Which of these military product innovations was marketed with the famous slogan "The Weapon That Won The War" despite being initially rejected by the U.S. military?

Throughout history, military technology and product innovations have dramatically altered warfare strategies and outcomes. Some military products became so iconic they changed the course of conflicts and were marketed with memorable campaigns. This trivia question focuses on a famous military product innovation that was heavily marketed during World War II, demonstrating the intersection of military necessity, industrial production, and advertising genius.

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M1 Garand rifle
Jeep (Willys MB)
M3 "Grease Gun" submachine gun
M1 Carbine