Covert underwater sabotage missions had proved extremely effective during WWII, and a division of highly trained commando divers was considered a postwar necessity.

As well as hand picking members of the new squadron, Maloubier and Riffaud were also expected to select their gear. But with diving very much still in its infancy, the available kit was limited and much of it had to be invented by the men themselves.

That, of course, included a timing device. With nothing suitable in existence that could cope with the demands of the military, the pair sat down with a piece of paper, a pen and a ruler and within two hours had laid down the requirements for a replica rolex day date watches that would serve.

Among them was a high contrast black dial with white hands and indexes, an automatic movement so the crown would have to be used only rarely, a rotating bezel to track immersion times and, naturally, a robust waterproof case.

The list was an extensive one, and daunting to watchmakers of the era. Maloubier was turned down by scores of manufacturers when he put the design out to tender, and only hit on a success when he approached Jean-Jacques Fiechter, the CEO of a small, Swiss company called Blancpain.

Himself an avid diver, it was Fiechter who came up with the idea of making the bezel unidirectional, so it would only overestimate remaining air supplies if it was knocked, which became an important safety feature. He also gave the watch a screw down back for superior water resistance and developed a double O-ring system for the winding crown (with the patent for the screw-in crown held by Rolex with the Oyster case).

The resulting model was christened the Fifty Fathoms, after a British unit of length equal to six feet used to measure water depth. Fifty fathoms, or 300 feet, was considered the maximum a diver could reach at the time.

Thorough testing by the Nageuers de Combat followed, with the swiss replica watches declared a success and going on to become government issue, not only to the French Navy, but to the German, Israeli and Spanish too.

Today, the Fifty Fathoms is available in a wide variety of styles, from faithful recreations of that original catalyst to some contemporary examples of haute horlogerie, complete with flyback chronographs, moonphases and annual calendars.