Complex sentence: They were used as ferry pilots and did not fly in combat, their primary job being to transfer new and repaired aircraft from rear areas to air bases and forward air fields, and to fly patched-up damaged aircraft back for more thorough repairs.
Split into simpler sentences: They were used as ferry pilots and did not fly in combat. Their job was to transfer new and repaired aircraft from rear areas to airbases and forward air fields and fly patched-up damaged aircraft back for more thorough repairs.