S. government and military are trying to win over.

"In every counter-insurgency there are times when you have to go in after the insurgents. There are no retired insurgents, but we can't afford to make more enemies along the way," General Stanley McChrystal, who has taken over foreign forces in Afghanistan with a new counter-insurgency strategy, has said.

WILL THEY BE ABLE TO HOLD THE GROUND THEY WIN?

That has been the biggest problem so far for overstretched, British-led NATO troops in Helmand. Without enough manpower, they have been forced to defend scattered outposts and move into areas by day, only to withdraw back to barracks hours later and watch the Taliban flood back in.