Four S.E.4a aircraft were built, being used for research purposes and as home-defence fighters by the Royal Flying Corps.
[3] The wood and fabric single-bay wings, unlike the S.E.4, had noticeable stagger between the upper and lower wings, but were fitted with similar, full span control surfaces which could be moved differentially as ailerons or together as camber changing flaps, to those used on the S.E.4.
[4] The first prototype flew on 25 June 1915,[4] with the remaining three aircraft all having flown by mid August.
[6] The S.E.4a proved easy to fly, demonstrating excellent aerobatic capabilities,[7] but were overweight and underpowered, and was not developed further.
[8] Two of the aircraft, armed with a Lewis gun mounted above the upper wing were issued to Home Defence squadrons of the Royal Flying Corps in the winter of 1915–16, based at Hounslow Heath Aerodrome and Joyce Green.