Initially, civil aviation schools within Germany were used, yet only light trainers could be used in order to maintain the façade that the trainees were going to fly with civil airlines such as Deutsche Luft Hansa. To train its pilots on the latest combat aircraft, Germany solicited the help of the Soviet Union, which was also isolated in Europe. A secret training airfield was established at Lipetsk in 1924 and operated for approximately nine years using mostly Dutch and Soviet, but also some German, training aircraft before being closed in 1933.