According to aviation historian Michel van Pelt, French Air Force officials were against a pure rocket-powered fighter, akin to the wartime-era Messerschmitt Me 163 Komet, but instead favoured a mixed-propulsion approach, using a combination of rocket and turbojet engines.

During 1944, a new company, Société d'Etudes pour la Propulsion par Réaction (SEPR), had been founded for the purpose of developing France's own domestic rocket engines.

The combination of Furaline, which was relatively difficult to manufacture in comparison to conventional kerosene, and nitric acid functioned as a hypergolic propellant, not requiring any igniting agent.

Amongst the specified requirements given were the ability to attain Mach 1.3, a relatively high climb rate, and the possibility of deploying the aircraft from austere airstrips.

[5] The Trident was a fast-looking bullet-shaped aircraft, furnished with an aerodynamically clean fuselage and thin, straight wings in order to minimise drag.

All three tail surfaces were all-moving, eliminating the requirement for separate elevators and rudders while preventing control lock-ups during high speeds.

[4] On 2 March 1953, the first prototype Trident I conducted the type's maiden flight; flown by test pilot Jacques Guignard, the aircraft used the entire length of the runway to get airborne, being powered only by its two 4 kN (900 lbf) Turbomeca Marboré turbojet engines.

[7] According to aviation historian Bill Gunston, the early test flights of the SO.9000 were "hairy" prior to the installation of the rocket motor[2] in September 1954.

During the first flight of the second Trident I prototype on 1 September 1953, the aircraft crashed after struggling to gain altitude after takeoff and collided with a utility pole, resulting in the separation of the nose section and Guignard sustaining severe injuries.

Powered by these engines, the aircraft soon proved its ability to exceed Mach 1 during a shallow dive even without the added thrust of the rocket motor.

According to Pelt, the French Air Force were impressed by the performance of the Trident, and were keen to adopt an improved operationally-capable model into service.

A third prototype had been built by SNCASO to develop a surface-to-air missile based on the Trident, but it was purchased by the Air Force to replace the destroyed aircraft and first flew on 30 March.

None of these later accomplishments were publicised to avoid upsetting the Air Force after it had decided upon the Dassault Mirage III to satisfy its interceptor requirement.

[14] The fourth incomplete pre-production aircraft would have served as a prototype for the Trident III family, all of which would have been fitted with two afterburning Turbomeca Gabizo turbojets and a SEPR 631.