Dornier Do-X Lufthansa SeaplaneDornier DO X seaplane airplane model. Perhaps the most dramatic flying boat ever built was the giant Dornier Do X. Conceived by Dr. Claudius Dornier, the Do X design took seven years to complete and two years to build. The giant flying boat was finally launched on July 12th, 1929. Financed by the German transport ministry, the plane was built on the Swiss portion of Altenrhein in order to avoid the Allied Commission. When complete, the Do X was the