The Treaty of Versailles and its consequences to any meaningful German aviation production demanded drastic measures. In Junkers’ case was the settling of a factory at the Fili western suburb of Moscow. The J21 (Russian designation) was design conceived in 1922-23 by Ernst Zindel as a recon parasol monoplane for the Soviets. Being a Junkers, it was built in Duraluminium, corrugated, of course. The Dessau-built prototype made its maiden flight in June 1923. The development in Germany included a considerable reduction of wing area for structural reasons among other things. Transported to Fili, the two German prototypes opened the road to series production there. That production amounted to around 120 units, the last one delivered on 1926. However, the Soviet forces found their J21s lacking: the only 240hp of the BMW IVa engine left them underpowered. On account of that some of them ended in the less demanding civil airline sector. Junkers tried some of their more powerful engines (L2 and L5) through to no avail.
One of the more curious feature of the J21 was the two jettisonable fuel tanks at either side of the fuselage. Pretty neat it was, methinks.