Which of these WWII-era military products became so iconic that original examples now sell for thousands of dollars at auction, with the company later releasing civilian versions that became retail successes?

Throughout military history, certain products have become iconic symbols of their era, changing the course of conflicts and becoming legendary in their own right. These items often transcended their military purpose to become cultural touchstones and collectors' items. This trivia question focuses on one such famous military product that revolutionized battlefield communication and later became highly sought after by collectors.

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The Zippo lighter, with its windproof design and lifetime guarantee, originally created for U.S. troops in WWII
The M1 helmet, which replaced the British-style 'Brodie' helmet and remained in U.S. service until the 1980s
The Parker 51 fountain pen, designed for military officers to function in varying altitudes and climates
The Elgin A-11 wristwatch, known as the 'Watch that Won the War' for its reliability under combat conditions