Sperrle began the war with 120 aircraft, and for the first four months the German aviators failed to make an impact. Sperrle lost 20 percent of his strength in the failed attempt to seize Madrid in 1936. The material support provided was inadequate and left him with just 26 Ju 52s and two Heinkel He 70 aircraft by the end of January 1937. Sperrle's personal leadership and the dedication of senior officers prevented a collapse in morale. The cause of this defeat was the appearance of Soviet-designed and built Polikarpov I-15 and Polikarpov I-16 fighter aircraft in the Spanish Republican Air Force which won air superiority. Bombing raids against Cartagena and Alicante, and the Soviet air base at Alcalá de Henares, failed. Sperrle personally led an attack against the Republican Navy at Cartagena, sinking two ships. The Republican fleet was forewarned, however, and the majority put to sea and escaped the bombing. Attacks against Madrid, in which 40 tons of bombs were dropped from 19 November 1936, also failed. The bombing and shelling inflicted 1,119 casualties between 14 and 23 November, including 244 dead—303 buildings were hit. The Legion's bomber group temporarily gave up daylight bombing after the failed Fascist offensive.