Which military product development approach was pioneered during WWII and involved gathering direct battlefield feedback from soldiers to rapidly improve weapon designs?

Throughout military history, the development of new weapons and equipment has often followed a product development cycle not unlike modern commercial products. Customer feedback (from soldiers and commanders), prototype testing, and iterative design have been crucial in creating effective military technology. This poll tests your knowledge about a fascinating case study in military product development that changed warfare forever.

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Operations Research - using statistical analysis and mathematical modeling to optimize weapon effectiveness
Command Economy - centralizing all production decisions through military high command without field input
Parallel Development - having multiple companies develop competing versions of the same weapon
Captured Technology Program - reverse engineering enemy weapons to improve domestic designs