Complex sentence: Her design was begun before the war began because the Royal Navy anticipated being outnumbered by the combined German and Japanese battleships in the early 1940s and enough old guns and gun turrets were in storage to equip one battleship that could be built relatively quickly.
Split into simpler sentences: Her design was begun before the war began because the Royal Navy anticipated being outnumbered by the combined German and Japanese battleships in the early 1940s. Enough guns and gun turrets were in storage to equip one battleship that could be built relatively quickly.