Actually Rolex manufactured the whole watch for Panerai...both the case and the movement were from Rolex.
At its beginnings Panerai was a supplier for the Italian navy...mostly diving gauges for divers and other stuff...then the navy commissioned them to source a rugged watch for their elite divers unit and they in turn went to Rolex for that.
The case was originally an oyster pocket watch which they attached lugs for the straps...thats why the original first pams have Rolex brevettato crowns...and Rolex sold some left over cases with the Rolex brand, becoming the 6154.
Also...i believe the sterile California dial came from Rolex too.
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