Five drones were detected Thursday night over the submarine base of Île Longue, in Brittany, western France, a strategic military site home to ballistic missile submarines, the AFP reported, citing the the French gendarmerie, which is part of the military. The submarines harbored at the base carry nuclear weapons and are a key part of France’s nuclear deterrent.

French navy troops in charge of protecting the base opened fire, the report said. It was unclear whether the drones were shot down.