Five years ago, the Pentagon was on cusp of an air-combat revolution. For a few brief, heady months in late 2005, it looked like the U.S. military might soon launch full-scale development of a new class of fast, lethal Unmanned Aerial Vehicles eventually capable of replacing all kinds of fighter jets, from the older F-15s, F-16s, and F-18s to the latest F-22s. But the revolution fizzled when the Air Force abandoned its share of the so-called Joint Unmanned Combat Air System effort. Manned jets continued to dominate, culminating in today’s mammoth, $300-billion F-35 program.

The embers of upheaval kept burning, almost invisibly. The technology from the 2005 effort survived in various forms, slowly maturing amid a growing demand for combat UAVs. Today, no fewer than three separate killer drone designs — two of them direct descendants of the original J-UCAS demonstrators — have converged on two airfields in California for flight tests. The revolution flared up again without many people noticing. While the F-35 still gobbles up the bulk of the Pentagon’s fighter funding, jet-powered killer drones are back — and revolution is once again a real prospect.

High-endurance armed drones such as the General Atomics Predator have been a fixture of U.S. military operations since the mid-’90s air war over the Balkans. Besides being cheaper to buy and operate, robot aircraft carry fuel in place of a pilot and so can stay in the air longer. Plus, if they crash or get shot down, nobody gets hurt. That means the military can assign drones to what one robot industry insider called the “worst down-and-dirty missions that even the nuttiest pilot wouldn’t want to do.”

But today’s drones are “fair-weather” killers, too slow to survive the sophisticated air defenses of, say, China or Iran. To bring the advantages of robot aircraft to high-intensity warfare, the Defense Advanced Research Projects Agency along with the Air Force and Navy sponsored J-UCAS starting in 2003. Boeing’s X-45 (pictured) competed with the Northrop Grumman-built X-47 to “demonstrate the technical feasibility, military utility and operational value for a networked system of high performance, weaponized unmanned air vehicles,” according to Darpa.