With the treaty of Versailles preventing any other form of pilot training in Germany, large numbers of gliding clubs and schools were formed there after World War I. Later, when planning the invasion of France, the German military was faced with the problem of the Belgian fort of Eben Emael which dominated the River Meuse. Someone (according to some reports, Adolf Hitler himself) pointed out that the top of the fort was a flat grassy expanse on which gliders could land.