Light cruiser A light cruiser is a type of small - or medium - sized warship . The term is a shortening of the phrase " light armored cruiser " , describing a small ship that carried armor in the same way as an armored cruiser : a protective belt and deck . Prior to this smaller cruisers had been of the protected cruiser model , possessing armored decks only . History . The first small steam powered cruisers were built for the British Royal Navy with HMS " Mercury " launched in 1878 . Such second and third class protected cruisers evolved , gradually becoming faster , better armed and better protected . Germany took a lead in small cruiser design in the 1890s , building a class of fast cruisers copied by other nations . Such vessels were powered by coal - fired boilers and reciprocating steam engines and relied in part on the arrangement of coal bunkers for their protection . The adoption of oil - fired water - tube boilers and steam turbine engines meant that older small cruisers rapidly became obsolete . Furthermore , new construction could not rely on the protection of coal bunkers and would therefore have to adopt some form of side armoring . The British " Bristol " group of cruisers ( 1909 ) were a departure from previous designs ; with turbine propulsion , mixed coal and oil firing and a 2 inch protective armoured belt as well as deck . Thus , by definition , they were armoured cruisers , despite displacing only 4 , 800 tons ; the light armored cruiser had arrived . The first true modern light cruisers were the ( 1911 ) which had all oil - firing and used lightweight destroyer - type machinery to make . World War I . By World War I , British light cruisers often had either two 6 inch ( 152 mm ) and perhaps eight 4 inch ( 100 mm ) guns , or a uniform armament of 6 inch ( 152 mm ) guns on a ship of around 5 , 000 tons , while German cruisers progressed during the war from 4 . 1 inch ( 105 mm ) to 5 . 9 inch ( 150 mm ) guns . Cruiser construction in Britain continued uninterrupted until Admiral " Jacky " Fisher ' s appointment as First Sea Lord in 1904 . Due in part to the desire to curtail excess expenditures in light of the increasing cost of keeping up with German naval production and in part because he felt the type to be outdated , Fisher authorized few new cruisers and scrapped 70 older ones . Fisher ' s belief that battlecruiser s would take the place of light cruisers to protect commercial shipping soon proved impractical , as their high construction cost precluded their availability in sufficient numbers to do so , and destroyers were too small for scouting duties . The group of 21 cruisers begun in 1910 proved excellent in scouting in all types of weather and could carry enough fuel and ammunition to guard the trade routes . The , launched three years later , was also successful . British designers continued enlarging and refining subsequent cruiser designs throughout the war . The Germans built a number of light cruisers in the belief that they were good multi - purpose vessels . They were bigger , slower and less maneuverable than their British counterparts but , through a successive series of classes , improved consistently in seagoing qualities . However , the Germans were very late in adapting guns for them ( not until the of 1913 ) ; Grand Admiral Alfred von Tirpitz ' s recalcitrance over the issue overrode the desires of others in the German Navy . They completed the last two of their cruisers in 1906 and 1907 and followed them up with four s and two s between 1905 and 1908 . These last two classes , larger and faster than the " Bremens " , were armed the same ( 10 guns ) and carried less deck armor . Other major powers concentrated on battleship construction and built few cruisers . Between the wars . The United States resumed building light cruisers in 1918 , largely because the ships it then had in service had become obsolete . The first of these , the 10 ships , displaced 7050 tons and were armed with 12 guns . Eight of these guns were mounted in double - story casemate s at the bow and stern , a reflection of the US prewar preference for heavy end - on fire . Fast and maneuverable , they were well - liked as seaboats despite being very wet in rough weather . The term light cruiser was given a definition by the London Naval Treaty of 1930 . Light cruisers were defined as cruisers having guns of 6 . 1 inch ( 155 mm ) or smaller , with heavy cruiser s defined as cruisers having guns of up to 8 inch ( 203 mm ) . In both cases , the ships could not be greater than 10 , 000 tons . After 1930 , most naval powers concentrated on building light cruisers since they had already built up to the maximum limitations allowed under the Washington treaty . Japan laid down its four s between 1931 and 1934 . The political climate from 1936 to 1939 gave the renewed building of light cruisers an added urgency . The British built 11 during this period , which culminated in the two ships , armed with 12 guns . The new ships were larger and better armored than other British treaty cruisers , with a belt in the Towns and were capable of 32 . 5 knots , but for the most part tried to stay within past treaty limitations . The US also attempted to follow treaty limitations as it completed seven of its nine s between 1938 and September 1939 . These ships were an answer to Japan ' s " Mogami " s and were an indication of rising tensions in the Pacific theater . Japan , now considering itself under no restrictions , began rearming its " Mogami " s with 10 guns . World War II . In the World War II era , light cruisers had guns ranging from 5 inch ( 127 mm ) , as seen in the US and British anti - aircraft cruisers , to 6 . 1 inch , though the most common size by far was 6 inch . The " Atlanta " s and " Dido " s were borne out of the tactical need for vessels to protect aircraft carriers , battleships and convoys from air attack . Heavy cruisers usually had a battery of 8 inch ( 203 mm ) guns . In the years leading up to World War II , with the London Naval Treaty making it impossible to build a balanced heavy cruiser design within tonnage limits , this led to the construction of a great number of light cruisers of 10 , 000 ton with twelve to fifteen guns that were otherwise identical to heavy cruisers . Heavy cruiser construction was phased out in Britain , France and Italy during the mid - 1930s . However , the breakout of World War II allowed nations to skirt the London Treaty and exceed the 10 , 000 ton limit . By the end of the war , the US Navy ' s ships classed as " large cruisers " had displacements of nearly 30 , 000 tons ( the ) , while light cruisers stayed in the region of 10 , 000 tons ( although sometimes reaching 12 , 000 or 13 , 000 tons ) . Most modern guided missile cruisers have a similar displacement ( 10 , 000 tons for , 12 , 000 for , 28 , 000 for ) . Light cruisers today . of the Peruvian Navy is the only light cruiser still in active service . Another four are preserved as museum ships : in London , in Belfast , in Buffalo , New York , and " Mikhail Kutuzov " at Novorossiysk . Similar ships include the protected cruisers ( St . Petersburg ) and ( Philadelphia , Pennsylvania ) , and the bow of the " Puglia " ( Italy ) . United States Navy classification . In the United States Navy , light cruisers have the hull classification symbol CL . Both heavy cruiser s and light cruisers were classified under a common CL / CA sequence after 1931 , hence there are some missing hull numbers , see List of United States Navy cruisers . After the development of seaborne guided missiles in the 1950s , all remaining cruisers armed solely with guns , regardless of caliber were redesignated as " Gun Cruisers " ( hull classification symbol CA ) , with guided missile cruisers ( which generally carry some gun armament ) gaining the new hull classification symbol CG . By the 1975 fleet realignment , all gun cruisers were out of the fleet .