test bed use only, the Mo3 was a four-cylinder, (eight piston), opposed-piston engine designed to run horizontally. Tested from 1913, the problems found in testing the Mo3 were progressively solved after World War I with the Fo3 and later opposed piston diesels. Fo3From 1924, Junkers experimented with the Fo3, A vertical 5-cyl. opposed-piston diesel, which ran on a test bed in the summer of 1926, developing at 1,200 rpm. Mostly successful, the Fo3 did highlight the need for accurate dynamic balancing of the rotating components. Fo4 (a.k.a. SL1) The Fo4, benefiting from the experience gained with the Fo3, was a six-cylinder opposed-piston diesel engine, tested from 1928 and flown in the nose of a Junkers G.24 from 30 August 1929. Jumo 4 After the successful bench runs and flight tests, the Fo4 was refined into the certificated Jumo 4, enjoying limited success powering re-engined Junkers F24kay airliners of Deutsche Luft Hansa, remaining in service until 1939. Jumo 204Later production of refined Jumo 4s: Jumo 204A, 204B, and 204C, differing in airscrew drive arrangements. Napier CulverinThe Jumo 204 and 205 were licensed to Napier, who built a small number of Jumo 204 developments as the Napier Culverin just prior to the war. After the war, they mounted three Culverins in a triangle layout to produce the Napier Deltic, which was for some time one of the most powerful and compact diesel engines in the world. Work on this engine started in 1947 and engines were running by 1950. Applications Junkers F.24kay Junkers Ju 52/1mdo D-1974 (D-UZYP from 1937) Junkers Ju 86 Junkers G.38 and Japanese licensed Mitsubishi Ki-20 Blohm & Voss BV 138 Specifications (Jumo 204A) See also List of aircraft engines References Further reading * External links Multi-crankshaft opposed piston engines (french) Description and cutaway view (Jumo 205) OpposedPiston Engines.com's Jumo 204 Page Two-stroke diesel engines Aircraft diesel engines Opposed piston engines Junkers aircraft engines 1920s aircraft piston engines