Complex sentence: Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the "Merlin" following the company convention of naming its piston aero engines after birds of prey.
Split into simpler sentences: Rolls-Royce Limited designed and built the engine which was initially known as the PV-12. It known as the "Merlin" following the company convention of naming its piston aero engines after birds of prey.