Emerald - class cruiser The " Emerald " class or E class was a class of two light cruiser s built for the Royal Navy . Following the " Cavendish " class , three ships of a new class were ordered in March 1918 , towards the end of World War I , designed to emphasise high speed at the cost of other qualities , for use against rumoured new high speed German cruisers - like the " Brummer " class - and particularly minelayers , in the North Sea . However , the third ship was cancelled in November 1918 . Design . The E class were based on the preceding " Danae " class , but had a very high ratio of length to beam , and only one more gun despite being much bigger and more expensive . Much was sacrificed to achieve , the horsepower was doubled and the hull increased by in length , and a 50 % increase in displacement . Only two ships were actually built , and completed in 1926 . Four propellers were necessary for the increased power , and were driven from two engine rooms . There were four boiler rooms , nos . 2 and 3 being arranged side - by - side with the exhausts trunked into a common funnel . The magazines were between boiler rooms nos . 2 and 3 and the forward engine room , and between boiler room no . 4 and the after engine room . This led to a bizarre funnel arrangement , accentuated further when in 1935 a longer catapult required the mainmast to be stepped forward of the after funnel , and the funnels were heightened by . In the early 1930s " Enterprise " was fitted with a prototype twin 6 " turret in place of her two forward single mounts ; and with trials of the turret proving successful it was retained on " Enterprise " for the rest of her career . The turret design was later installed in the " Leander " , " Amphion " and " Arethusa " classes . The turret installation occupied less space than the superimposed ' A ' and ' B ' guns of " Emerald " , therefore the bridge was placed further forward . The bridge was of a new design , being a single block topped by a director tower , rather than the traditional platforms built around the foremast and wheelhouse topped with a spotting top . This design of bridge would appear in the s . Nothwithstanding their age and outlandish appearance these two ships were still the fastest cruisers in the Royal Navy at the outbreak of World War II , " Emerald " exceeding in a full - power trial at full load in 1939 . Like the " Cavendish " class , they were mainly employed on the ocean trade routes , also seeing fleet service in the Far East . Modifications . In the mid - 1930s both ships were fitted with a catapult which replaced the out - moded flying - off platform and had HACS Mk . I added for the 4 in guns , which was fitted amidships between the searchlight platform and the after funnel . The funnels were raised at this time . Later proposals to increase the AA outfit by the addition of twin 4 in and multiple 2 pdrs were thwarted by the outbreak of war . " Emerald " had received two quadruple . 5 machine guns before the war , then during refit between August 1942 and April 1943 she landed the after 6 in , two 2 pdr singles and the . 5 machine guns to receive instead six power - operated twin 20 mm , two quadruple 2 pdr and radars Type 273 ( centimetric target indication ) , 281 ( air warning ) , 282 ( pom - pom ranging ) and 285 ( HACS ranging ) . In April 1944 six 20 mm singles were added and the catapult was removed . " Enterprise " landed two 6 in singles in 1941 and had one quadruple 2 pdr fitted . She later had four single 20 mm fitted and then , in the course of a long refit between the end of December 1942 and October 1943 , she lost the single 2 pdr and 20 mm weapons , receiving six twin power - operated mountings in lieu . The two 6 in were reinstated and a second quadruple 2 pdr fitted . She was fitted with radars Type 272 ( centimetric target indication ) , 281 , 282 , 284 ( 6 inch gun ranging ) , and 285 . In February she had an additional four single 20 mm fitted and the catapult was removed .