At Cazaux airfield near Bordeaux was offered by the French Government. Both French Air Force and Dassault personnel were at the airfield along with the Fairey team. Forty-seven low-level supersonic flights took place over a period of two months. It was no coincidence that Dassault had their engineers at Cazaux as they, like Fairey, were interested in delta wing fighters and during the FD.2s tests they learned much about the characteristics of supersonic delta wings. Two days after the FD.2 had returned home the first Mirage III prototype was rolled out.

As Marcel Dassault, the founder of the company, said in the book Mirage, Warplane of the World, "If it were not for the clumsy way in which you tackle things in Britain, you could have made the Mirage yourselves". The first major production model of the Mirage series, the Mirage IIIC, first flew in October 1960. The IIIC was largely similar to the IIIA, though a little under a half meter longer and brought up to full operational fit. The IIIC was a single-seat interceptor, with an Atar 09B turbojet engine, featuring an "eyelet" style variable exhaust.

The Mirage IIIC was armed with twin 30 mm DEFA revolver-type cannon, fitted in the belly with the gun ports under the air intake. Early Mirage IIIC production had three stores pylons, one under the fuselage and one under each wing, but another outboard pylon was quickly added to each wing, for a total of five. The outboard pylon was intended to carry an AIM-9 sidewinder air-to-air missile, later replaced by the Matra Magic.

Although provision for the rocket engine was retained, by this time the day of the high-altitude bomber seemed to be over, and the SEPR rocket engine was rarely or never fitted in practice. In the first place, it required removal of the aircraft's cannon, and in the second, apparently it had a reputation for setting the aircraft on fire. The space for the rocket engine was used for additional fuel, and the rocket nozzle was replaced by a ventral fin at first, and an airfield arresting assembly later.

A total of 95 Mirage IIICs were obtained by the French Air Force (Armée de l'Air, AdA), with initial operational deliveries in July 1961. The Mirage IIIC remained in service with the AdA until 1988.

The Armée de l'Air also ordered a two-seat Mirage IIIB operational trainer, which first flew in October 1959. The fuselage was stretched about a meter (3 ft 3.5 in) and both cannons were removed to accommodate the second seat. The IIIB had no radar, and provision for the SEPR rocket was deleted, although it could carry external stores. The AdA ordered 63 Mirage IIIBs (including the prototype), including five Mirage IIIB-1 trials aircraft, ten Mirage IIIB-2(RV) inflight refueling trainers with dummy nose probes, used for training Mirage IVA bomber pilots, and 20 Mirage IIIBEs, with the engine and some other features of the multi-role Mirage IIIE. One Mirage IIIB was fitted with a fly-by-wire flight control system in the mid-1970s and redesignated Mirage IIIB-SV (Stabilité Variable); this aircraft was used as a testbed for the system in the later Mirage 2000.

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