The protected cruiser was a type of naval cruiser that was armored, but not so heavily as armored cruisers. Most of the 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.
A displacement of armored cruisers was about 2500 - 7000 tones. Their main armament were several - up to dozen single 4in - 5in (100mm - 152mm) guns. Their speed was usually 18 - 23 knots.
The protected cruisers appeared about 1880 and disappeared about 1910, when the Navies started to build light cruisers, with armored sides and decks instead.
need origin, usage in other navies
A few protected cruisers have been preserved 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).