Which WWII-era military product innovation was originally code-named 'Variable Time Fuse' but later revolutionized civilian technology after declassification?

Throughout history, wartime necessity has driven remarkable product innovations that later transformed civilian markets. From radar technology to jet engines, military R&D has shaped countless everyday items we now take for granted. This trivia question explores one of the most influential product development stories from World War II that revolutionized both military capability and later became essential in civilian sectors. Test your knowledge of how military necessity drives innovation!

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Miniature proximity radar systems (precursor to modern motion sensors)
Self-sealing fuel tanks (foundation for modern automobile safety systems)
Synthetic rubber compounds (basis for modern athletic footwear)
Pressurized aircraft cabins (template for modern HVAC systems)