Which technological innovation transformed military Post Exchange (PX) retail operations during the Vietnam War era?

The Post Exchange (PX) system has been a crucial part of military life for generations, providing retail services to soldiers in peacetime and war. These retail operations have evolved dramatically with technology and changing military needs. This trivia poll tests your knowledge about the development of military retail technology and its historical significance in supporting troops worldwide.

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IBM's Military Exchange Inventory System (MEIS), which used punch cards to track inventory across remote bases
Polaroid's Field Receipt Technology, which provided instant documentation of purchases for deployed soldiers
The Radio Frequency Combat Retail System, which used early RFID technology for supply chain management
The Tactical Automated Shopping Terminal (TAST), which allowed touchscreen ordering at forward operating bases