The drone revolution has been downsized. Unlike manned aircraft, the wide variety of unmanned aircraft systems employed by the U.S. military — known colloquially as drones — can fly directly over hostile territory without placing pilots or ground troops at risk of injury, capture, or death.

These systems have proven extraordinarily effective in the war on terror, collecting surveillance and even killing more than 50 al Qaeda leaders by virtue of the powerful missiles they can employ.

But the heavy firepower that makes large drones like the Predator so fearsome can have drawbacks. The 110-pound Hellfire missiles commonly carried by the Predator can pierce tank armor and pack a lethal punch, but are difficult to employ in crowded urban environments.

When facing an enemy who can blend in with the local population, U.S. troops need small but lethal weapons that can strike with surgical precision and limit collateral damage.

Toward that end, micro-drones — think flying cameras — are already being used for surveillance in hotspots across the world. Operated like hobbyists' model aircraft, with hand controls, these drones can be sent out by troops on patrol. Their quiet electric motors allow them to monitor without tipping off the enemy.

Until recently, these pint-sized robots have been too lightweight to arm. But thanks to the same technology that powers our smartphones, defense companies are flight-testing ever-smaller drones packed with miniature explosives that can be delivered with pinpoint accuracy.

For example, Raytheon's Pyros is a scaled-down, miniature munition with all the features of full-scale precision bomb. And it weighs just 12 pounds — about a tenth the weight of a Hellfire.

Likewise, General Dynamics has designed a "smart" air-dropped mortar that lands within seven meters of its designated target. And the Switchblade, developed by AeroVironment, is small enough to fit in a soldier's rucksack and can be flown directly into a target with a hand grenade-sized warhead, thus minimizing collateral damage.

Downsized drones and their weapons offer a solution to one of the key challenges of modern warfare. Our enemies know they cannot take on the U.S. military conventionally, so they purposefully bunker in difficult places, such as schools, religious sites, or civilian neighborhoods.

Larger drones are powerless to attack in these areas. Strikes that are aimed at terrorists but kill noncombatants can stoke local backlash and turn communities against U.S. troops. Smaller, more accurate bombs make it possible to reach high-value targets without putting innocent bystanders or protected sites at undue risk.

Drones don't just protect noncombatants, of course. They also ensure that more of our troops and allies will return home safely. Marines in Afghanistan and Iraq have found small drones to be the best defense against roadside bombs. Ground units now regularly send small drones ahead of convoys to patrol roadways.

With defense budgets tightening, drones are an essential tool for a leaner, more cost-effective fighting force. They offer greater versatility, yet are cheaper to maintain and operate than manned aircraft.

The world remains a dangerous place because those who would kill us don't follow the rules of combat. The new generation of smaller drones represents the best of American military technology and capability, combining both lethality and precision. Our troops and the people they defend deserve nothing less.

J. Michael Barrett is former director of strategy for the White House Homeland Security Council. He is a frequent national security commentator and a principal with the D.C.-based consulting firm Diligent Innovations.