Hi Roger,
"round about" 1965 (that?s the year i?ve seen it in the catalogues first):
Reference 7006 / model M3246BR18: "Men?s specialty watch, DEEP DIVER gyromatic, factory-tested to underwater pressure of 650 feet as long as case, crystal, crown are intact. Revolving bezel shows elapsed time. Stainless steel"
The later (aout 1969) 2-crown version with inner rotating disc is pictured in this thread.
And GP?s first dive watch?
As so often, i?d say: It depends. GP had a model named "Sea Hawk" in the 1940?s, which was water resistant with a container-type case. This may be regarded GP?s first watch intended to use in/under water; but in the sense of a classic diver?s watch with screw-down crown and back and rotatable bezel, it?s the Deep Diver.
And one of the earliest waterproof watches by Mimo (GP?s sister brand) is this model, from a 1920?s catalogue:
