Pictured below is another Rolex wristwatch from 1915, this time with a snap front Hunting Case and if you look closely you notice it is simply a pocket-watch with lugs soldered onto the case, along with a leather piece sewn onto the wired lugs–very primitive and fragile by todays standards.
The reason it had the snap front case-cover was to help protect the glass crystal from getting cracked when a gentleman went hunting.
It is important to note, prior to World War I, wrist watches for men did not exist. Ladies wore watches on straps around their wrist, but men wore their pocket watches on a chain, and they kept their pocket watches in their vest pocket of their suit.
During the early twentieth century, when a man was asked what he thought about wearing a watch on his wrist (known at the time as a wristlet) one man remarked he wouldn't be caught doing such an unrefined thing. He said you would be as likely to catch him in a dress as you would wearing a "wristlet."
When you examine these first generation wristwatches, with the skinny strap, you can kind of understand why men would have thought they were feminine at the time.
When men went to fight in World War I, having a timing tool on their person, to synchronize events, became invaluable. The challenge was if you were a soldier living and fighting in a trench, and you had to keep your pocket watch in your vest, and it was freezing cold in the trench, in order to time events, you would have to take-off your gloves, unbutton your trench-coat, unbutton your coat and reach in your pocket, while holding your rifle in the other hand. This process was clumsy, laborious and time-consuming.