The members of Apache Troop couldn’t see a thing. It was August 2010, 0200 hours. About 120 U.S. and Iraqi soldiers were silently spreading out over a remote farm in northwestern Iraq. Their objective: a mud hut where, according to intelligence reports, two suicide bombers were planning an attack on a checkpoint to coincide with the end of Ramadan. But the allied soldiers, even wearing night vision goggles, couldn’t locate the hut; eight-foot-tall sunflowers obscured their view.

As the troops searched for their target, two U.S. cavalrymen set up on the edge of the squadron, reached into their packs, and withdrew the components of a 4-lb. miniature airplane called the Raven-B. They assembled it in seconds, revved its motor until it buzzed like an angry bee, and threw it into the air. With a hand-held control unit, the soldiers put the aircraft into automatic orbit a few hundred feet above the field. Watching the video transmission from the Raven-B’s infrared camera, they spotted the hut and directed the plane to light up the roof with an infrared laser, which guided the team through the sunflowers to their target. Without firing a shot, they arrested the saboteurs, who were sleeping inside. The suicide vests were buried nearby in a vegetable garden.

When civilians think of the new class of mechanical warriors aiding troops in places like Iraq and Afghanistan, the high-priced, high-tech airplanes that come to mind have names like Predator and Global Hawk, made by General Atomics and Northrop Grumman (NOC), respectively. These unmanned aerial vehicles, or UAVs, operate over the Middle East, conducting in-depth surveillance of potential targets. Some of them are armed. In September, senior al-Qaeda leader Anwar al-Awlaki was killed in Yemen by two CIA-controlled Predators launching Hellfire missiles. On Dec. 4, Iran claimed it recovered a RQ-170 Sentinel, the top-secret stealth drone that was used in the May raid on Osama bin Laden’s compound.

But aircr...