The Boeing XF6B-1 / XBFB-1 was Boeing's last biplane design for the United States Navy. Only the one prototype, Model 236, was ever built; although first flying in early 1933, it rammed into a crash barrier in 1936 and the design was not pursued further.
Ordered by the Navy on 30 June 1931, the plane was a derivative of the F4B; it was almost entirely of metal construction, with only the wings still fabric-covered. It was powered by a 625 hp Pratt & Whitney R-1535-44 Twin Wasp engine.
The intended role of this design turned out to be uncertain. While its rugged construction was capable of withstanding high g-forces, it weighed in at 3,704 pounds (700 pounds more than the F4B), and did not have the maneuverability needed in a fighter aircraft. It was, however, suitable as a fighter-bomber, and in March 1934 the prototype was redesignated XBFB-1 in recognition of its qualities. Even so, various ideas were tried to improve its fighter qualifications, such as an improved engine cowling, streamlining around the landing gear, and even a three-bladed propeller (two-bladed props being standard). Performance remained unsatisfactory and the Navy instead bought the F11C Goshawk.