Duks in Royal Serbian Air Force

In mid-1909, The Duks factory made their first aircraft, the Duks airship "Jastreb." The test flights were not performed because the factory couldn't provide the appropriate engine. The aircraft was nevertheless shown at an aviation exhibit at the end of 1909, together with the aircraft of famous manufacturers from Europe.

In the summer of 1910, the Duks factory made the first aircraft modeled on the Farman HF III. It was named Duks I. It was different from the original construction by the type and the engine power, redesigned tail and reduced angle of the wing setting. The ENW 60HP (46kW) engine was more powerful, but also twice the weight of the original. It turned out that these changes didn't bring the improvement of flight performance, and there was also a problem with the center of gravity. These flaws were fixed during the test flights and the aircraft was delivered to its buyer. The factory soon made another aircraft Duks II, which was significantly lighter.

Unfortunately, the Duks biplane was not accepted as a military aircraft by the Ministry of the Army. It was placed in the factory hangar, and it would be delivered to the Kingdom of Serbia the following year.