Dornier Do D bis in Yugoslav service
Developed as a floatplane torpedo-bomber version of the Dornier Do B and Do C, Merkur/Komet III, for Japan the Do D instead found succesful sales in Yugoslavia.
The initial Do D prototype was a minimal modification to the Do C, with a robust independant suspension to the floats to allow the carriage of a torpedo against the belly. Thw aircraft was somehow approved by the Interallied Aviation Guarantee Committee as a "civilian aircraft", and first flew in October 1924. The aircraft performed successfully in Japan, but no order was forthcoming.
Back in Germany the design was updated with the ongoing modifications to the Do B including an enlarged and revised tailplane design as the Do D bis, and in 1926 Yugoslavia ordered 10, and 9 were delivered in 1927. The 10th aircraft was written off in an accident on Lake Constance before delivery, and instead a new aircraft was built with a revised configuration. The rear gunners position was deleted, and instead the cockpit positioned behind the wing, while the cabin was moved forward. In service this arrangement provided poor pilot visibility and was not continued, while the aircraft was modified back to standard configuration after rebuild from an accident in Yugoslav service.
A second batch of 14 aircraft was ordered and delivered in 1929. The most significant change was that these aircraft lacked the recessed belly for carriage of a torpedo, as that was now not a mission for the aircr.aft. Strangely Yugoslavia had no aerial torpedos, and evidently no access to them. Test with French shipborne torpedos revealled that the aircraft was so underpowered for the payload that they battled to climb to a mere 60m, and that air launching marine torpedos was completely ineffective.
two aircraft of the second batch were also fitted with modified "trousers" attaching the floats. The large airfoil section struts made the aircraft sluggish in the turn, and so a reduced size fitting was trialed. While the truning abilities of the aircraft were enhanced, the aerodynamic interference between the sections negated any advantage.
In 1939 12 aircraft were still in service, when they were phased out and replaced by the Dornier Do 22J and decommisioned. But some aircraft were not scrapped and were used as squadron hacks, with 3 aircraft being captured by the Italians after the invasion.