Here is an article from 1943, the year everything changed for the Axis. The article explains all that was involved with the stout-hearted raid on the Ploesti oil fields in Rumania. 177 American bombers were sent to do the job.
"From Ploesti, the Nazis extracted oil and oil products which maintained the entire German and Italian fleets, and third of the whole German air force in Russia. Around the Ploesti installations, the Germans had raised a forest of antiaircraft guns of large and small calibers. They had built blast walls around plants' vital parts and spotted airdromes from which fighters could rise to intercept our bombers."