Boeing YB-9 BomberBoeing YB 9 airplane model. The YB 9 was originally owned, developed and tested by Boeing as the XB 901 (NX10633). The plane was based on the Model 200 commercial transport but was enlarged and adapted to the bomber role. The YB 9 was powered by two Pratt & Whitney R 1860 radial engines which gave it a top speed of 163 mph. Later in its service life, the YB 9 was fitted with the same engines powering the Y1B 9A service test aircraft bringing its top