Airmen flying out of Italy received "invasion money" when they were paid by the American government. The money became the medium of exchange and was accepted by the Italians. What choice did they have?  One lira was equal to one penny; one hundred lire was equal to one dollar, etc., 

When in England, American soldiers were paid in the standard English money. The pound note was equal to $4.03 in American currency at that time.