Junkers T.21
The Junkers J 21 (manufacturer's sales designations T 21 and H 21) was a reconnaissance aircraft designed in Germany in the early 1920s and produced in the Soviet Union at the Junkers plant at Fili for use by the Soviet Air Force. Design and development. The J 21 was an all-metal, parasol-wing monoplane of conventional configuration and fixed, tailskid undercarriage. The pilot and observer sat in tandem, open cockpits. Two prototypes were constructed at the Junkers factory in Dessau, the second with a wing of reduced area. Despite the fact that the prototypes were unable  to attain the performance that had been specified by the Soviets, series production commenced at Fili in August 1923 where it was known as the Ju 21 (Юнкерс Ю 21 in Cyrillic). The production version differed from the prototypes in having a BMW IV engine in place of the BMW III originally fitted, and carried machine gun armament for both the pilot and observer. Sluggish performance led to a few examples being fitted with L2 and L5 engines, but these provided little improvement. With performance only marginally better than the World War I-vintage de Havilland DH-9A that it had  been purchased to replace, the Ju 21 was itself soon replaced by newly built DH-9As built under license as the Polikarpov R-1. The type was also evaluated by the "Reichswehr"s clandestine training school at Lipetsk, but it was rejected due to its poor performance and the Heinkel HD 17 purchased instead.