Bicorne is the historical hat of the European and American armed forces. One of the most famous wearers of this hat was Napoleon Bonaparte. The best way to describe the shape of this hat is by calling it a fan-shaped hat.
The hat had a wide brim, and the front and the back were folded and pinned together, giving it its distinctive semicircular shape. Specifically, the cap was worn in a side-to-side manner. Some Bicornes were unstructured and, therefore, could be folded easily and tucked under the arm if not worn.
Bicorne has lost its prominence since WWII but is still used in period theatrical performances and movies.