required the prop to be swung from alongside the fuselage. The nacelle was hinged at the bottom to provide some access to the engine for maintenance, but this was insufficient, and additional sliding panels were added to the sides of the fuselage. A mesh screen behind the observer was intended to prevent propeller strikes. The first prototypes were unarmed, but the production S.A was soon eclipsed by more conventional fighter, such as the Nieuport 10 and Nieuport 11. Aside from the unorthodox configuration, the aircraft was of standard wood and fabric construction for the period. The wings had a single bay, but to prevent the long flying and landing wires from vibrating in flight, light vertical struts were added mid-bay to brace the wires, giving the aircraft the appearance of a two-bay biplane, much as was done for the later, more conventional SPAD S.VII and SPAD S.XIII single-seat fighters. The SPAD S.A.2 was an improved version of the S.A.1 which first flew on 21 May 1915. The S.A-2's 110 hp engine frequently suffered from overheating, so the design reverted to the S.A-1s 80 hp Le Rhone in the S.A-4, with the same engine being retrofitted to some S.A-2s. Other changes included dispensing with the lower ailerons on the narrower chord lower wings and a larger tailplane to eliminate the need for a bungee to help with trimming. Russian models had minor structural differences to the top wing, incorporating a separate center section rather than each wing panel being joined along the centerline. In spite of its lack of success, the design brought valuable experience to Béchereau and his team. The successful S.VII fighter was a direct development of the A series. It had much in common. However, the differences included the pulpit being dispensed with, being re-engined with a Hispano-Suiza V8, having a delta-shaped tailplane, the fuselage being fitted with additional fairing stringers, wire trailing edges, reduced rib spacing, and proportions adjusted slightly. Most other design details were retained. Operational history The S.A had a short and inauspicious career in the French Aviation Militaire, and it was quickly replaced in service by less dangerous aircraft. Contemporary sources indicate that it was seldom used. Few details are available concerning the careers of the 42 S.A-2 airframes delivered, and it never supplied the entire equipment of an escadrille. The Imperial Russian Air Service operated the SPAD S.A-2 and S.A-4 for a longer