VAK stands for the German equivalent of VTOL/reconaisannce/strike fighter and the 191B was intended to operate after a Soviet first strike on West German airfields. The type was intended to eventually serve as a replacement for the Fiat G.91 but, after suffering from a protracted development cycle, the focus of programme development was changed to test-fly a limited number of prototypes, using the VAK 191B effectively as a technology demonstrator and experimental aircraft for VFW. A total of 91 flights were performed prior to the retirement of all three prototypes in 1975.