Complex sentence: The Merlin engines were replaced with the larger, more powerful and slower-revving Rolls-Royce Griffons with 13 ft (4 m)-diameter contra-rotating propellers, the engine's distinctive noise often caused pilots to develop high-tone deafness.
Split into simpler sentences: The Merlin engines were replaced with the larger, more powerful and slower-revving Rolls-Royce Griffons with 13 ft (4 m)-diameter contra-rotating propellers. This engine's distinctive noise often caused pilots to develop high-tone deafness.