The C.860 was ordered by the French Air Ministry who planned to use it, piloted by André Japy, for rapid long distance communications. Powered by a Renault 6Q-03 engine, it had a range of up to when cruising at . It was also expected to set distance and altitude records in Category 1 with a Renault engine and in Category 2 with a Renault, but war intervened. Its wing and empennage were aerodynamically similar to those of the Caudron Simoun, though the single-piece wing was structurally closer to that of the record-setting Rafale racer. The wing was tetragonal in plan, with more sweep on the trailing edge than on the leading edge, though the tips were semi-elliptical. It had an all-wood structure with a single box spar which incorporated an upper flange of gumbo-limbo, a Central and South American wood of particularly high bulk modulus, together with spruce and plywood ribs. The ply skin was finished with a fabric overlay. Its ailerons were carried on auxiliary spars. The C.860's fuselage was slender, with a maximum width of only and about one third of it ahead of the wing leading edge. Its air-cooled six-cylinder Renault 6Q-03 inverted in-line engine, supercharged to , was in the nose with its main and collector fuel tanks behind it over the centre of gravity. Together with four smaller wing tanks, these gave a fuel capacity of . The pilot had an enclosed cockpit with his head raised only slightly above the fuselage under a shallow canopy with a horizontal strip of plexiglas for forwards and sideways vision, a solid top and an extended fairing aft. There were also windows in the fuselage sides for downward views. The fuselage had a wooden frame with canvas covered sides and curved magnesium sheet top and bottom. The empennage of the C.860 was conventional, with a straight-tapered, blunt-tipped horizontal tail carrying separate elevators. The tall vertical tail had a similar shape though, unlike the elevators, the rudder was balanced. The aircraft had a fixed, tailwheel undercarriage with a track. Messier oleo strut landing legs were mounted on the wing spar. Legs, mainwheels and the steerable tailwheel, also on an oleo strut, were enclosed in fairings. By 5 September 1938 the C.860 had been brought, still not quite complete, from the Caudron factory at Issy-les-Moulineaux to the airfield at Guyancourt.