Which revolutionary product design feature was first widely implemented in the P-51 Mustang fighter aircraft during WWII, dramatically increasing its combat effectiveness?

Throughout history, military aircraft design has undergone dramatic transformations to meet the changing demands of warfare. From basic wood and fabric biplanes to advanced stealth fighters, product design in military aviation has been driven by technological innovation, tactical requirements, and lessons learned from combat. This poll tests your knowledge about a significant product design decision that changed the course of military aviation history.

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Laminar flow wing design that reduced drag and increased range
Pressurized cockpit allowing high-altitude operations
Jet propulsion system replacing traditional piston engines
Radar-absorbing materials for stealth capabilities