Created in November 1943, the Fifteenth Air Force was the direct descendant of the American Ninth and Twelfth Air Forces that had fought in the Mediterranean since the summer of 1942. Its force included 210 B-17 Flying Fortress and 90 B-24 Liberator bombers escorted by P-38 Lightning, P-47 Thunderbolt, and P-51 Mustang fighters. They took the air battle against the Axis to areas Allied bombers based in England could not reach: southern Germany, Austria, eastern Europe, and the Balkans. Their reach in the Balkans included the oil refineries at Ploesti, Romania, vital to Germany's war effort. Its crews fought the weather, as well as the enemy, by flying over the Alps to reach many of their targets and made a significant contribution to the victory over the Axis powers and Nazi Germany.