Dornier Do Y (Dornier Do 15)
The Dornier Do Y was Dornier's second design for a future bomber for the nascent Luftwaffe.
Following from the 4-engined Do P, the Do Y was a 3-engined design officially described as a "transport" to avoid the restrictions of the Treaty of Versailles, first flying in October 1931.
Yugoslavia was needing to upgrade their bomber fleet, and purchased 4 aircraft form Dornier for testing alongside examples of Junkers G.24 and Avia Fokker F.39. In mid-1931 the US granted a moratorium on War Debt repayments left Dornier not being paid for the construction of the aircraft from either the German government or Yugoslavia. In response Dornier embarked the first 2 aircraft on an eastern European marketing tour which resulted in no sales, but by the end of 1932 the sale to Yugoslavia was renegotiated and they were delivered to the Royal Yugoslav Air Force.
The remaining 3rd and 4th aircraft were flown to the Dornier plant in Switzerland and given Swiss registrations. While there they were significantly upgraded, including with new more powerful engines, and were delivered to Yugoslavia in 1937. These aircraft were redesignated as Do 15 by Dornier in Germany, but Yugoslavia continued referring to them using the original Do Y.
In Yugoslavia the aircraft shed their "transport" guise and were finally fitted with armaments.
Since the aircraft quickly became obsolete as bombers, they were used for reconnaissance, transport and communications, being further modified for paratrooping at the start of the War.
All four aircraft survived the Axis invasion, with 1 being transferred to the Air Force of the Independent State of Croatia.