Boeing B-17B/C/D Flying Fortress Early production of B-17 (Incl Bonus Staggerwing, Ryan XFR1 Fireball, Bowlus XCG7)

In 1934, the U.S. Army Air Corps issued requirement for a multi-engined bomber to replace the Martin B-10. Boeing submitted XB-17 to compete with the Douglas B-18 Bolo and Martin Model 146. Although the XB-17 was cashed during flight-test, the Army was impressed in the potential of this new bomber to place order for 13 YB-17 testbed. It became B-17A after testing had finished. In 1938, The Army Air Crops ordered 39 first production model B-17B. As the production line developed, Boeing engineers continued to improve upon the B-17 design. In 1940, The Army Air Crops ordered 38 improved B-17B as B-17C. 20 B-17Cs were transferred to RAF as Fortress I, which used them during the early stage of WWII. The remaining C models were modified to D model, with other 42 D models were ordered. The early B-17 models were proved to be unsuitable for combat use over Europe, until the first mass-production version B-17E entered service in the middle of 1942.