Fleets of dozens of mysterious UFO drones are surveilling America’s most sensitive military sites, and the Pentagon admits it can’t do much to stop the aerial intruders, according to a new report.

Drones of unknown origin have been spotted flying over military bases in Virginia and Nevada over the past year, including the secret base for the Navy’s elite SEAL Team Six commando unit and Naval Station Norfolk, the world’s largest naval port, the Wall Street Journal reports.

Federal laws, however, prohibit the military from shooting down the drones over the potential risks to troops and civilians.