The Boeing B-9 was the first cantilever monoplane bomber to be produced for the US Army. The B-9 began life as the Boeing Models 214 and 215. These were company-funded new bomber designs that were based on the concepts developed by the Model 200 Monomail commercial mail carrier.
Both the Model 214 and the Model 215 were low-winged, all-metal cantilever monoplanes. The fuselage was of semi-monocoque construction, which permitted the use of a more nearly circular cross section. The main landing gear retraced rearward into the engine nacelles, but the lower halves of the wheels remained exposed.
Five crew members were carried--pilot, copilot, nose gunner/bombardier, rear gunner, and a radio operator. Four of the crew members sat in separate open cockpits, widely separated from each other. The bombardier/nose-gunner sat in a cockpit in the nose, which was equipped with a bomb sight and aiming window in the bottom and had a mount for a single flexible 0.30-inch machine gun around the top. Because the fuselage was so narrow, the pilot and copilot sat in separate tandem cockpits immediately behind the nose gunner. A fourth cockpit for a rear gunner was located on top of the fuselage behind the wing. He operated a single flexible 0.30-inch machine gun. The radio operator was located inside the fuselage just ahead of and below the pilot, and had a window on each side of the nose. Because of their wide separation, crew members had difficulty in communicating with each other in flight. The pilot had limited visibility because of the radial engines on each side and the long forward fuselage immediately ahead.
The radial-powered Model 215 was the first to be completed. It took to the air for the first time on April 12, 1931. Since it was a Boeing-owned airplane, it was painted in civilian colors and carried a civilian registration number (X-10633). It was initially powered by a pair of 575 hp Pratt & Whitney R-1830-13 commercial engines. It was tested by the Army on a bailment contract under the designation XB-901. It achieved a maximum speed of 163 mph at sea level.
The B-9 was a truly revolutionary design, and had a speed fully 60 percent greater than that of the Keystone biplane bombers that were still the backbone of the American bomber force in 1932. In war games held in May of 1933, the Y1B-9A could not be intercepted by six Boeing P-12 fighters, giving the USAAAC a bomber with a performance superior to that of its pursuit aircraft. In view of its superior performance, Boeing fully anticipated an Army order for substantial numbers of the new design. However, The Glenn L. Martin company in Baltimore, Maryland had in the meantime brought out a competing design of its own, the XB-907. The XB-907 was even more revolutionary than the XB-901. It was slightly larger than the XB-901 and had a substantially better performance. The Army decided to order the Martin design into production under the designation B-10 and B-12, and no production examples of the B-9 were ordered.
The service of the Y1B-9A was relative short, with all surviving examples being removed from service and surveyed in 1934. So far as I am aware, no examples of the B-9 survive today.