came following the emergence of the Albatros D.II, which entered service with Imperial Germany around this same time frame, which threatened Allied aerial supremacy. In February 1917, the War Office agreed to exchange its Triplane orders for the Admiralty's SPAD S.VII contracts. While both Sopwith and Clayton & Shuttleworth successfully fulfilled their RNAS production orders, Oakley, which had no prior experience building aircraft, delivered only three Triplanes before its contract was cancelled during October 1917. For unknown reasons, the RFC Triplane contract issued to Clayton & Shuttleworth was simply cancelled rather than being transferred to the RNAS. Total production of the type amounted to 147 aircraft. Design The Sopwith Triplane was a single seat fighter aircraft; it shared a considerable amount of its design features, such as its fuselage and empennage, with those of the earlier Pup. While the fuselage was structurally similar, Bruce notes that there were several areas of differences present. One example was the attachment points present for the center wings, which were carried upon the top and bottom longerons of the fuselage and in turn also attached to the center-section struts. One innovation that was present only on the Triplane was the use of single broad-chord interplane struts, which ran continuously between the lower and upper wings. The most distinctive feature of the Triplane is its three narrow-chord wings; these provided the pilot with an improved field of view. These wings had the same span as that of the Pup, while being only 21 square feet less in terms of area. Ailerons were fitted to all three wings. The relatively narrow chord and short span wings have been attributed with providing a high level of manoeuvrability. The introduction of a smaller 8 ft span tailplane in February 1917 was attributed with improved elevator response. The original tail assembly was identical to the Pup's, other than the inclusion of the variable incidence tailplane, which could be adjusted so that the aircraft could be flown hands-off. The Triplane was initially powered by the 110 hp Clerget 9Z nine-cylinder rotary engine. However, the majority of production examples were instead fitted with the more powerful 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 only seeming benefit being a slight increase in its rate of climb. Operational history Introduction