A revolution is transforming the armed forces of every nation. In "Drones," NOVA launches an investigation of the explosive growth of airborne UAVs or pilotless drones. During the invasion of Iraq in 2003, the U.S. deployed only a handful; now, it has more than 7,000. Besides the U.S., over 40 other nations are now building or buying these increasingly lethal and cost-effective weapons, and it's only a matter of time before a terrorist group turns the technology against Western targets. The latest Predators can track 12 targets at once, trace footprints back to their source and even recognize individual faces. Yesterday's soldiers and pilots put their lives on the line but today, a UAV pilot can "fly" a mission in Afghanistan remotely from a base in Nevada. As one pilot said, after carrying out a strike, "within 20 minutes you can be sitting at the dinner table talking to your kids." That new ability has already saved hundreds if not thousands of U.S. service lives but may make military strikes a more tempting, seemingly risk-free option.