The Boeing B-9 bomber was the earliest plane based on the advanced, extremely aerodynamic Monomail design of 1930 that made traditional biplane construction obsolete.

It had a top speed of 186 mph (299 kph) and could outrun the fighters of the day by 5 mph (8 kph). The monoplane bomber reached this speed even though it had a five-person crew (in open cockpits) and carried a 2,400-pound (1089 kilogram) bomb load.

Boeing built the YB-9 prototype bombers at company expense to show their design potential to the military. The B-9 is recognized as a revolution in bomber design, introducing new structures and aerodynamic concepts including the first use of a servo tab on an American airplane.

The Model 246 was an improved version of the B-9 Bomber. In outward appearance it was nearly identical to its predecessor, but featured improvements such as a higher bomb load capability and faster speed. Its Army designation was Y1B-9A.