The two Iranian-designed Abadil-1 drones that Hamas flew from the Gaza Strip into Israel last week were little more than over-glorified toy planes. So why did the Israeli military shoot them down with $3 million Patriot missiles? After all, Israel has multiple Iron Dome missile-defense batteries in the south of the country.

In all likelihood, the Patriot crew were the first to detect and track the invading drones. And not knowing exactly what they were facing, the Israeli Defense Forces took no chances.

While the drones were destroyed, the episode shows the limits of conventional interceptors. If Hamas had sent a dozen drones, Israel would have had to waste missiles on them all. That's why Rafael Advanced Defense Systems, the same government-owned company that built Iron Dome, is developing a laser system called Iron Beam.

Lasers have great potential as weapons. Laser beams travel at the speed of light, so no rocket will ever outrun them. They are also remarkably cheap to generate—a couple dollars a pop, compared to launching a five, six or even seven-figure missile. And as long as you've got electrical power, a laser cannon will never run out of ammunition. Lasers are also versatile. They don't have to blow up a target to neutralize it. They can fry electronics, sensors and navigation systems.

In the past, advocates of laser weapons tended to promise too much too soon. During the Cold War, the Strategic Defense Initiative, or "Star Wars," was supposed to develop a space-based laser defense system to protect the U.S. from intercontinental ballistic missiles. But $30 billion later, America had not a single miniature orbiting Death Star.