The SPAD S.XIII (S.13) was a further development of the successful SPAD S.VII (S.7) design, the latter eventually becoming outclassed by the newer and better German aircraft designs of World War 1. The S.XIII would prove a success for SPAD (Societe Pour l'Aviation et ses Derives), adding yet another fine fighter aircraft to its resume and a formidable platform to the conflict. The S.XIII featured an increased wingspan, more powerful engines and dual machine gun systems along with more subtle changes in design over the S.VII. In the end, over 8,400 examples would roll off the assembly lines.
Configuration of the S.XIII was similar in most respects to the S.VII before it. The pilot, wings, landing gear and engine were all mounted to the forward end of the fuselage. Construction was of an internal wood structure with a fabric covering along with light alloy used near the engine area. The biplane wings were of equal span, with the lower component aligned directly with the upper. The pilot sat to the rear of the upper wing assembly in an open-air cockpit with a forward view overlooking the twin 7.7mm Vickers machine guns - these synchronized to fire through the spinning propeller via an interrupter gear. The S.XIII achieved first flight on April 4th, 1917 and was in operational service along the frontlines by May of that year.
In combat, the S.XIII proved its worth (and pedigree for that matter). The aircraft was able to out-fly the German D.VII types well enough and compared favorably to even the fabled Sopwith Camel. Structurally, the S.XIII was sound enough to withstand a good deal of punishment before inevitably giving in. This structural integrity generally made diving a supreme tactic for S.XIII users. If the design sported any major flaw it was in its reduced maneuverability at slower speeds - this alone led to dangers in both combat and in bringing the aircraft in for a landing.
Nevertheless, the S.XIII proved a popular mount for allied aces including American Eddie Rickenbacker and Frenchmen Rene Fonck and Georges Guynemer (Guynemer personally making a case for an improved S.VII, eventually leading to the development of the S.XIII). The type served with air forces across the globe even in the post-war years.
Like the S.VII before it, the S.XIII was designed by Louis Bechereau.