In August 1936, these planes flew operationally for the first time in the Spanish Civil War. The results of the first combat engagements were a little disturbing. The He 51 came off second best not only in comparison with the latest Soviet I-16, but even with machines of a similar design such as the I-15 or I-153. Despite all the favor for Heinkel's work shown by head of the Luftwaffe Hermann Gring, even he could not influence the fate of the He 51. Chief Inspector of the Luftwaffe Ernst Udet, hero of the First World War and a pilot of consummate skill himself, conducted several mock battles with the plane against the Arado Ar 68, piloted by the best pilots of the Luftwaffe. The He 51 lost repeatedly and its fate was sealed. Most of the machines constructed were transferred to training and other units. At the beginning of World War II the role of this machine was minimal.