protected cruiser

(military, nautical) A type of cruiser (the warship) carrying moderately-heavy main guns (although considerably lighter than those of a battleship) in armored turrets or other enclosures and having the machinery and magazine spaces protected by an armored lower deck, but leaving the sides of the ship unarmored (relying on the ship's coal bunkers to absorb hits to the sides of the hull) to save weight and allow for a high speed and long range; common in the late 19th century, but rendered obsolescent by the armored cruiser around 1900 as technological advances reduced the weight penalty of a side-mounted armor belt and made warships lacking belt armor increasingly vulnerable to enemy gunfire.