Which military branch's retail system first adopted the name 'Post Exchange' (PX), establishing the term that would later be used across multiple service branches?

The Post Exchange (PX) system has been a cornerstone of military retail for over a century, providing goods and services to service members worldwide. This unique retail ecosystem has evolved from simple sutler wagons following troops to sophisticated global retail operations. Test your knowledge about this distinctive military retail innovation that has shaped both military life and retail history.

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U.S. Army
U.S. Navy (which originally called their stores 'Ship's Service')
U.S. Marine Corps
U.S. Air Force (originally Army Air Corps)