After granting its official approval to the first Grands Fonds 300 in 1960, the French Navy explained to the designers that the crown at 3 o'clock posed a problem as it was too vulnerable during underwater manipulations. It asked ZRC to “find a solution” to protect the crown without impeding wrist movement, and above all, to ensure it could not open underwater. The team set to work and developed the famous crown at 6 o'clock, connected to the case using an exclusive system consisting of a canon cut from a single block, making the Grands Fonds 300 the first and only watch to be equipped with a 100% monobloc case. Furthermore, the case is machined in a particular type of steel reinforced with molybdenum that is completely antimagnetic (an absolute necessity for Mine Clearance Divers' Group).
Unidirectional 60 divisions rotating bezel.
Crown protection system with inverted screwed thread with dual sealing.
Case size 40.5mm nonmagnetic 316L steel solid case back.
Automatic winding ETA 2824-2 or SELLITA SW200.
38 hours power reserve.
Sapphire 4 mm.
Natural brown calf tang buckle.