Accordingly, a pair of prototype aircraft, known as the "VJ 101 C", were developed; these were powered by the lighter RB145 turbojet engine, which was mounted in swivelling nacelles instead. However, development of the VJ 101 C would not be straightforward; one major complication was the changing requirements of the BMVg, who decided to switch the aircraft's envisioned mission profile from the interceptor role to a more general fighter instead, which imposed a requirement for it to be capable of longer low altitude flight endurance, amongst other performance attributes. The new proposal had merged the characteristics of earlier Bölkow, Heinkel and Messerschmitt designs into a sleek, streamlined platform. The VJ 101 C bore some similarities in appearance to the American Bell XF-109, both aircraft having a comparable configuration in terms of possessing paired engines fitted within swivelling nacelles which were positioned at their wingtips. In addition to the wingtip engines, two further lift jets were installed within the fuselage, which functioned to supplement the main engines during hovering flight.