Which retail innovation dramatically improved supply access for American soldiers during WWII, featuring mobile stores that followed troops across Europe?

The Post Exchange (PX) system has been a critical retail innovation for military personnel since the 19th century. These military-exclusive retail establishments have evolved dramatically over time, adapting to changing warfare conditions, global deployments, and technological advancements. This poll tests your knowledge about a significant retail innovation that transformed how military personnel accessed essential supplies during a major conflict.

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The Mobile Post Exchange (MPX) trucks, which served as traveling department stores for frontline troops
The Victory Box program, which allowed families to ship standardized care packages directly to specific battlefield locations
The Frontline Catalog System, where soldiers could order supplies by radio that would be delivered via dedicated supply planes
The Combat Commissary Cards, which used an early punch-card system to track and distribute rations more efficiently