Which military branch first established the formal Post Exchange (PX) system that revolutionized military retail in the late 19th century?

The Post Exchange (PX) system has been a crucial part of military life for generations, providing goods and services to service members and their families worldwide. These retail establishments have evolved from simple trading posts to modern department stores, with a fascinating history of supporting troops and boosting morale. Test your knowledge about this unique military retail institution that has shaped the shopping experience for millions of military personnel.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

U.S. Army
U.S. Navy (who called them Ship's Stores)
U.S. Marine Corps
U.S. Air Force (originally as part of the Army Air Corps)