Which of these common products was NOT originally developed for military use before becoming a popular consumer item?

Throughout history, many everyday products we use today originated from military research and development initiatives. These military innovations later found their way into civilian markets, transforming industries and consumer lifestyles. Test your knowledge about the corporate history behind these military-to-civilian product transitions that changed the world of retail and consumer goods.

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Microwave ovens (developed after a Raytheon engineer discovered radar equipment had melted a chocolate bar in his pocket)
Post-it Notes (invented by 3M scientist Spencer Silver while trying to create a super-strong adhesive for aircraft construction)
Duct tape (created for the US military during WWII as a waterproof tape to keep ammunition cases dry)
GPS navigation systems (developed by the US Department of Defense for military positioning and precision targeting)