I think it depends on your definition. Omega had a water resistant watch in the 30's called the marine or something like that but it was for swimming and had no timing bezel.
Rolex had a watch with a timing bezel first but it wasn't a diver. I think Blancpain beat Rolex by maybe a year to making the first dive watch by putting a timing bezel onto a water resistant watch and marketing it for diving as the 50 fathoms.
I would say that most people credit either Rolex or Blancpain for the first true dive watch.
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