In March of 1938, in an attempt to remedy some of the deficiencies of the basic design, the Boeing company offered a more advanced version of the XB-15. It was known by the company as the Model 316, and was approximately the same size as the XB-15. However, in an attempt to provide more power, the Model 316 was to have been powered by four 1400 hp Pratt & Whitney R-2180 Twin Hornet air cooled radials.
The Model 316 was offered to the Army in several different forms. The Model 316D version, which featured a high-winged design with an 80,000 pound gross weight, 152-foot wingspan, seven machine guns, and a pressurized canopy, attracted sufficient attention so that two examples were ordered by the Army in June of 1938 under the designation Y1B-20.
Shortly after the order, the Army concluded that the Y1B-20 was simply too expensive and that they really did not require bombers with range or carrying capability beyond those of the B-17. Consequently, both Y1B-20 prototypes were cancelled before anything could be built.
Specification of the Boeing Y1B-20:
Four Pratt & Whitney R-2180 Twin Hornet air cooled radials, rated at 1400 hp each. Weights: 80,000 pounds gross Dimensions: wingspan 152 feet Armed with seven machine guns.