Protected cruiser armour scheme — a cross-section (armour in red)
Protected cruisers were a type of naval cruiser of the late 19th century. They were so known because they had only a minimal amount of armor compared to existing "armored" cruisers. In around 1910, when armor plate began to increase in quality and engines became lighter, they were superseded by light and heavy cruisers.
Most of their armor was used on the special deck inside the vessel, protecting boilers and steam machines, trapezoid-like in cross-section. Also guns and conning tower could be armored.
The armor tended to range from 2 to 3 inches (5 to 7.5 cm) in thickness.
The displacement of protected cruisers was about 2500 - 7000 tons. Main armament was up to a dozen single guns between 3.9 and 6 inches (100mm - 152mm). Speed was usually about 18 - 23 knots.
Protected cruisers appeared about 1880 and disappeared about 1910, when countries started to build light cruisers, with armored sides and decks instead.
need origin, usage in other navies
A few protected cruisers are in existence as museum ships:
The first protected cruiser of the "New Navy " was the USS Atlanta, launched in October 1884, soon followed by the Boston in December, and Chicago a year later. A numbered series of cruisers began with Newark (Cruiser No. 1), although Charleston (Cruiser No. 2) was the first to be launched, in July 1888, and ending with another Charleston, Cruiser No. 22, launched in 1904.
The reclassification of 17 July 1920 put an end to the US usage of the term "protected cruiser", the existing ships designated as plain "cruisers" with new numbers (so that the armored cruisers could retain their numbers unchanged).