The VAK concept of NATO and the German Armed Forces required an aircraft that was able to take off from unprepared airfields without runways. Its mission was close air support. In addition it had to be able to fly long distances in extreme-low-altitude in order to prevent attacks of antiaircraft weapons and radar detection. Because of this the VAK was designed with short wings and a minor extension so it would provide its pilots a tolerable flight and bear aerodynamically difficult extreme-low-altitude-flights. The equipment was stored in a weapon bay.

The first prototype flew on September 10, 1971, the first transition - the transfer of vertical flight in horizontal and vice versa as well as turning off and on the lift-engines - was achieved on October 26, 1972 in Manching, Bavaria, at a speed of 400 km/h.

All three VAK 191B experimental aircraft completed a total of 91 flights that lasted all together 12 hours.