Which retail technology innovation was first widely adopted by military exchanges (PX/BX) during the Vietnam War era that revolutionized soldier shopping and later influenced civilian retail?

Throughout military history, retail services for troops have evolved dramatically. From the sutlers following armies in the field to modern military exchanges, retail technology has transformed how military personnel access goods. This trivia explores a pivotal retail technology innovation that revolutionized how soldiers, sailors, airmen and marines shopped while deployed - changing military retail history and influencing civilian retail practices.

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Military Exchange Credit Card System (MECCS)
Automated Inventory Tracking System (AITS)
Satellite-based Remote Ordering Terminals (S-ROT)
Biometric Payment Authentication (BPA)