A light cruiser is a warship that is not so large and powerful as a regular (or heavy) cruiser, but still larger than ships like destroyers. They were first built in Britain with Mercury in 1879, and gradually became faster and more powerful, with greater numbers of uniform size main guns. Germany took the lead in light cruisers in the 1890s, building a class of fast cruisers copied by other nations.
By World War I, British light cruisers often had either two 6 inch (200 mm) and perhaps eight 4 inch (100 mm) guns, or a uniform armament of 6 inch (200 mm) guns, while German cruisers progressed during the war from 4.1 inch (100 mm) to 5.9 inch (150 mm) guns.
In the Washington Naval Arms Limitation Treaty of 1920, light cruisers were defined as cruisers having guns of 6.1 inch (150 mm) or smaller, with heavy cruisers defined as cruisers having guns of up to 8 inch (200 mm).
In the World War II era, light cruisers had guns ranging from 5.00 inch (127 mm) to 6.1 inch (150 mm), the most common size being 6in (152mm), while heavy cruisers usually had a battery of 8 inch (200 mm) guns. This was a significant difference in destructive power, since 8 inch (200 mm) shells were over twice the weight of 6 inch (200 mm) shells. Light cruisers were nevertheless useful for fire-support and as fleet escorts, and heavily used.
Four light cruisers are still in existence: HMS Belfast (1938) in London, HMS Caroline in Belfast External site (scroll down) (http://www.battleships-cruisers.co.uk/caroline_class.htm) External site (http://www.royal-navy.mod.uk/static/pages/2474.html) Little Rock (Buffalo), and Colbert (Bordeaux). Similar ships include the protected cruisers Aurora (St Petersburg), part of Puglia (Italy) and Olympia.
In the United States Navy, light cruisers have the hull classification symbol CL. Both heavy cruisers and light cruisers were classified under CL after 1931, hence there are some missing hull numbers.