1(military) A type of cruiser (the warship) common in the late 19th and early 20th centuries, carrying a small number of moderately-heavy main guns plus a large secondary battery of smaller guns and with armor protecting the sides and upper and lower decks, but lighter and with thinner armor and less powerful guns than a battleship; a mainstay of battle fleets around the turn of the 20th century, but displaced from this role by the more powerful battlecruiser after ca. 1908, becoming obsolescent by the time of WWI.