Staff Writer (Updated: 11/20/2015):
Externally, the SPAD S.XII looked every bit as a further development of the SPAD S.VII model. Due to the extra weight imposed on the airframe by the new cannon armament, the fuselage was lengthened over that of the S.VII. A Hispano-Suiza engine was once again used by SPAD and consisted of the 8Bc or 8Bec types, each offering 220 horsepower. What made the 8Bec unique was that the 37mm cannon could be nestled between the cylinder banks. Subtle changes to the wings were also necessitated by the increase in weight.
First flight for the SPAD S.XII was achieved on July 5th, 1917 with limited production examples following. The system proved a handful for the inexperienced but lethal in the hands of a proven military aviator. As the cannon system extended into the cockpit, the aircraft was not controlled through a traditional flight stick. Additionally, reloading the cannon while flying the plane added another responsibility while in-flight. The standard single 7.7mm Vickers machine gun remained a part of the offensive toolbox for the S.XII, a carry-over from the S.VII design.
Though the cannon-mounted SPAD S.XII's initially proved successful, they really required an experienced pilot at the controls of both aircraft and armament. With more and more resources being dedicated to the already proven S.VII and S.XIII designs, the S.XII was limited to a mere 300 production examples and, as such, the system never equipped an entire unit. In any case, the idea of a cannon-armed aircraft was intriguing and perfected to the extreme in the Second World War and beyond.
Like the SPAD S.VII before it and the SPAD S.XIII after it, the SPAD S.XII was designed by Louis Bechereau.