In campaigning for a departure from the Euro, both France's Marine Le Pen and Italy's Beppe Grillo, make the process sound easy. But one does not simply walk out of a monetary union. There are all sorts of messy problems to deal with, including harmful bank runs, massive banknote shortages, and long legal battles with investors over wealth confiscation and the redenomination of debts. I recently stumbled on a successful and rarely-discussed exit from a monetary union: Hawaii in 1942. Hawaii's was a different sort of exit than a potential French or Italian euro exit. Whereas the latter are reactions to being straitjacketed in the face of a slow and grinding recovery from financial crisis, Hawaii's exit was executed in anticipation of a potential military invasion. Despite differing motivations, it's worth investigating the Hawaiian episode to see what it takes to pull off a successful exit. To understand the course of events, I drew on several Fed bulletins from 194...