Complex sentence: Its main use was in the Westland Wyvern carrier-based heavy fighter, the turboprop engine replacing the Wyvern prototype's original Rolls-Royce Eagle piston engine in production aircraft.
Split into simpler sentences: Its main use was in the Westland Wyvern carrier-based heavy fighter. The prototypes had used the Rolls-Royce Eagle piston engine, but Pythons were used in production aircraft.