Focke-Wulf Fw 187 was an intermediate design above the model that was the backbone of which fighting force?
Focke-Wulf Fw 187:  It was conceived by Kurt Tank as a twin-engine, high-performance fighter, but the "Luftwaffe" saw no role for the design, perceiving it as intermediate between the Messerschmitt Bf 109 and Bf 110. Messerschmitt Bf 109: The Messerschmitt Bf 109 is a German World War II fighter aircraft that was the backbone of the Luftwaffe's fighter force.
Luftwaffe