On this day, in 1955, the MD 550 made its first flight at Melun-Villaroche with Roland Glavany at the controls.
For its first flights, the aircraft had neither after-burners nor rockets. Even with this engine configuration, it reached Mach 0,95 in a dive on its 4th sortie, on July 24. After a brief 6-month period of fine-tuning, it reached Mach 1.3 flying horizontally.
The first series of flight tests gave rise to refinements in the aerodynamic configuration. It was clear that the delta fin would have to be changed to a sweptback fin. The side-by-side twin engine configuration also posed some development problems; flanges were added to the rear fuselage, thereby changing the curvature.
Alteration work was completed at the beginning of May 1956. With its new sweptback fin (called the F fin) and its modified servo actuator for the elevons, the aircraft was ready to fly again. The MD 30 R engines were fitted with after-burner jet pipes, bringing the unit thrust to 1,000 kg. Finally the aircraft was equipped with an independent dual liquid SEPR 66 booster rocket providing 1,500 kg of thrust over 80 seconds. In order to adapt the aircraft to high Mach speeds and to the Viper reheat engines, the air intakes were redesigned with a smaller cross-section. These alterations made the aircraft heavier, bringing its total empty weight to 3,610 kg. The modified aircraft flew again on May 5, 1956, using for the first time, its after-burners. The MD 550-01 was renamed Mirage I and the MD 550-02 Mirage II.