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The two-seater all-metal low-wing A 25 (development line: J 11 – A 20 – A 25) hardly differed externally from the multi-purpose aircraft A 20 from 1923. Essentially, it was the same aircraft that had been remotorized. In the meantime, the Junkers L 2 aircraft engine, which had proven itself in many ways in the use of the G 24 three-engine commercial aircraft, was available. From the period 1925 / 1926 it was installed in newly built A 20 series aircraft, which were then offered under the type designation A 25. In this way, the Daimler D III a and BMW III a engines, which had become obsolete and less powerful, were replaced. Understandably, the "Junkers Motorenbau GmbH" (JUMO) tried to sell self-developed and field-tested aircraft engines with Dessau aircraft. One way to achieve this was remotorisation.

As early as 1923, the Junkers plant in Fili/Moscow had delivered 20 A20 aircraft for Soviet air forces, assembled from components prefabricated in Dessau. Several of them were converted to A 25 in 1926 with the Junkers L 2 engine, but the Soviet model designation Ju 20 was retained. The Baltic Fleet, the Black Sea Fleet and the Polar Fleet became increasingly interested in the aircraft; it was used on floats or snow runners mainly for reconnaissance, liaison and courier flights.

These naval aircraft were used (also with later re-conversion to the Junkers L 5 aircraft engine) until 1930, in the polar fleet even until 1933. In the water- and snow-rich areas typical of operations, the aircraft's all-duralumin construction proved to be particularly useful because of its insensitivity to weather and moisture.