Which military retail innovation was first introduced during World War II that revolutionized how troops accessed consumer goods in combat zones?

Military exchanges and post exchanges (PX) have played a crucial role in military history, serving as retail lifelines for troops worldwide. These unique retail operations have evolved from simple supply posts to comprehensive department stores with global supply chains. This trivia tests your knowledge of how military retail operations have shaped soldiers' experiences throughout history and during major conflicts.

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The Mobile PX (Post Exchange) trucks that followed front lines
Online ordering system via military telegraph
Submarine-based retail outlets for naval forces
Airdropped retail catalogues with mail-order forms