SPAD S . XII The SPAD S . XII or SPAD 12 was a French single - seat biplane fighter aircraft of the First World War developed from the successful SPAD 7 by Louis Béchereau , chief designer of the Société Pour L ' Aviation et ses Dérivés ( SPAD ) . Development . The SPAD 12 was inspired by the ideas of French flying ace Georges Guynemer , who proposed that a manoeuvrable single - seat aircraft be designed to carry a 37 mm cannon , a weapon which had previously been mounted only in large two - seat " pusher " aircraft such as the Voisin III . Béchereau took his own SPAD 7 design as the starting point , but the many major and minor changes incorporated into the SPAD 12 made it a quite different aircraft . The gun chosen for the SPAD 12 was not the old Hotchkiss cannon but a new 37 mm " Semi Automatique Moteur Canon " ( SAMC ) , built by Puteaux , for which 12 shots were carried . The Hispano - Suiza aviation engine had to be geared to allow the gun to fire through the propeller shaft . The SPAD 12 also carried a single 0 . 303 inch ( 7 . 7 mm ) Vickers machine gun mounted on the starboard side of the nose . In order to carry the heavy cannon the airframe was lengthened and the wingspan and wing area increased . The wingtips were rounded rather than squared off and the wings given a slight forward stagger . To accommodate the required geared output propshaft engine , which easily allowed for the hollow propeller shaft for the cannon to fire through , and power the resultingly heavier airframe , 587 kg compared to the 500 kg of the SPAD 7 , the 180 bhp Hispano - Suiza 8 direct - drive Ab engine was replaced by the geared 220 bhp model 8Cb , and gave the SPAD XII a clockwise rotating propeller , as seen from a " nose - on " view . Test flown by Guynemer , the early production models of the SPAD 12 were highly successful after overcoming initial problems with the reduction gear between engine and propeller . Other aces also had success with the new model . However , deliveries were slow , the SPAD 7 and later SPAD 13 having top priority , and even the modest total of 300 aircraft which were ordered were not all completed . Best estimates are only 20 produced . Average pilots found the SPAD 12 a difficult aircraft to master , and the cannon difficult to aim and fire , while manual reloading was difficult . The cockpit filled with fumes upon every firing . Its breech mechanism protruded into the cockpit and prevented the use of a conventional stick to control the aircraft , adding to the difficulties encountered by ordinary pilots . The control setup reverted to a split setup on either side of the pilot , a la Deperdussin . Service . No units were entirely equipped with SPAD 12s . The unknown number of aircraft produced were issued in small numbers , intended for use only by the most skilled pilots , such as Rene Fonck , Lionel de Marmier , Fernand Henri Chavannes , Henri Hay de Slade , Albert Deullin and François Battesti . They were distributed one or two per squadron . Few were delivered to combat units , 8 being recorded on strength in April and again in October ; this may be contrasted with the thousands of SPAD 7s and SPAD 13s in service . Single examples for testing were delivered to the Royal Flying Corps and one to the Aviation Section of the American Expeditionary Force , and reportedly the AEF ' s 13th Aero Squadron got the aircraft , which was given the number " 0 " , and primarily flown by the 13th ' s Charles John Biddle , who ended up with a total of seven confirmed victories in World War I . Six or more are said to have been held by the Red Army .