Which World War II military product's distinctive design was so iconic that its manufacturer trademarked the shape in 1949, leading to numerous civilian product adaptations?

Throughout history, military equipment manufacturers have created products that became legendary not just for their battlefield performance, but also for their distinctive designs. Some of these designs were so successful they transcended their military origins to become cultural icons. This trivia question explores one of the most recognizable military product designs that later influenced civilian markets and popular culture. Test your knowledge of military product design history!

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The Zippo lighter, used by US forces
The Jeep Willys MB vehicle
The M1 Garand rifle
The P-51 Mustang aircraft's silhouette