Which famous consumer product was originally developed specifically for U.S. military use in World War II before becoming a household staple?

Throughout history, military equipment and memorabilia have created unique product markets. From WWII ration packaging to modern tactical gear branding, military-related products have distinct marketing approaches and consumer bases. This poll tests your knowledge of the commercial side of military history - where battlefield innovations meet consumer markets.

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Duct tape (originally called 'Duck Tape' and developed for waterproofing ammunition cases)
Zippo lighters (originally designed for Navy personnel to light cigarettes in windy conditions)
Ray-Ban Aviator sunglasses (originally designed for Air Force pilots to reduce glare)
Swiss Army Knife (originally issued to American GIs as a standard field tool)