Which retail layout innovation was first widely implemented in military Post Exchanges (PX) during the 1950s before becoming standard in civilian retail?

Throughout military history, Post Exchanges (PX) and Base Exchanges have played a crucial role in troop morale and logistics. These military retail operations have evolved dramatically from simple sutler wagons following armies to sophisticated global retail networks. This trivia question explores how military retail history intersected with a major shift in civilian retail strategy during a pivotal period of military operations.

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Self-service shopping format
Drive-through pickup windows
Membership-based shopping model
Department store layout with specialized sections