Complex sentence: In RAF circles it was known that the Lysander was no longer a front line aircraft, and had been relegated to towing targets for firing practice, or at best scanning the ocean in support of air/sea rescue and recovery of downed aircrews.
Split into simpler sentences: In RAF circles it was known that the Lysander was no longer a front line aircraft. It had been relegated to towing targets for firing practice or at best scanning the ocean in support of air/sea rescue and recovery of downed aircrews.