The B-29 Superfortress, Boeing Model 345, can truly be called the miracle aircraft of World War II. No other major combat model, regardless of size, had a short an interval between first between first flight and first appearance over enemy territory-20 months. Once the design was completed and ordered into production, new factories were built. The first to the three prototypes flew on 21 September 1942. To accomplish this feat, the world’s greatest subcontracting network was established to provide materials, equipment, and sub-assemblies. Massive civilian and military-training programs were developed at the same time.