Complex sentence: Filming also took place aboard HMS "Victory" for scenes in episode two, as well as additional aerial shots of HMS "Invincible" and HMS "Gloucester" for the war games scenes in episode four.
Split into simpler sentences: Filming also took place aboard HMS "Victory" for scenes in episode two. Additional aerial shots of HMS "Invincible" and HMS "Gloucester" were taken for the war games scenes in episode four.