As US military forces pursue terrorists beyond Afghanistan, the campaign to track down Al Qaeda and Taliban holdouts offers initial lessons on the challenges for America's military in waging unconventional war against shadowy targets.
Afghanistan, on one hand, has showcased innovations in the use of US surveillance technology, precise weaponry, and highly trained special-operations troops - all vital for the dangerous game of hide-and-seek with suspected Al Qaeda terrorists.
Yet the complicated phase of rounding up Al Qaeda leaders and eliminating pockets of resistance has also illustrated gaps and limitations in the US antiterror arsenal. It underscores how even the most sophisticated targeting technology is of little use without solid human intelligence for identifying what to strike.
"Human intelligence ... is one of the sources we have overlooked in the last 20 years," says one defense official. "When you come to asymmetric threats, that's a whole different animal. It is something you can't track via satellite."
Questions over US weaknesses are important. The cat-and-mouse hunt for scattered Al Qaeda remnants - in contrast to the quick toppling of the Taliban regime - is likely to be better represent the kinds of challenges US forces could face in rooting out terrorists from within other nations, such as the Philippines, Somalia, or Yemen.
One early lesson from the skies over Afghanistan is the degree to which US military technology - including new unmanned surveillance aircraft such as Global Hawk and Predator as well as upgraded cold war-era systems - allowed for a more continuous, crisp, real-time picture of the battlefield. Links between different reconnaissance craft allowed the military to essentially zoom in to identify targets - from a blip on a screen to a specific make of vehicle.
"Our overall picture was certainly clearer, and assets like the Predator and its ability to linger without putting people at risk was significant," says Col. Rick Thomas of US Central Command in Tampa, Fla.
This real-time imagery has significantly shortened the time required between identifying a target, striking it, and assessing the damage inflicted, compared with earlier conflicts such as the 1991 Gulf War. Combined with the use of precision-guided weapons, and spotters on the ground, the imagery "gave us an accuracy that surpasses any air campaign we've conducted so far," says Colonel Thomas.
Meanwhile, better links exist for sharing surveillance information among decisionmakers - from air commanders based at the Prince Sultan Airbase in Saudi Arabia, to F-15 pilots, to Special Operations Forces on the ground in Afghan provinces.
Still, Afghanistan also revealed technological glitches that remain in data sharing and the limitations of existing sensors and weaponry against hidden underground targets. It's apparent, too, that there's much work to be done before the US military is able to fully integrate its sea, land, and ground forces for fighting unconventional enemies such as terrorist groups - as opposed to linear battles.
Another major innovation of the Afghanistan campaign was the use of Special Operations Forces (SOF) - highly skilled teams of elite Green Berets to guide operations for both US air power and Afghan anti-Taliban forces.
The strategy essentially turned on its head the traditional practice of using air power to back up a large ground force, and instead used dispersed groups of minimally armed ground forces as a spearhead to help guide and direct a large range of firepower from the sky.
Afghanistan also highlighted the skill with which special operations commandos, especially Green Berets who are trained in languages, can cooperate with local forces while keeping a relatively low profile - capabilities that are likely to see them deployed in other antiterror actions.
Indeed, some 160 of the elite US troops with more than 500 support personnel are currently headed for the Philippines to advise and train the Philippine military in its fight against Muslim extremist groups with links to Al Qaeda.
Nevertheless, use of a small ground contingent, while reducing both the risk to American lives and political opposition from Afghans, meant US forces lacked adequate manpower of its own to block escape routes and capture fleeing opposition members - a factor that may have helped hundreds of enemy fighters slip away.
The campaign has also demonstrated how the abundance of high-tech US intelligence, from satellite imagery to signals interception, has failed to make up for a shortfall of human intelligence sources. Credible informants are especially needed to help target and root out the pockets of Al Qaeda and Taliban resistance in Afghanistan, a task far more difficult than striking at Taliban troop concentrations.