Small, inexpensive and lethal, drones enable everyone from terrorists to the Chinese People’s Liberation Army to engage in what the Pentagon acknowledges is a new arms race with “alarming” consequences. More than 50 countries operate surveillance drones and, increasingly, are fitting them with weapons. …

But American drones are not alone in the sky. Spy drones routinely shadow U.S. aircraft carrier strike groups and other military exercises. Drones crisscross the Persian Gulf. Israeli drones have circled over Gaza during the recent fighting there. Experts say it’s a rare conflict that doesn’t attract spy drones; even the United Nations has considered using drones to monitor the fighting in Congo. …

A new Pentagon study frets that enemy drones could be a “very serious threat” to U.S. aircraft carriers in the Pacific and elsewhere, as well as to “supply convoys and other combat support assets which have not had to deal with an airborne threat in generations.” On the battlefield, an enemy could create chaos and confusion simply by flooding the airspace with drones, and any U.S. bases within drone range would have to be closed, the report said.