Because of the NATO force's heavy reliance on them, one of the most eye-catching revelations in a trove of classified documents posted on the Internet this week was that insurgents apparently used a portable heat-seeking surface-to-air missile to shoot down a twin-rotor CH-47 Chinook in Helmand province in May 2007, killing seven Western service members.

According to the classified document, if the Taliban and other insurgent groups possessed large numbers of these weapons, it could dramatically alter the dynamics of a war effort that already is struggling.

Shoulder-launched missiles downed scores of Soviet helicopters in the 1980s, helping ragtag Afghan rebels prevail against a vastly superior force.

Most experts believe that the anti-aircraft threat currently posed by the insurgents is relatively limited, and that they don't have significant stocks of surface-to-air missiles, at least for now.

The shooting down of choppers remains a relative rarity in the Afghan conflict, and heavy machine guns and rocket-propelled grenades are almost always found to have been used.

"After nine years, if they had a lot of them, we would have seen them by now," said a U.S. official who spoke on condition of anonymity.

By their nature, shoulder-launched missiles - "manpads," in military parlance - are easily transportable, making them less difficult to smuggle than bulkier weapons systems. Mujahid declined to discuss any recent additions to the Taliban arsenal, but said, "It is difficult to stop weapons trafficking. The world's black market is open to us." (ANI)