Which retail innovation did the U.S. military first deploy in Iraq in 2003 that revolutionized how soldiers could purchase personal items in combat zones?

Post Exchange (PX) and Base Exchange (BX) stores have been vital to military life for generations, providing goods and services to service members and their families worldwide. These retail operations have evolved significantly since their inception, adapting to changing military needs and retail technologies. This trivia question focuses on a major retail innovation that transformed how military personnel access retail services in combat zones and remote deployments.

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Containerized PX units (nicknamed 'PX in a Box')
Drone-delivered personal supply packages
Mobile PX smartphone app with delivery service
RFID-enabled automated vending facilities