Zipperhead

Military slang for someone who operates tanks or other armoured treaded vehicles. Many tankers over the course of their career will bang their heads on something as the tank moves over uneven terrain; after the cut is sewn up it resembles a zipper on their head. This was so common during the Great War that the GA Tank Troops instituted the beret as their official headgear. This led the to the other ground branches adopted distinctive headwear, as well; the Regulars adopted a combination cap, the artillery adopted a tall conical hat, and the Grenadiers adopted the helmet.