The 12-engine Dornier Do X, the largest, heaviest and most powerful flying boat in the world at that time, was designed as a transatlantic passenger aircraft. Although it was equipped with twelve radial engines, each of them boasting nine cylinders, its performance on the planned long-distance flights was not particularly convincing. The Do X achieved a cruise speed of 175 km/h at an altitude of 1,000 metres. However, the plane required 14 minutes to reach this speed and altitude. These limitations combined with the large number of required refueling stops meant this impressive aircraft was not commercially viable.