So what makes a Rolex Oyster an Oyster? The winding crown acts like a screw-on cap, or micro jar-lid, and has watertight gaskets in it. The best way to think of it is to imagine a submarine hatch that is threaded and has to be twisted or spun open or closed.
Hans came up with the idea of associating the fantasy of mermaids with the waterproof Rolex Oyster as seen in the 1926 French Rolex advertisement seen below.
1926 French Rolex Mermaid Oyster Poster
At the same time, as seen in the Rolex illustration below, Hans Wilsdorf came up with a brilliant idea to have authorized Rolex dealers display the waterproof Rolex Oysters watches, in fish-tanks, in their windows–with real fish swimming around the watch!!! This of course gained the fascination of many passer-bys.
In 1927, Hans Wilsdorf learned about a swimmer named Mercedes Gleitze, who claimed to have been the first woman to swim all the way across the English channel. He also read about how another woman claimed to achieve the same feat soon after, in even less time. The second woman, soon afterward, admitted she lied.
As a result, people pointed the finger at Mercedes Gleitze and accused her of lying as well. Mercedes was enraged by the accusation, and declared, that she would "vindicate" herself, but swimming it a second time.
Upon learning of this upcoming event, Hans Wilsdorf contacted Mercedes Gleitze and offered to hire her as the first Rolex ambassador to endorse the brand, by wearing a Rolex Oyster (strangely, on a necklace) on her vindication swim across the English Channel.
The photo below was taken on the beach in France, as Mercedes dove into the water to begin her "vindication" swim.
The challenge with Mercedes Gleitze's "vindication" swim was that after 10 hours, she only made it about 4/5 of the way across the channel and had to be pulled-out, since she almost froze to death. The vindication swim was not a complete success, but the Rolex Oyster, strapped around her neck, came out of the water in perfect working order.
The photo below is of Mercedes Gleitze's actual Rolex Oyster which she wore around her neck, during her vindication swim.