A process of aerodynamic refinement of the Mystere IVA led to the Mystere IVB, which, in fact, shared only wings, horizontal tail surfaces and main undercarriage members with the earlier model. The Mystere IVB was intended for an afterburning SNECMA Atar 101G axial-flow engine in place of the non-afterburning centrifugal- flow Tay or Verdon. It featured an entirely redesigned fuselage of increased fineness ratio, an upper engine air intake lip for the radar ranging aerial in place of the splitter-plate conical body and a lower-mounted horizontal tail. The first prototype was flown on 16 December 1953 with a Rolls-Royce Avon RA 7R engine developing a maximum afterburning thrust of 4330kg. Two additional prototypes followed, the first of these, powered by the Avon RA 7R, flying on 18 June 1954, and the second, with an Atar 101F-12, flying on 31 March 1955. Of seven pre-series Mystere IVBs completed, the first two each had a SEPR 66 bi-fuel rocket motor to augment the thrust of the Atar 101F engine, and the final two had the Atar 101G-2 engine developing an afterburning thrust of 4500kg. The series Mystere IVB was to have been powered by an Atar 101G-31 rated at 4700kg with maximum afterburning, but the programme was cancelled owing to the superior performance potential of the Super-Mystere B2.