On early J79 installations (F-104, F-4, A-5 Vigilante) actuation of the secondary nozzle was mechanically linked to the afterburner nozzle. Later installations had the final nozzle mechanically actuated separately from the AB nozzle. This gave improved efficiency (better match of primary/secondary exit area with high Mn <Mach number> requirement) at Mach 2 (B-58 Hustler) and Mach 3 (XB-70).[12]