the eleven-cylindered Siemens-Halske Sh.III, with less drag and less net torque. Used on several late war types, notably the Siemens-Schuckert D.IV fighter, the new engine's low running speed, coupled with large, coarse pitched propellers that sometimes had four blades (as the SSW D.IV used), gave types powered by it outstanding rates of climb, with some examples of the late production Sh.IIIa powerplant even said to be delivering as much as 240 hp. One new rotary powered aircraft, Fokker's own D.VIII, was designed at least in part to provide some use for the Oberursel factory's backlog of otherwise redundant Ur.II engines, themselves clones of the Le Rhône 9J rotary. Because of the Allied blockade of shipping, the Germans were increasingly unable to obtain the castor oil necessary to properly lubricate their rotary engines. Substitutes were never entirely satisfactory - causing increased running temperatures and reduced engine life. Postwar By the time the war ended, the rotary engine had become obsolete, and it disappeared from use quite quickly. The British Royal Air Force probably used rotary engines for longer than most other operators. The RAF's standard post-war fighter, the Sopwith Snipe, used the Bentley BR2 rotary as the most powerful (at some ) rotary engine ever built by the Allies of World War I. The standard RAF training aircraft of the early post-war years, the 1914-origin Avro 504K, had a universal mounting to allow the use of several different types of low powered rotary, of which there was a large surplus supply. Similarly, the Swedish FVM Ö1 Tummelisa advanced training aircraft, fitted with a Le-Rhone-Thulin rotary engine, served until the mid thirties. Designers had to balance the cheapness of war-surplus engines against their poor fuel efficiency and the operating expense of their total-loss lubrication system, and by the mid-1920s, rotaries had been more or less completely displaced even in British service, largely by the new generation of air-cooled "stationary" radials such as the Armstrong Siddeley Jaguar and Bristol Jupiter. Experiments with the concept of the rotary engine continued. The first version of the 1921 Michel engine, an unusual opposed-piston cam engine, used the principle of a rotary engine, in that its "cylinder block" rotated. This was soon replaced by a version with the same cylinders and cam, but with stationary cylinders and the cam track rotating in lieu of a crankshaft. A later version abandoned the cam altogether and used three coupled