Which military retail innovation was first implemented during World War II and revolutionized supply chain management for troops in combat zones?

Military exchanges (PX/BX stores) have a fascinating history in retail supply chain management, serving military personnel worldwide for centuries. These unique retail establishments have evolved from simple sutlers' wagons following troops to sophisticated global retail operations with billions in annual sales. They provide tax-free goods, support military families, and generate funds for MWR (Morale, Welfare, and Recreation) programs. How well do you know the history of military retail operations?

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The Ship's Store Ashore program
The K-ration retail exchange system
The Army Exchange Service mobile PX trucks
The Navy's floating retail stores (FRS)