The Air Force revolutionized drone warfare. Now it's finding itself on the defensive.

Rogue toy drones - a hot-selling Christmas gift this season and last - are starting to interfere with military operations at several bases across the country. With sales of consumer drones expected to approach 700,000 this year, military officials say they are bracing for the problem to get worse and are worried about the potential for an aviation disaster.

Last month, an Air Force A-29 Super Tucano aircraft reported a near-collision with a rogue drone over the Grand Bay Bombing and Gunnery Range in Georgia, Air Force officials said.

In June, an Air Force KC-10 aerial refueling tanker flying over the Philadelphia suburbs at an altitude of 3,800 feet was forced to take evasive action and barely avoided striking a football-size drone, officials said.

There have been at least 35 cases of small drones interfering with military aircraft or operating too close to military airfields in 2015, according to reports filed with the armed forces or the FAA. That's a small fraction of the estimated 1,000 reports received by the FAA this year of small drones interfering with civilian air traffic or coming too close to passenger airports.

But military officials, who once thought the remote locations of their airfields and restricted airspace offered a measure of protection from wandering drones, said they are no longer immune.

Cmdr. William Marks, a Navy spokesman at the Pentagon, said Navy pilots or air-traffic controllers at U.S. bases have reported close calls or encounters with unauthorized drones 12 times in the last three months. Prior to that, the Navy was recording an average of less than one incident per month. "We're seeing an exponential curve, so yes, it is a concern," he said.

One military airfield that has experienced multiple risky encounters with drones is the Marine Corps Air Station in Yuma, Ariz.

In May, a Marine Corps Harrier jet coming in for a landing at Yuma reported a small blue drone about 100 feet off its right side. In July, a Navy T-45 Goshawk training aircraft flew within 100 feet of another drone about five miles west of Yuma, according to FAA records.

Col. Robert Huber, a senior Army aviation official, said his service has not received any reports of problems with rogue drones on Army installations so far. But given the experiences of other branches of the military, he said the Army anticipates "that there could be more challenges."

Prior to last year, close encounters with rogue drones were almost unheard of. But rapid advances in technology and falling prices have led to a boom in sales - and a corresponding surge in reports of air-traffic chaos.