Complex sentence: The Admiralty had already tried Fighter Catapult Ships, converted freighters equipped with a single rocket-launched fighter, manned by Naval crews, and they ordered 50 more rocket-propelled catapults for fitting aboard merchant ships.
Split into simpler sentences: The Admiralty had already tried Fighter Catapult Ships-converted freighters equipped with a single rocket-launched fighter, manned by Naval crews. They ordered 50 more rocket-propelled catapults for fitting aboard merchant ships.