The U.S. military has been using killer drones to take out enemies for years. But those strikes have ordinarily targeted small groups, or lone individuals. Last night, an American pilotless plane reportedly killed 20 people during an attack on a militant compound in Pakistan. It could well be the deadliest drone strike ever.

Pakistan-based guerrillas have emerged as the top threat to American operations in Afghanistan. U.S. Predator and Reaper unmanned aerial vehicles, or UAVs, have become American commanders' weapons of choice to strike back against those militants. The drones can circle above an guerrilla encampment for hours without risking a pilot. But they appear to be less of a political hazard, as well. Ground missions and manned flights by American commandos have enraged the Pakistani leadership, and sparked skirmishes with local soldiers. The drone strikes seem to provoke a more measured reaction – at least, for now. And they provide a bit of plausible deniability to the attacks. Recently a Predator drone went down over Pakistan; the U.S. military swore they had nothing to do with the UAV.

This is at least the 19th UAV attack in Pakistan's tribal areas "since the beginning of August," the *New York Times *notes. "In the first seven months of 2008, there were five strikes." Some of the "strikes are taking place as deep as 25 miles into Pakistani territory." And they are growing increasingly deadly. During one week in September, U.S. drones killed more than 50 people in four attacks.

The Times and other news outlets credit "Predator" drones with strikes. But it's more likely that bigger, brawnier Reaper UAVs are being used, instead. With a payload of 3,750 pounds – compared to the Predator's 450 pounds – the Reaper can carry an assortment of satellite-guided, quarter-ton bombs, as well as Hellfire missiles. They can carry out extraordinarily lethal attacks.

UPDATE: A well-informed source says there have been deadlier drone attacks. "20 isn't close," the source says. "It's just the most for a *reported *strike." Hmmm....

[Photo: USAF]

ALSO: