Recreational drones are selling like hot cakes this holiday season. About 700,000 drones were sold this year, and when the government opened its registry period for unmanned aircraft in mid December, 45,000 drones were signed up in the first two days.

But the problem with having so many drones buzzing around American airspace is that they get in the way of military aircraft attempting to conduct training or rescue operations.

From the Washington Post:

Last month, an Air Force A-29 Super Tucano aircraft reported a near mid-air collision with a small 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-sized drone that passed within 10 feet of its right wing, officials said.

In 2015, there have been 35 cases of small drones colliding or interfering with military aircraft. First responders have been hampered by drones no less than 1,000 times this year. While the drones aren’t exactly shooting aircraft out of the sky, they do force military planes and rescue helicopters to prematurely land before completing their missions. If a helicopter is rushing to a burning building to rescue civilians or a military jet is flying to rendezvous at another location, these landings can spell disaster.

Before this year, the military never encountered rogue drones in the sky. Steven Pennington, the director of all Air Force bases, is now prepping pilots to be wary of errant drones.

“Boys and girls, there’s a change in the world,” he said. “There are small things flying. We know some of them are flying in our terminal areas and they shouldn’t be. We’re working on that. We know that there are some of them flying in around our military training routes and special use airspace. We’re working on that. But the first thing is to tell people to be aware.”