The Siemens-Schuckert D.IV was a late-World War I fighter aircraft from Siemens-Schuckert (SSW). It reached service too late and was produced in too few numbers to have any effect on the war effort. Earlier designs Siemens-Schuckert's first production fighter aircraft was the Siemens-Schuckert D.I, which was based closely on the French Nieuport 17. Apart from the use of the Siemens-Halske Sh.I, a geared rotary engine in which the crankshaft and the propeller rotated in opposite directions, the D.I was in fact a fairly close copy of the Nieuport. By the time production D.Is appeared in 1917 however, the design was no longer competitive and after 95 had been built, production was cancelled, with the type serving mainly as an advanced trainer. Development work on the Siemens-Halske Sh.I culminated in the Siemens-Halske Sh.III, which developed . The new engine was fitted to a series of original prototype designs from the SSW works, the D.II, D.IIa and D.IIb. These featured a short, round section fuselage designed to fit a larger engine, leading to a rather stubby-looking aircraft which pilots later referred to as the flying beer barrel. Flight tests started in June 1917, and while the aircraft did not have a very high top speed, they showed outstanding rates of climb. The only serious concern was the extremely long landing gear needed to keep the huge 2-bladed prop clear of the ground. D.III Three more prototypes were ordered, one D.IIe, with the original sized wings, and two D.IIc's, fitted with shorter and longer span wings. After completion in October 1917, the design proved promising and in December an order for twenty long-span D.IIc's was placed with a smaller 4-bladed propeller that allowed for shorter landing gear legs. Deliveries of these aircraft, now known as D.III, began in January and were followed by an additional order for thirty in February. All fifty were delivered to front-line units in May, where they proved popular but after only 10 hours of service the engines started showing serious problems, overheating and seizing. Siemens blamed the problem on the Voltol-based oil that was used to replace scarce castor oil for lubricating the engine but the type was withdrawn from service and replaced by Fokker D.VIIs. When they were removed, Rudolf Berthold, commander of JG.II, noted that he wished "the Siemens fighter be made available again for front-line use as quickly as possible for, after elimination of the