Now, the Marines say their new mission, called Operation Khanjar, will include more troops and resources than ever before, as well as a commitment by the troops to live and patrol near population centres to ensure that residents are protected. More than 600 Afghan soldiers and police officers are also involved.

“What makes Operation Khanjar different from those that have occurred before is the massive size of the force introduced, the speed at which it will insert, and the fact that where we go we will stay, and where we stay, we will hold, build and work toward transition of all security responsibilities to Afghan forces,” Marine commander Brig Gen Larry Nicholson said in a statement.

The Marines will be pushing into areas where NATO and Afghan troops have not previously established a permanent presence.

The goal of the operation is to put pressure on the Taliban “and to show our commitment to the Afghan people that when we come in we are going to stay long enough to set up their own institutions”, he said.

The 21,000 additional American troops that Obama authorised almost precisely matches the original number of additional troops that George W Bush sent to Iraq two years ago. It will bring the overall American deployment in Afghanistan to more than 60,000 troops. But Obama avoided calling it a surge.