The British Air Ministry request in 1916 for a single-seat fighter design to be powered by the 150 hp Hispano-Suiza V-8 engine was responded to by a design of H.P. Folland of the Royal Aircraft Factory. The design was conventional with a wire-braced fuselage of a box girder configuration with wooden longerons and spacers. Plywood was applied to the fuselage sides below the engine bearers. The wings had spruce spars and were internally wire-braced. The wings had a single-bay interplane struts. A flat car-type radiator was mounted on the nose. Initial production batch (A4845-A4868) were designated as S.E. 5's. The initial intent was to up grade the design to take the 200 hp geared Hispano-Suiza engine. The second production batch (A8898-A8947) was equipped with the larger engine and became known as the S.E. 5a.

The armament of both aircraft consisted of a Vickers machine gun mounted on the port side of the fuselage and a Lewis machine gun mounted above the center-section of the main plane on a Foster mounting. It has been said that such a configuration was selected based on the input of Capt. Ball whose fighting tactics in his Nieuport was to dive down below an opponent and then lower his Lewis gun to strafe the E.A. from below with the Lewis gun in a vertical position.

The S.E. 5a found an immediate high approval level with its pilots due to its great strength, its splendid view for the pilot, its ease to fly, and its cockpit being warm and comfortable. Many American pilots who served with RFC and RAF squadrons flew the S.E. 5a. Only one A.E.F. Squadron (the 25^th Aero Squadron) was selected to fly the S.E. 5a. However, the Armistice occurred before the 25^th could fly any combat missions (there appears to have been one unofficial mission flown just prior to the armistice).