They have been used to attack militants in Pakistan and Afghanistan. But are their benefits outweighed by backlash on the ground?
What is a drone?
Drones, or unmanned aerial vehicles (UAVs), are remote-controlled aircraft that usually carry cameras to gather intelligence and sometimes missiles to kill.
They range in size from the five-pound Raven, which is launched by an infantryman the way a child throws a paper airplane and costs $25,000 (though a full "system" consisting of three of the planes, a ground control station, and imaging equipment goes for $250,000), to the Reaper, which has a wingspan of 66 feet and is equipped with Hellfire missiles and 500-pound bombs and has a price tag of $17 million.
Though the Navy flew unmanned planes during World War II, the technology didn't catch on until the 2002 invasion of Afghanistan. Then, the US only had a handful of them. Today, there are 7,000 of them in the US arsenal.
What are they good for?
They're particularly useful in theaters like Afghanistan and the tribal areas of Pakistan, where rough terrain and hostile locals make on-the-ground intelligence gathering even tougher than normal. The key to their success is the cameras they carry – and the images they transmit instantly to infantry commanders.
Most drones spend their days looking for improvised explosive devices along roads, flying over villages that troops may be planning to pass through, or watching houses thought to be used by militants.
Most famous are the Predators and Reapers – the missile-wielding planes that have been used to attack militants in Afghanistan and Pakistan and whose pilots are often a world away, on bases in Arizona and Nevada.
Drones' great advantage is that they keep pilots and soldiers out of harm's way. They are also much cheaper to fly than conventional planes.
"Unmanned systems are used for jobs that meet one of the three D's: dull, dirty, or dangerous," says Peter Singer, a senior fellow at the Brookings Institution in Washington and author of "Wired for War," which considers the ethical and strategic implications of the burgeoning use of UAVs and other military robots.
"The most important 'D' in my mind is 'dangerous,' " he continues. "As a commander of one of these units told me, he likes them because he doesn't have to worry about writing a letter to someone's mother."
Are they helping the US military?
The lethal UAVs work as advertised. "By one count, 11 out of the top 20 [Al Qaeda] leaders we have killed have been killed by robotics, not by boots on the ground," Mr. Singer says.
The drones are credited with killing high-value targets in Pakistan's tribal areas, an effective no-go area for the US military. In January, for example, a drone killed Osama al-Kini, thought to be the architect of a 2007 attack on the Marriott Hotel in Islamabad that killed 54 people.
In a sign of growing US support for drones, all branches of the military – as well as the CIA – are adopting the technology. The military spent $880 million buying such planes in 2007 and is now spending $2 billion a year on them.
In a speech at the Air War College in Alabama last month, Defense Secretary Robert Gates said there had been a 48 percent increase in UAV patrols in combat zones in the past year, to 34 a day. Since last August, the US has carried out about 40 unmanned airstrikes in Pakistan.
Are there strategic costs?
Some analysts worry that, despite the drones' tactical benefits, their heavy use could damage America's strategic goals. David Kilcullen, one of the most influential advisers in US counterinsurgency strategy in the past few years, thinks drone strikes in Pakistan do more harm than good because of the backlash they create, especially when civilians are killed.
"Unilateral strikes against targets inside Pakistan, whatever other purpose they might serve, have an unarguably and entirely negative effect on Pakistani stability," he wrote in the Small Wars Journal earlier this year.
"They increase the number and radicalism of Pakistanis who support extremism, and thus undermine the key strategic program of building a willing and capable partner in Pakistan," he continued.
Singer also points out that, while the US may hope that technological superiority will inspire fear or at least respect from enemies, to many tribal Afghans and Pakistanis the use of such weapons is seen as dishonorable because the soldiers deploying them aren't taking any risks themselves.
Is Pakistan going to stand for this?
The drone attacks are a clear source of public anger inside Pakistan. Leaders in Islamabad have repeatedly, even angrily, demanded that the US halt drone attacks in their country. But US officials privately say they cooperate closely in choosing targets for strikes with the Pakistani military, and that the US has tacit approval for most of its drone operations inside Pakistan's tribal areas.
Still, the airstrikes undermine the Pakistani government by setting it against the populace, which largely opposes the attacks on fellow Pakistanis.