• The Mirage III was one of the most successful aircraft ever created in French aero-industry

The Mirage III family grew out of French government studies begun in 1952 that led in early 1953 to a specification for a lightweight, all-weather interceptor capable of climbing to 18,000 m (59,040 ft) in six minutes and able to reach Mach 1.3 in level flight.

Dassault's response to the specification was the Mystere-Delta 550, a sporty-looking little jet that was to be powered by twin Armstrong Siddeley MD30R Viper afterburning turbojets, each with thrust of 9.61 kN (2,160 lbf). A SEPR liquid-fuel rocket motor was to provide additional burst thrust of 14.7 kN (3,300 lbf). The aircraft had a tailless delta configuration, with a 5% chord (ratio of airfoil thickness to length) and 60 degree sweep.

The tailless delta configuration has a number of limitations. The lack of a horizontal stabilizer means flaps cannot be used, resulting in a long take-off run and a high landing speed. The delta wing itself limits maneuverability; and suffers from buffeting at low altitude, due to the large wing area and resulting low wing loading. However, the delta is a simple and pleasing design, easily built and robust, capable of high speed in a straight line, and with plenty of space in the wing for fuel storage.

The first prototype of the Mystere-Delta, without afterburning engine or rocket motor and an absurdly large vertical tailfin, flew on 25 June 1955. After some redesign, reduction of the tailfin to more rational size, installation of afterburners and rocket motor, and renaming to Mirage I, the prototype attained Mach 1.3 in level flight without the rocket, and Mach 1.6 with the rocket lit in late 1955.

However, the small size of the Mirage I restricted its armament to a single air-to-air missile, and even before this time it had been prudently decided the aircraft was simply too tiny to carry a useful warload. After trials, the Mirage I prototype was eventually scrapped.

Dassault then considered a somewhat bigger version, the Mirage II, with a pair of Turbomeca Gabizo turbojets, but no aircraft of this configuration was ever built. The Mirage II was bypassed for a much more ambitious design that was 30% heavier than the Mirage I and was powered by the new SNECMA Atar afterburning turbojet with thrust of 43.2 kN (9,700 lbf). The Atar was an axial flow turbojet, derived from the German World War II BMW 003 design.

The new fighter design was named the Mirage III. It incorporated the new area ruling concept, where changes to the cross section of an aircraft were made as gradual as possible, resulting in the famous "wasp waist" configuration of many supersonic fighters. Like the Mirage I, the Mirage III had provision for a SEPR rocket engine.

The prototype Mirage III flew on 17 November 1956, and attained a speed of Mach 1.52 on its seventh flight. The prototype was then fitted with the SEPR rocket engine and with manually-operated intake half-cone shock diffusers, known as souris ("mice"), which were moved forward as speed increased to reduce inlet turbulence. The Mirage III attained a speed of Mach 1.8 in September 1957.

The success of the Mirage III prototype resulted in an order for 10 preproduction Mirage IIIAs. These were almost two meters longer than the Mirage III prototype, had a wing with 17.3% more area, a chord reduced to 4.5%, and an Atar 09B turbojet with afterburning thrust of 58.9 kN (13,230 lbf). The SEPR rocket engine was retained, and the aircraft were fitted with Thomson-CSF Cyrano Ibis air intercept radar, operational avionics, and a drag chute to shorten landing roll.

The first Mirage IIIA flew in May 1958, and eventually was clocked at Mach 2.2, making it the first European aircraft to exceed Mach 2 in level flight. The tenth IIIA was rolled out in December 1959. One was fitted with a Rolls-Royce Avon 67 engine with thrust of 71.1 kN (16,000 lbf) as a test model for Australian evaluation, with the name "Mirage IIIO". This variant flew in February 1961, but the Avon powerplant was not adopted.