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

"I want to make sure you understand ... we're attempting to seize the population. We're going to seize the population from the Taliban and never let them go," said Lieutenant-Colonel Christian Cabaniss, commander of the 2nd battalion, 8th Marines.

Mir said this was crucial.

"This is what McChrystal, I think, has grasped in Afghanistan -- to reach out to Afghan people and try and bring them on board instead of alienating them," said Mir.

Military commanders hope by the end of the summer to provide security for 90 percent of the population in the south, up from about 60 percent now.

WHAT ABOUT RECONSTRUCTION AND DEVELOPMENT?

Poor security has largely kept foreign aid organisations out of the south, particularly in Helmand.

The Afghan government and foreign military commanders hope by securing and holding parts of Helmand, aid organisations will be able to move in and begin reconstruction in an area that has seen little or no development.

"In this district the people have asked the government to help them. This operation will improve things," said Daoud Ahmadi, spokesman for the governor of Helmand.

Saleem Zmarial, adviser to Helmand's governor on development and counter narcotics, said: "The people there need to start a new life with access to healthcare and clean water".

WILL IT BE A LONG FIGHT?

While military commanders hope their overwhelming numbers will overpower the insurgents with little resistance, Taliban fighters have had years to reinforce positions among the valley's irrigation ditches and canals, fiercely resisting past advances.

The Taliban say they will oppose the Marines but are unlikely to challenge them in face-to-face combat, which they would almost certainly lose. The insurgents are more likely to dig in and use deadly roadside bombs and similar tactics.