The Lipetsk fighter-pilot school (), also known as WIWUPAL from its German codename Wissenschaftliche Versuchs- und Personalausbildungsstation "Scientific Experimental and Personnel Training Station", was a secret training school for fighter pilots operated by the German Reichswehr at Lipetsk, Soviet Union, because Germany was prohibited by the Treaty of Versailles from operating an air force and sought alternative means to continue training and development for the future Luftwaffe. It is now the site of Lipetsk Air Base. Background The Treaty of Versailles, signed on 28 June 1919, prohibited Germany from operating any form of air force after the country had lost the First World War. Initially, it also prohibited the production and import of any form of aircraft to the country. In 1922, the clause on civilian aircraft was dropped and Germany was able to produce planes again, followed in 1923 with the country regaining control of its airspace. The operation or production of aircraft for military means was however still prohibited. The German military, the Reichswehr, was well aware of the value of air warfare and was determined not to fall too far behind in knowledge and training. For this purpose alternative means, outside Germany, were explored. Germany had normalised its relations with the Soviet Union in 1922, with the signing of the Treaty of Rapallo. At the time, both countries were outcasts in the world community. Initially, Germany was unwilling to break the Treaty of Versailles. This attitude changed however in 1923, when French and Belgian troops occupied the Ruhr area after Germany defaulted on reparations payments. In light of the events of the Ruhrkampf, the German Army ordered 100 new aircraft from Fokker in the Netherlands, among them 50 newly developed Fokker D.XIIIs. Additionally, the German Navy had also ordered a small number of planes. With the end of the Ruhrkampf in September, Germany was at a loss as to how to utilize the planes which were due for delivery in 1924. The Soviet Union was approached and showed an interest in allowing Germany to develop aircraft in the country; the German manufacturer Junkers had already been operating a production facility for military aircraft near Moscow since 1923. In June 1924, retired Colonel Hermann von der Lieth-Thomsen became a permanent representative of the Reichswehr's Truppenamt, the secret General Staff of the German Army, in Moscow. At the same time, seven German instructors were sent to the Red Air