Werner Mölders
Oesau started his operational career with the Condor Legion, along with future contemporary aces such as Werner Mölders and Adolf Galland. He was one of the first to join 3. "Jagdgruppe" 88 in Spain in April 1938. The "Staffel", commanded by Werner Mölders, took part in the Spanish Civil War where Oesau claimed nine victories, flying 130 combat missions. For this he received the Spanish Cross ("Spanienkreuz") in Gold with Diamonds. He was also wounded in this conflict which earned him the Spanish Wound Badge.