Challenge coins were never officially sanctioned, so the history behind the tradition is widely debated among military historians.

A common narrative purports that a wealthy American lieutenant in World War I distributed matching bronze coins to his unit members before they were deployed. When an American fighter pilot was captured by Germans and escaped to a French outpost, he was assumed to be a German spy — until he presented the challenge coin around his neck. According to the tale, the coin saved his life — and earned him a bottle of French wine as reparation.

Other historians believe the tradition began in an infantry-run bar in Vietnam, where patrons were required to present enemy bullets or their challenge coin upon entrance.

In keeping with either narrative, challenge coins still earn service members their share of alcohol. Military members often tap their challenge coins upon meeting in a bar — shouting, “Coin check!” — and anyone who either cannot produce one or is the last to show it buys the first round of drinks.