Complex sentence: WW2 saw much more of BUSM's precision engineering capacity switched to manufacturing arms than in WW1 including Naval gun sights and the technically very demanding precision cast wheelhouse for the Rolls-Royce Merlin aero engine.
Split into simpler sentences: WW2 saw much higher percentage of BUSM's precision engineering capacity switched to manufacturing arms than in WW1. Products included Naval gun sights and the technically very demanding precision cast wheelhouse for the Rolls-Royce Merlin aero engine.