The Sopwith Triplane was a British single seat fighter aircraft designed and manufactured by the Sopwith Aviation Company during the First World War. It was the first military triplane to see operational service. The Triplane joined Royal Naval Air Service squadrons in early 1917 and was immediately successful. It was nevertheless built in comparatively small numbers and was withdrawn from active service as Sopwith Camels arrived in the latter half of 1917. Surviving Triplanes continued to serve as operational trainers until the end of the war.
The Triplane began as a private venture by the Sopwith Aviation Company. The fuselage and empennage closely mirrored those of the earlier Pup, but chief engineer Herbert Smith gave the new aircraft three narrow-chord wings to provide the pilot with an improved field of view. Ailerons were fitted to all three wings. By using the variable incidence tailplane, the aircraft could be trimmed to fly hands-off. The introduction of a smaller 8 ft span tailplane in February 1917 improved elevator response.
The Triplane was initially powered by the 110 hp Clerget 9Z nine-cylinder rotary engine, but most production examples were fitted with the 130 hp Clerget 9B rotary. At least one Triplane was tested with a 110 hp Le Rhône rotary engine, but this did not provide a significant improvement in performance.
The initial “prototype of what was to be referred to simply as the Triplane” first flew on 28 May 1916. The Triplane was very agile, with effective, well-harmonised controls. When manoeuvring, however, the Triplane presented an unusual appearance.