[7] This time of superiority was short lived, with the arrival of large numbers of more modern aircraft from the Soviet Union, including the Polikarpov I-15 biplane and the new Polikarpov I-16 monoplane,[8] together with the Tupolev SB bomber, which was 110 km/h (68 mph) faster.

[9] The He 51 was soon withdrawn from fighter duty and relegated to the ground-attack role by both the Legion Condor and the Nationalists.

[9][11] It was replaced in the fighter role by the Fiat CR.32 in the Fascist Nationalist Air Force, with the Legion Condor receiving Messerschmitt Bf 109s from April 1937.

After the war, the 46 surviving aircraft would be joined by another 15 newly built airframes, and remain in service in Spain until 1952.

[citation needed] The He 51 lasted in front-line service with the Luftwaffe until 1938, when it was relegated to use as an advanced trainer duties with the Jagdfliegerschulen[14] for the first few years of World War II.