Which of these military products was developed in the shortest time from concept to deployment during WWII, revolutionizing product development timelines in the defense industry?

During World War II, military product development accelerated dramatically, with numerous innovations emerging under intense pressure. Many of these developments changed not just the course of the war but influenced post-war consumer technology. This trivia question focuses on a critical innovation that represented a major turning point in military technology development. Test your knowledge of how emergency wartime needs drove unprecedented product development timelines and solutions.

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The Manhattan Project's atomic bomb (6 years from theoretical concept to deployment)
The P-51 Mustang fighter aircraft (117 days from contract to first prototype flight)
The M1 Garand rifle (8 years from initial design to standard issue)
The Liberty Ship cargo vessel (1 year from design approval to first completed ship)