 The Spanish Civil War experiences by the Condor Legion helped perfect tactics and techniques required in organising and coordinating operations with land forces.The experience permitted large numbers of airmen to gain the navigational skills necessary to carry out future strategic bombing operations.In June 1939, Jeschonnek penned a study in which he wrote, "[close air support] is the most difficult mission that could be given to the air force" and it required "the closest liaison between Luftwaffe commanders and the supported army units."