The incident follows a string of recent drone incursions in NATO airspace.

The French navy opened fire at drones that were detected over a highly-sensitive military site harboring French nuclear submarines, according to newswire Agence France-Presse.

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.