Unlike earlier Sopwith fighters the Dolphin was powered by a static engine, and the deep fuselage virtually filled the gap between the backward-staggered wings so that the pilot sat with his head protruding through a gap in the upper-wing centre section for superb fields of vision in the upper hemisphere. The prototype flew in May 1917 with a 149 kW (200 hp) Hispano-Suiza geared engine, and the same powerplant was used in the Dolphin Mk I that began to enter service late in 1917. Problems with the geared engine then led to the Dolphin Mk III with a direct-drive version of the same engine, and the designation Dolphin Mk II was used for a few aircraft with a 224 kW (300 hp) Hispano-Suiza direct-drive engine. Production totaled 1532, but only 621 were issued to operational squadrons, which disliked the Dolphin’s unusual stalling characteristics and the vulnerability of the pilot in the nose-over landing accident. (Source: The International Encyclopedia of Aircraft, Oriole Publishing, 1991)