The next Rolex pictured below is called a Hermetic watch and it was made in 1924. This new style of watch completely protected the entire movement, and notice that when it is sealed the watch winding crown is hidden inside the watch.
Think of a Hermetically sealed watch as being like a jar lid (with a round glass window) screwed on a jar. Once the lid is screwed into place, it forms an impervious barrier. No liquid can get in or out of the jar when the lid is securely screwed into place. (This of course is if you do not submerge the watch in deep water. At some point, without a gasket the case would fail and let water in).
This design was revolutionary at the time because it consited of two pieces. Basically you would spin the threaded cap off the front of the watch (think jar lid). The challenge was, in order to change the time or wind the watch–every day–you had to spin-off the top, every time, and then, spin it back on afterward. Even though it worked, this design was short lived because it was a bit like having the on-off switch for the windshield wipers in the glove compartment of your car.
Notice also the face of the cap has a machined or fluted edge to make it easy to grip. Another challenge, was, that over time, the fluted bezel would wear down so if you used it for a long time, eventually you would no longer be able to grip the face to twist it off.
This machined edge or fluted bezel is the genesis for the fluted bezels on modern Rolex watches, including the Day-Date, Datejust and even on the sport Rolex professional models like the Submariner and GMT Master.