While it is not unusual for rocket-propelled grenades — normally an anti-tank weapon — to hit helicopters, it is extremely rare for them to actually bring one down.

Coalition officials have effectively ruled out that the helicopter was brought down by anything more sophisticated than an RPG launcher. That dispels fears the Taliban had suddenly acquired more sophisticated weapons such as the Stinger missiles used to such devastating effect by mujahideen fighters against Soviet aircraft during the occupation of the 1980s.

RPGs have an effective range of about 300 meters, although officials in Kabul say the shot that downed the Chinook would have to have been fired well within 100 metres of its target.

“You have to understand the terrain surrounding the valley. The shot could have come from a low angle, or even from above the helicopter,” one military official said.

What is not known for sure now is whether the helicopter caught fire or exploded, or whether it fell from any considerable height. Officials acknowledge that the destruction was devastating, something supported by the fact it took about four days to gather all of the wreckage and remains.