In one of his more elaborate metaphors Nato's redoutable spokesman Jamie Shea tried to play down the potential significance of the use - or as it now seems - the non-use of the US Apache helicopters currently based in Albania.

The Apaches, he said, were not like the Seventh Cavalry who would ride over the hill as the last reel of the movie began to rescue Nato's air campaign.

They were but one more weapons system, that would be brought into play at a time of the Nato commander's choosing.

The BBC's Jon Leyne: "Doubts have resurfaced about the campaign"

That time has not yet come. Two Apache's have already been lost in training accidents. And two air-crew have lost their lives.

The Apaches are still hovering in Albania, with political and military caution in Washington condemning them to a role on the side-lines.

Like so much of the Nato air campaign, the Apaches are in a sense victims of their own press machine. These are said to be among the most devastating weapons in the US Army's arsenal. The Apache is a fearsome killer of enemy armoured vehicles armed with anti-tank missiles and a devastating cannon.

Deployed alongside Multiple-Launch Rocket Systems - the MLRS - capable of firing the long-range TACMS missile - the Apaches, it was thought, would zoom into Kosovo after a preliminary bombardment had neutralised any air defences in their path.

No front line

The reality has been rather different. The Apaches have not been used and probably for justifiable reasons.

US says the Apaches are ready for action

Their combat role is to range ahead of their own forces destroying enemy vehicles in their path. This assumes that any threat to them in a highly mobile battle is some 180 degrees to their front, a risk with which they are well-trained to deal.

But given the way Yugoslav units are dispersed in Kosovo and in the absence of any ground incursion by Nato forces, the Apaches will have no front line ahead of which to operate.

They will face danger from lethal hand-held surface to air missiles from a full 360 degree circle around them.

No wonder then that the Pentagon and the White House have weighed up the risks to this all-American force and decided that for now the Apache's should simply wait this one out.

Some limited missions may be flown to attack Yugoslav forces near to the Albanian frontier.