Traditionally, special forces operate covertly.

But, highly unusually, within hours of their deployment, the Pentagon was playing video clips of them in action.

The soldiers were shown packing their gear, boarding aircraft, and then parachuting - dozens of them - out of the backs of C130 aircraft.

They landed by an airfield in southern Afghanistan.

Their mission, we were told, was to clear the airfield building by building.

In the grainy, green vision of a night-scope, we saw the soldiers come across a weapons cache.

The Chairman of the Joint Chiefs of Staff, General Richard Myers, said that the American forces had encountered some opposition.

"You could call it light", he said, adding that it was easy in the comfort of the Pentagon briefing room to suggest that any armed resistance is easily dealt with.

Taleban 'lie'

Two soldiers had been injured in the parachute drops, along with the two who had been killed when their helicopter apparently crashed inside Pakistan.

General Myers said that it was a Taleban "lie" that the helicopter had been shot down; he said the most likely early explanation was linked to the dust thrown up by the rotors.

He said there had been two targets inside Afhganistan... the airfield and also a Taleban command and control centre - which was one of the locations lived in by the Taleban leader, Mullah Mohammad Omar.

General Myers said that these targets could have been taken out with bombs, but that would have denied the opportunity to gather intelligence, one of the primary objectives in this mission.

Pentagon message

This deployment marks a new phase in the American military campaign.

It had been foreshadowed by the comment from Defence Secretary Donald Rumsfled earlier in the week, when he had conceded that strike aircraft "can't crawl around on the ground and find people".

And US aircraft had broadcast messages to Afghan people instructing them not to impede any American forces they came across on the ground.

It had been known that special forces had already been operating in the north and the west of Afghanistan - but that is thought to have been limited to pinpointing targets for the airstrikes and to liaising with anti-Taleban forces.

This deployment was in the south of the country, near the Taleban stronghold of Kandahar.

It does not mean that we are on the brink of a full American infantry invasion.

But the message the Pentagon would like to send is that it can put its soldiers' boots on the ground at a time and a place of its choosing.