Which innovative store layout feature was first introduced in Army PX (Post Exchange) stores during the Vietnam War era that revolutionized military retail?

Military exchanges (PX/BX) have a fascinating history of serving military personnel worldwide. These retail operations have evolved dramatically from simple supply points to modern shopping complexes. This trivia explores how military retail operations adapted their store layouts to meet the unique needs of service members throughout history, reflecting both military necessity and changing retail practices.

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Self-service layouts that allowed troops to shop without clerks, modeled after civilian supermarkets
Mobile retail trailers that could be quickly repositioned based on troop movements
Catalog-only ordering systems with central warehousing to reduce frontline retail footprints
Regional specialization zones featuring local products from host nations