In the early 1960s, Louis Brunet and the Annecy diving team, with the support of local figures such as Louis Servetaz and Mr. Bouchet, launched plans for an affordable and efficient diving watch. ZRC sales supervisor Mr. Bourdarian worked alongside Mr. Pastre and Mr. Digne, then watchmakers in Toulon, who specialized in commercial relations with the French Navy. Together, they formed a partnership to develop the Grands Fonds 300 watch. Following its referencing of the first watch, the French Navy explained to the designers that the crown located 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 under water. The team resumed their work and developed the famous crown at 6 o’clock, connected to the case using an exclusive system consisting of a machined canon, making the Grands Fonds the first and only watch to be equipped with a 100% single-piece case. Furthermore, the case is machined from a particular type of steel reinforced with magnesium that is completely non-magnetic: an absolute necessity for the mine clearance divers of the French Navy. ZRC developed an exclusive retractable lug specific to the space between the horns, which only allows the crown to pass through or the strap to rotate in the closed position, making submerging the watch impossible if the crown is not ZRC fully screwed down.