The term 'hackled headwear' refers to a type of military headgear known as a SHAKO. A SHAKO is a tall, cylindrical hat with a visor and a plume or hackle on top, typically worn by infantry and cavalry units in the 19th century. It was designed to provide protection from the elements and to make the wearer more visible on the battlefield. The SHAKO was eventually replaced by the more practical peaked cap in the early 20th century.