Complex sentence: HMS "Lightning" was a torpedo boat, built by John Thornycroft for the Royal Navy, which entered service in 1876 and was the first seagoing vessel to be armed with self-propelled Whitehead torpedoes.
Split into simpler sentences: HMS "Lightning" was a torpedo boat, built by John Thornycroft for the Royal Navy. She was the first seagoing vessel to be armed with self-propelled Whitehead torpedoes.