Forsyth, Robert: Aces of the Legion Condor

For Germany, the Spanish Civil War proved a perfect testing ground for new technologies and tactics. During the war, some 19,000 German 'volunteers' formed an aviation group called the Legion Condor in support of the fascists. Originally flying He-51s, they were soon upgraded to 109s. These fighters proved dominant in the Spanish skies, and many members of the legion scored five or more kills during the fighting.