[1] The SO.4000 was developed because the French Air Force needed a jet bomber, which produced a specification calling for one after the end of Second World War.
[4] Following the end of the war, the French Air Force produced a requirement for a jet bomber which was expected to have a takeoff weight of roughly 25–30 t (25,000–30,000 kg) and be capable of transonic speeds.
Following a competitive review, SNCASO would receive a development order calling for a pair of manned scale models and a full-sized prototype.
The first scale model, known as the SNCASO M.1, was an unpowered glider which would be tested from atop the Heinkel He 274 V1, (as the French AAS 01A), the first prototype of a late-war high-altitude strategic bomber, which had remained in France after the war.
Both the M.1 and M.2 provided valuable data on features such as swept wings, pilot escape systems, spoiler control, and leading edge slats.
It featured a mid-mounted wing, which was swept at an angle of 35 degrees and mated with a carefully streamlined oval-section fuselage, which was furnished with a relatively tall tricycle undercarriage.
[4] The SO.4000 was operated by a crew of two, consisting of a pilot and test engineer/observer, both of which were seated in a pressurised cockpit located within the extreme nose of the aircraft and covered by a conventional canopy.
[9] Being intended for use as a bomber, the (unbuilt) production aircraft were envisioned to be capable of carrying a bombload of up to 5,000 kg (11,000 lb); furthermore, it was planned to install remotely-controlled barbettes that would have been armed with a pair of 20 mm cannon on the wingtips.
Despite its large size, the SO.4000's total fuel capacity was 1,430 gallons, which would have severely restricted its operational range if the type had ever entered service.