HMS Warrior illustrates how the frigate grew into an armoured ship comparable to the battleships of its day. Such ships were too costly and important to deploy everywhere, so the cruiser emerged as a reduced frigate able to scout, protect or raid commerce, and show the flag. Its armament needed to deter lesser ships and threaten stronger ones without making it a capital ship. Torpedoes gave a cruiser a dangerous chance against a superior opponent even though battleship guns could engage it from farther away.
Chapter · 18:26-28:50
How the ironclad frigate created the cruiser
Once ironclad frigates became battle-fleet ships, navies needed a smaller and cheaper vessel to resume their traditional cruising work.