When Rolex and Blancpain launched their first wristwatches for divers in the early 1950s they did, in fact, create the archetype of the modern dive watch, thanks to the development of the quintessential rotating bezel. However, they did not invent the first watch used by divers.
If we travel back in time, we find that World War II (and, especially, the frogmen of the Italian Navy) demonstrated the potential of underwater warfare and thus the need for salvage. This, in turn, further increased the need for water-resistant watches in order to better conduct underwater missions involving timing and navigation. The 1940s marked the introduction of various water-resistant watches and, of course, the canteen-style watches that were equipped with little more than an additional crown cap for increased water resistance. Earlier, in the 1930s, there was Panerai supplying the Italian naval divers with various instruments as well as (in cooperation with Rolex) some of the first specifically developed watches for divers. Four years before that, and in a much more civilian environment, Omega launched the rectangular Marine, with a patented double sliding and removable case, which was (at least theoretically) water-resistant to a depth of more than 100 meters. Because of these attributes, the Marine was successfully used by underwater pioneers such as William Beebe (up to 14 meters) and Yves Le Prieur.
But we still have to travel a bit further back to get to the beginning: In the 1920s, wa...