The key to the battle was Nationalist air superiority, provided by the Italian "Aviazione Legionaria" and German "Condor Legion" squadrons that flew under the "Aviación Nacional" markings. Some 500 first class planes were available on the Nationalist side (Savoia 79, Savoia SM-81, Breda 20, Heinkel 111, Dornier 17, Junker 52 and 6 Ju 87 bombers, and Bf 109 and CR-42 fighters) against only some 35 modern fighters and some 40 second class aircraft of the Spanish Republican Air Force. In July, the Legion Condor had destroyed 76 Republican planes and by August the Republican Air Force had lost air superiority in the area. The Republican planes were outnumbered by at least two to one, and most of the experienced Soviet pilots had been withdrawn. Republican anti-aircraft defenses proved to be inadequate and many planes were destroyed on ground. The Nationalists used their bombers to cut the pontoon bridges on the Ebro, and as a flying artillery to smash the Republican positions in the sierras, and to destroy their supply lines: "Republican communications were bombed to oblivion and, as so many international brigader memoirs testify, their troops were blasted off the bare and rocky hillsides by the sheer force of the incendiary materiel launched."