Before the air defense missile proliferated the battlefields of the Cold War, it was left to aircraft designers to develop products capable of reaching - and ultimately destroying - incoming enemy bombers in time. During the 1950s, the enemy of the West had become the Soviet Union and that nation possessed nuclear-capable bombers able to reach all points in Europe. As such, the West invested heavily in airspace deterrents through combat aircraft capable of meeting the aerial threat head-on - the "interceptor".
About this time, the French Air Force - rebuilding after its fall from grace during the German occupation of World War 2 (1939-1945) - called for a new single-seat supersonic interceptor capable of Mach 1 speeds. It was to operate exclusively against enemy bombers at altitudes nearing 50,000 feet. Much of the requirement was influenced by what was seen in the first "jet-versus-jet" duels of the Korean War (1950-1953) and furthermore the product was to be of wholly-French design, development and production.
SNCASO, founded in 1936 from the merger of aero-concerns Bleriot, Bloch, Liore et Olivier and others, stood much to gain from the exercise when the company was commissioned to fulfill the French Air Force requirement. Engineers elected for a combination/mixed powerplant scheme made up of a pair of turbojet engines and a rocket booster to supply s lightweight airframe the needed performance. The turbojets would act as supplementary power to the primary rocket motor fit.
NOTE: This approach to combat warplane propulsion was somewhat a common avenue during the 1950s as a turbojet engine, in and of itself, lacked the outright performance due to the infant technology at work - as such they were frequently fitted in pairs or coupled with rocket motors for improved speeds.
The aircraft's shape was well-streamlined from nose-to-tail. The cockpit, heavily framed, was featured aft of a long, slim nosecone assembly. The tail unit encompassed a single vertical plane with low-mounted horizontal planes and were hydraulically-boosted with an "all-moving" quality about them. The wing mainplanes were straight, thin and mid-mounted along the fuselage sides. At each wing tip was seated one of the aforementioned turbojets with the rocket being placed within the aft section of the tubular fuselage. The fuselage also carried the fuel stores for both engines as well as the retractable tricycle undercarriage which was reinforced for rough-field operations.
The original turbojet engines under consideration were 2 x Turbomeca "Marbore II" centrifugal flow units of 882lb thrust each. The liquid-fueled (triple chamber) rocket motor component selected was a Model 481 9,920lb-output system from SEPR. Unlike the turbojets, the rocket motor had only a fuel supply allowing it to last just a few minutes.
On April 8th, 1951, the French Air Force committed to a pair of flyable prototypes under the designation of SO.9000 "Trident". A first-flight then followed on March 2nd, 1953 though only under the power of the wingtip turbojets. The aircraft was debuted to the public that summer (June) at the Le Bourget Air Show. The second prototype was set for its first-flight in September 1953 but the specimen clipped a pole on its first take-off which resulted in a non-fatal crash.
On September 4th, 1954, the Trident finally went airborne with its entire powerplant scheme in place but the rocket motor failed the following month, subsequently grounding the aircraft pending a formal review.
As tested the SO.9000 had an empty weight of 7,400lb with a gross weight nearing 12,125lb. Maximum speed reached was 1,061 miles per hour (Mach 1.6). Dimensions included a length of 45.10 feet, a wingspan of 26.8 feet and a height of 10.4 feet.
Engineers reassessed their aircraft and elected to fit 2 x Dassault MD.30 turbojets to the wingtips instead of the original Turbomeca pairing - these engines were nothing more than license-produced forms of the British Armstrong-Siddeley "Viper" (ASV.5) series turbojets outputting 1,642lb of thrust. A first-flight with the new turbojets took place on March 17th, 1955 and proved more than successful as the desired performance increase was finally had. The following month, the aircraft achieved Mach 1+ speeds in level flight under power of the turbojets alone. With the rocket engaged, the aircraft boosted performance even more.
These early prototypes marked just one phase of two major phases in the Trident program. As such, on December 10th, 1956, the line was ended as the aircraft had achieved their goals for the most part. This opened a path to development of a more advanced form in the SO.9050 "Trident II" (commissioned back in 1954) and this model would better serve in showcasing the speedy platform as a true combat warplane.
The new design initiative carried over many of the strong qualities of the original Trident. The cockpit was refined and the air brake scheme revised while the wing mainplanes were thinned out and the undercarriage legs lengthened. As an interceptor aircraft, Trident II was slated to carry a weapons load out of air-to-air missiles as well as Air-Interception (AI) radar in the nose so provisions for these were included. One major propulsion change was to the two-chamber SEPR Model 631 series rocket motor promising 6,600lb of thrust.
A first-flight of the refined interceptor was had on July 19th, 1955 and the new rocket motor installation was then tested under flying conditions in December of that year with success. A second prototype followed on January 4th, 1956 but this specimen was lost (non-fatally) to a turbojet flame-out (both engines). A third prototype went airborne on March 30th, 1956 and, that same year, a pre-series contract (eventually to cover ten total aircraft) arrived - these now switching over to the French-made Turbomeca "Gabizo" turbojet of 2,425lb thrust each.
In 1957, SNCASO went defunct by way of merger with Sud-Est and, in its place, "Sud Aviation" was born. That same year (May), one of the SO.9050 prototypes was lost while practicing its routine for the Paris Air Show (the pilot was killed). That same month, a pre-series model went airborne for the first time and, to this point, the interceptor exhibited an excellent rate-of-climb and good performance but was known to suffer in low-altitude control envelopes - nevertheless it was a record-setter for its time.
Despite the program continue to gain maturity and coming through on the promises of performance in the interception role, politics seemingly doomed the program as it was cancelled in full on April 26th, 1958. Those airframes still under construction at the time were dismantled where they sat and sold off. The French Air Force, still in need of an indigenous interceptor, elected for the simpler, single-engine Dassault Mirage (becoming the "Mirage I" in formal service). The remaining, active Trident II forms continued their flying days as research platforms and nothing more with a final flight claiming a world altitude record. One of the examples ended up at the Bourget Museum.
The "Trident III" was a proposed Trident development intended to carry even thinner wings, for higher aerodynamic efficiency, and more powerful turbojet engines intended for March 2+ performance. in addition to this it was to be outfitted with an advanced radar suite in the nose but the proposal fell to naught.