In July 1939 the RLM issued a technical specification that eventually became known as Bomber B, a wide-ranging and technically difficult requirement that was intended to lead to a bomber of advanced design but which caused millions of marks and man-hours to be wasted. Features were to include two of the extremely powerful new engines (2,500hp class) then on testbed, remotely sighted defensive cannon barbettes, a pressure cabin, and the ability to make dive-bopmbing attacks. The Ar 340 and Do 317 were rejected or suspended and the Fw 191 and Ju 288 ordered as prototypes.

Focke-Wulf's design team un E. Kösel chose the six-bank Jumo 222 engine, but accepted the lower-powered BMW 801 radial to get the first V1 prototype into the air. A source of trouble was soon identified in the Multhropp wing flaps which also served as the dive brakes; they fluttered severely. Another was the extremely complicated all-electric nature of the Fw 191, and a third was with the 801 engines it was dangerously underpowered.

Eventually the 191B switched to the Daimler-Benz DB 610 double engine, of 2,870hp, and a heavier armament of six MG 151 and four 13mm MG 131 in four fuselage barbettes, but lack of suitable engines was one of the reasons for dropping the whole programme in 1943.

Sources:
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London