The Pentagon has not been able to find out where the drones came from.
Last December, a flock of several drones flew over the military bases in Virginia in the United States, says The Wall Street Journal.
There were twenty drones. They flew after sunset for 17 days at an altitude of more than a kilometer at a speed of 160 kilometers per hour.
The drones were flying in a no-fly zone over Langley Air Force Base and Norfolk Naval Base.
The US Department of Defense has not been able to find out whether it was drone enthusiasts or foreign intelligence organizations.
US law prohibits shooting down Drones if they do not pose a danger.
Earlier in the fall, five drones were found flying near a nuclear weapons test facility in Nevada, it also says Fox News news channel.