Which military retail innovation was first introduced during World War II and revolutionized how troops accessed products in combat zones?

The Post Exchange (PX) and similar military retail systems have been crucial to troop morale and military operations for centuries. These unique retail environments have evolved from simple sutlers' wagons following armies to sophisticated global retail operations with billions in revenue. This poll explores the fascinating corporate history of military retail systems that have supported forces worldwide through wars and peacetime alike.

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The Mobile PX (Post Exchange) truck system that brought supplies directly to forward operating areas
The Military Scrip currency system that eliminated the need for soldiers to carry national currencies
The Ship's Service store concept that created permanent retail facilities on naval vessels
The Catalog Order System allowing soldiers to order items from home country retailers for delivery to the front