The First World War was a turning point in the development of watches. Although wrist watches had been invented in the 1860’s as a fashion accessory for ladies, war service quickly made the value of being able to tell time without using your hands apparent to men. Accordingly, all of the clockmakers rushed out a wide variety to market, where they were snapped up quickly. New types of wrist watches were introduced as well; a Cartier best-seller today is a variant of a 1917 model. Read more about this here.
For those who remained attached to their pocket watches, a number of firms began offering wrist bands that could hold a pocket watch. Read more about this here.