During the interwar period, German pilots were trained secretly in violation of the treaty at Lipetsk Air Base in the Soviet Union. With the rise of the Nazi Party and the repudiation of the Versailles Treaty, the Luftwaffe's existence was publicly acknowledged on 26 February 1935, just over two weeks before open defiance of the Versailles Treaty through German re-armament and conscription would be announced on 16 March.[9] The Condor Legion, a Luftwaffe detachment sent to aid Nationalist forces in the Spanish Civil War, provided the force with a valuable testing ground for new tactics and aircraft.