In the beginning, dive watches were pure tools: essential swimming buddies that helped keep divers on time and hence, well, alive. Today they?re something else: fashion statements, conversation pieces, rugged companions for a trip to the beach or pool. This is an excerpt from Timeline: “Dive Watches Through the Decades,” which traces the history of the dive watch from its start in the 1920s, with the invention of the first truly water-resistant cases, to 2014. (Only mechanical watches are included.)
1. Rolex Oyster (1926)

Rolex Oyster, Ref. 679, (1926)
In 1926, watches constructed especially for use by divers appear. They have insulated crowns (the crown is the chief point of entry for water into a watch case). It was also the year that Rolex founder Hans Wilsdorf introduces the Oyster case, which has a screwed crown, screwed caseback, and securely sealing crystal. It is the world?s first truly water-resistant case. One year later, Wilsdorf asks Mercedes Gleitze, a stenographer vying to become the first British woman to swim the English Channel, to wear an Oyster on one of her attempts. She doesn?t make it all the way, but the Rolex she wears around her neck keeps on ticking. 2. Panerai prototypes (1936)

Panerai watch, PAMPR004 (1936)°
The Italian Navy commissions Panerai to develop the first prototypes of a watch that will evolve into the model now known as the ?Radiomir.? The watches, water resistant to 30 meters, go into production two years later. The e...