Celebrated officers wore the feathered crowns of egrets. British infantrymen wear “hackles.” Italian shock troops, known as Bersaglieri, rather flamboyantly sport the feathers of a particular wood grouse known as a capercaillie.

Military tradition has spawned a bizarre menagerie of headgear, both for dress occasions and battle. The practice is virtually as old as warfare. It knows no borders and, at times, it seems to defy logic...