Which revolutionary retail innovation was first widely implemented by the U.S. military during WWII before transforming civilian retail operations globally?

Throughout military history, innovation in retail and supply chain management has been critical to battlefield success. From Napoleon's famous quote that 'an army marches on its stomach' to modern military PX systems, retail innovation has shaped how armed forces equip and sustain themselves. This trivia question focuses on a groundbreaking retail innovation that transformed military supply chains and influenced civilian retail practices worldwide.

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Self-service shopping (allowing customers to select their own merchandise without clerk assistance)
Standardized barcoding system for inventory tracking
Point-of-sale computerized cash registers
Customer loyalty program with tiered benefits