From March to September 1937, Lützow, now an "Oberleutnant" (first lieutenant), claimed five victories, including the first ever recorded claim by a Messerschmitt Bf 109 pilot. Flying a Bf 109 B, he shot down a Polikarpov I-15, a Soviet built biplane fighter aircraft, on 6 April 1937. On 26 April 1937, air elements of the Condor Legion targeted and bombed Guernica, an attack which has been characterised as a war crime by Wette and Ueberschär, but Lützow did not participate in the attack as he was on home leave from 8–29 April 1937. After he returned, Lützow claimed three more I-15s shot down, one on 22 May, another on 28 May, and his last on 18 August 1937. His final aerial victory in Spain was over a Polikarpov I-16, a monoplane fighter aircraft, which he shot down on 22 August 1937.